Patent Application
20090133158
Plants are hosts to thousands of infectious diseases caused by a vast array of phytopathogenic fungi, bacteria, viruses, oomycetes and nematodes. Plants recognize and resist many invading phytopathogens by inducing a rapid defense response. Recognition is often due to the interaction between a dominant or semi-dominant resistance (R) gene product in the plant and a corresponding dominant avirulence (Avr) gene product expressed by the invading phytopathogen. R-gene triggered resistance often results in a programmed cell-death, that has been termed the hypersensitive response (HR). The HR is believed to constrain spread of the pathogen.
How R gene products mediate perception of the corresponding Avr proteins is mostly unclear. It has been proposed that phytopathogen Avr products function as ligands, and that plant R products function as receptors. In this receptor-ligand model binding of the Avr product to a corresponding R product in the plant initiates the chain of events within the plant that produces HR leads to disease resistance. In an alternate model the R protein perceives the action rather than the structure of the Avr protein. In this model the Avr protein is believed to modify a plant target protein (pathogenicity target) in order to promote pathogen virulence. The modification of the pathogenicity protein is detected by the matching R protein and triggers a defense response. Experimental evidence suggests that some R proteins act as Avr receptors while others detect the activity of the Avr protein.
The production of transgenic plants carrying a heterologous gene sequence is now routinely practiced by plant molecular biologists. Methods for incorporating an isolated gene sequence into an expression cassette, producing plant transformation vectors, and transforming many types of plants are well known. Examples of the production of transgenic plants having modified characteristics as a result of the introduction of a heterologous transgene include: U.S. Pat. Nos. 5,719,046 to Guerineau (production of herbicide resistant plants by introduction of bacterial dihydropteroate synthase gene); 5,231,020 to Jorgensen (modification of flavenoids in plants); 5,583,021 to Dougherty (production of virus resistant plants); and 5,767,372 to De Greve and 5,500,365 to Fischoff (production of insect resistant plants by introducing Bacillus thuringiensis genes).
In conjunction with such techniques, the isolation of plant R genes has similarly permitted the production of plants having enhanced resistance to certain pathogens. Since the cloning of the first R gene, Pto from tomato, which confers resistance to Pseudomonas syringae pv. tomato (Martin et al. (1993) Science 262: 1432-1436), a number of other R genes have been reported (Hammond-Kosack & Jones (1997) Ann. Rev. Plant Physiol. Plant Mol. Biol. 48:575-607). A number of these genes have been used to introduce the encoded resistance characteristic into plant lines that were previously susceptible to the corresponding pathogen. For example, U.S. Pat. No. 5,571,706 describes the introduction of the Ngene into tobacco lines that are susceptible to Tobacco Mosaic Virus (TMV) in order to produce TMV-resistant tobacco plants. WO 95/28423 describes the creation of transgenic plants carrying the Rps2 gene from Arabidopsis thaliana, as a means of creating resistance to bacterial pathogens including Pseudomonas syringae, and WO 98/02545 describes the introduction of the Prf gene into plants to obtain broad-spectrum pathogen resistance.
Bacterial spot disease of tomato and pepper, caused by the phytopathogenic bacterium Xanthomonas campestris pv. vesicatoria (Xcv), can be devastating to commercial production of these crops in areas of the world with high humidity and heavy rainfall. While control of Xcv in commercial agriculture is based largely on the application of pesticides, genetic resistance to bacterial spot disease has been described in both tomato and pepper (Cook and Stall (1963) Phytopathology 53: 1060-1062; Cook and Guevara (1984) Plant Dis. 68: 329-330; Kim and Hartman (1985) Plant Dis. 69: 233-235; Jones and Scott (1986) Plant Dis. 70: 337-339). Of the two hosts, genetic resistance in pepper has been better characterized. Several single loci (Bs), Bs2, and Bs3) that confer resistance in a “gene-for-gene” manner have been identified (Hibberd et al. (1987) Phytopathology 77: 1304-1307). Moreover, the corresponding avirulence genes (avrBs1, avrBs2, and avrBs3) have been cloned from Xcv (Swanson et al. (1988) Mol Plant-Microbe Interact. 1:5-9; Minsavage et al. (1990) Mol. Plant-Microbe Interact. 3: 41-47). Genetic and molecular characterization of these avirulence genes has provided a great deal of information concerning the interaction between Xcv and pepper (Kearney et al. (1988) Nature 332: 541-543; Kearney and Staskawicz (1990) Nature 346: 385-386; Herbers et al. (1992) Nature 356: 172-174; Van der Ackerveken et al. (1992) Plant J. 2: 359-366). More recently, the Bs3 gene of pepper has been isolated and sequenced (U.S. Pat. No. 6,262,343)
Xcv employs a type III secretion (T3S) system to inject an arsenal of about 20 effector proteins into the host cytoplasm that collectively promote virulence (Thieme et al. (2005) J. Bacteriol. 187:7254). R protein mediated defense in response to Xcv effector proteins is typically accompanied by a programmed cell death response referred to as the hypersensitive response (HR). AvrBs3 is one Avr protein that R proteins recognize and is a member of a Xanthomonas family of highly conserved proteins (Schornack et al. (2006) J. Plant Physiol. 163:256). The central region of AvrBs3 consists of 17.5 tandem near-perfect 34-amino-acid (aa) repeat units that determine avirulence specificity (Herbers et al. (1992) Nature 356:172). AvrBs3 contains also nuclear localization signals (NLSs) and an acidic transcriptional activation domain (AD) (Szurek et al. (2001) Plant J. 26:523; Szurek et al. (2002) Mol. Microbiol. 46:13), similar to eukaryotic transcription factors, and induces host gene transcription (Marois et al. (2002) Mol Plant-Microbe Interact. 15:637-646). Mutations in the NLS or AD of AvrBs3 abolish pathogen recognition by the matching pepper R gene Bs3 (Szurek et al. (2001) Plant J. 26:523; Van den Ackerveken et al. (1996) Cell 87:1307) suggesting that recognition involves transcriptional activation of host genes.
The isolation to the Bs3 gene from pepper would provide researchers with the opportunity to further study this recognition process while providing an R gene that can be used to produce transgenic plants having increased resistance to phytopathogens.
The present invention provides an isolated resistance (R) gene, the Bs3 gene from pepper (Capsicum annuum). The Bs3 gene is known to confer upon a plant resistance to the bacterial pathogen, Xanthomonas campestris pv. vesicatoria. As disclosed hereinbelow, transient co-expression of the Bs3 and avrBs3 genes in Nicotiana benthamiana leaves triggered the hypersensitive response (HR) in the leaves. In addition, the invention provides as second allele of the Bs3 gene, referred to as the Bs3-E allele, which triggers HR when co-expressed in N. benthamiana leaves with AvrBs3-derivative, AvrBs3Δrep16.
Thus, the invention provides isolated nucleic acid molecules comprising nucleotide sequences of two alleles of the Bs3 gene. Such nucleic acid molecules include both cDNA sequences and genomic sequences comprising full-length, coding sequences. Both alleles encode amino acid sequences that are homologous to the amino acid sequences of known flavin-dependent monooxygenases.
The invention further provides methods for increasing the resistance of a plant to a plant pathogen. Such methods involve transforming a plant with a nucleotide molecule of the present invention comprising a nucleotide sequence that encodes a Bs3 protein and an operably linked promoter that drives expression in a plant. Such plants have increased resistance to a plant pathogen.
The invention further provides isolated nucleic acid molecules comprising promoter sequences of the Bs3 gene. Such isolated nucleic acid molecules can be operably linked to a gene of interest for expression of the gene in a plant. Thus, the invention provides methods for expressing or increasing the expression of a protein or RNA of interest in a plant involving transforming a plant with a polynucleotide construct that comprises a promoter sequence of the invention operably linked to a gene of interest that encodes the protein or RNA of interest.
Additionally provided are plants, plant parts, seeds, plant cells and other non-human host cells transformed with the isolated nucleic acid molecules of the present invention and the proteins or polypeptides encoded by the coding sequences of the present invention.
The nucleotide and amino acid sequences listed in the accompanying sequence listing are shown using standard letter abbreviations for nucleotide bases, and three-letter code for amino acids. The nucleotide sequences follow the standard convention of beginning at the 5′ end of the sequence and proceeding forward (i.e., from left to right in each line) to the 3′ end. Only one strand of each nucleic acid sequence is shown, but the complementary strand is understood to be included by any reference to the displayed strand. The amino acid sequences follow the standard convention of beginning at the amino terminus of the sequence and proceeding forward (i.e., from left to right in each line) to the carboxy terminus.
SEQ ID NO: 1 sets forth the full-length coding sequence of the Bs3 allele of the Bs3 gene.
SEQ ID NO: 2 sets forth the Bs3 amino acid sequence that is encoded by SEQ ID NO: 1.
SEQ ID NO: 3 sets forth the full-length coding sequence of the Bs3 allele of the Bs3 gene minus the stop codon. Nucleotides 1-1026 of SEQ ID NO: 3 correspond to nucleotides 1-1026 of SEQ ID NO: 1. If desired, a stop codon can be added to the 3′ end of the nucleotide sequence of SEQ ID NO: 3 or any other coding sequence that lacks a stop codon. Such stop codons include, for example, TAA, TAG, and TGA.
SEQ ID NO: 4 sets forth the genomic sequence of the Bs3 allele of the Bs3 gene.
SEQ ID NO: 5 sets forth the nucleotide sequence of the promoter of the Bs3 allele of the Bs3 gene and corresponds to nucleotides 1-1087 of SEQ ID NO: 4.
SEQ ID NO: 6 sets forth a 344 bp fragment of the promoter of the Bs3 allele of the Bs3 gene. This fragment consists of the final 344 bp of the promoter sequence set forth in SEQ ID NO: 5.
SEQ ID NO: 7 sets forth a 166 bp fragment of the promoter of the Bs3 allele of the Bs3 gene. This fragment consists of the final 166 bp of the promoter sequence set forth in SEQ ID NO: 5.
SEQ ID NO: 8 sets forth a 90 bp fragment of the promoter of the Bs3 allele of the Bs3 gene. This fragment consists of the final 90 bp of the promoter sequence set forth in SEQ ID NO: 5.
SEQ ID NO: 9 sets forth the full-length coding sequence of the Bs3-E allele of the Bs3 gene.
SEQ ID NO: 10 sets forth the Bs3-E amino acid sequence that is encoded by SEQ ID NO: 9.
SEQ ID NO: 11 sets forth the full-length coding sequence of the Bs3-E allele of the Bs3 gene minus the stop codon. Nucleotides 1-1026 of SEQ ID NO: 11 correspond to nucleotides 1-1026 of SEQ ID NO: 9. If desired, a stop codon can be added to the 3′ end of the nucleotide sequence of SEQ ID NO: 3 or any other coding sequence that lacks a stop codon. Such stop codons include, for example, TAA, TAG, and TGA.
SEQ ID NO: 12 sets forth the genomic sequence of the Bs3-E allele of the Bs3 gene.
SEQ ID NO: 13 sets forth the nucleotide sequence of the promoter of the Bs3-E allele of the Bs3 gene and corresponds to nucleotides 1-1100 of SEQ ID NO: 12.
SEQ ID NO: 14 sets forth a 357 bp fragment of the promoter of the Bs3-E allele of the Bs3 gene. This fragment consists of the final 357 bp of the promoter sequence set forth in SEQ ID NO: 13.
SEQ ID NO: 15 sets forth a 179 bp fragment of the promoter of the Bs3-E allele of the Bs3 gene. This fragment consists of the final 179 bp of the promoter sequence set forth in SEQ ID NO: 13.
SEQ ID NO: 16 sets forth a 90 bp fragment of the promoter of the Bs3-E allele of the Bs3 gene. This fragment consists of the final 90 bp of the promoter sequence set forth in SEQ ID NO: 13.
SEQ ID NO: 17 sets forth the consensus sequence for the UPA Box.
SEQ ID NO: 18 sets forth the nucleotide sequence of PCR primer designated as A1-fwd-PR.
SEQ ID NO: 19 sets forth the nucleotide sequence of PCR primer designated as B5-rev-PR.
SEQ ID NO: 20 sets forth the nucleotide sequence of PCR primer designated as final-entry-01-fwd.
SEQ ID NO: 21 sets forth the nucleotide sequence of PCR primer designated as final-entry-02-rev.
SEQ ID NO: 22 sets forth the nucleotide sequence of PCR primer designated as Cand-7-01-fwd.
SEQ ID NO: 23 sets forth the nucleotide sequence of PCR primer designated as Cand-7-01-rev.
SEQ ID NO: 24 sets forth the nucleotide sequence of PCR primer designated as RS-EFrt-F1.
SEQ ID NO: 25 sets forth the nucleotide sequence of PCR primer designated as RS-EFrt-R1.
The present invention discloses the isolation and sequencing of two alleles of an R gene, the Bs3 gene from pepper. The Bs3 gene is known to confer resistance to the bacterial pathogen, Xanthomonas campestris pv. vesicatoria (Xcv). Thus, the present invention provides isolated nucleic acid molecules comprising Bs3 nucleotide sequences. Such nucleotide sequences find use in the production of transformed plants with increased resistance to pathogens, particularly bacterial pathogens, more particularly Xanthomonas spp., even move particularly Xanthomonas campestris, and most particularly Xcv. Accordingly, the present invention provides methods for enhancing or increasing the resistance of a plant to a plant pathogen.
This present invention provides isolated Bs3 polypeptides and Bs3 nucleic acid molecules, including cDNA sequences, gene sequences, and promoter sequences. The prototypical Bs3 sequences are the pepper sequences, and the invention provides for the use of these sequences to produce transgenic plants, such as pepper and tomato plants, having enhanced resistance to diseases cause by Xanthomonas campestris, such as bacterial spot disease.
The nucleotide sequence of the Bs3 allele of the pepper Bs3 gene is set forth in SEQ ID NO: 4. This nucleotide sequence comprises 2 introns and 3 exons and a UPA box in the promoter region. The cDNA sequence is set forth in SEQ ID NO: 1. The open reading frame of the Bs3 gene encodes the 342 amino acid Bs3 protein. The amino acid sequence of the Bs3 protein is set forth in SEQ ID NO: 2. The nucleotide sequence of the 1087 bp, the promoter of the Bs3 allele is set forth in SEQ ID NO: 5. The nucleotide sequences of 5′ truncations of the promoter comprising 344, 166, and 90 bps are set forth in SEQ ID NOS: 6-8, respectively.
The nucleotide sequence of the Bs3-E allele of the pepper Bs3 gene is set forth in SEQ ID NO: 12. Like the Bs3 allele, this nucleotide sequence comprises 2 introns and 3 exons and a UPA box in the promoter region. The cDNA sequence is set forth in SEQ ID NO: 9. The open reading frame encodes the 342 amino acid Bs3-E protein. The amino acid sequence of the Bs3-E protein is set forth in SEQ ID NO: 10. The Bs3-E promoter is set forth in SEQ ID NO: 13. The nucleotide sequences of 5′ truncations of the promoter comprising 357, 179, and 90 bps are set forth in SEQ ID NOS: 14-16, respectively.
Throughout the present disclosure, references to the “Bs3 gene” are intended to encompass both alleles of the Bs3 gene unless stated otherwise or readily apparent from the context. Similarly, reference to the “Bs3 protein” is intended to encompass the proteins encoded by both alleles of the Bs3 gene unless stated otherwise or readily apparent from the context.
In one aspect, the present invention provides isolated nucleic acid molecules comprising nucleotide sequences encoding the Bs3 protein. Such isolated nucleic acid molecules find use in methods for expressing, or increasing the expression of, the Bs3 protein in a plant, plant part, plant cell, or other non-human host cell. Given that the Bs3 protein is homologous to known FMOs, expressing or increasing the expression of the Bs3 protein in the plant, plant part, plant cell, or other non-human host cell will not only lead to an increase in the level of the Bs3 protein but likely also cause an increase in FMO activity in the plant, plant part, plant cell, or other non-human host cell.
For expression of the Bs3 protein in a plant or plant cells, the methods of the invention involve transforming a plant with a polynucleotide of the present invention that encodes the Bs3 protein. Such an isolated nucleotide molecule can be operably linked to a promoter that drives expression in a plant cell. Any promoter known in the art can be used in the methods of the invention including, but not limited to, the pathogen-inducible promoters, wound-inducible promoters, tissue-preferred promoters, and chemical-regulated promoters. The choice of promoter will depend on the desired timing and location of expression in the transformed plant or other factors. In one embodiment of the invention, the native Bs3 promoter—either in its native genomic linkage to the downstream Bs3 gene sequences or as part of a recombinant nucleic acid molecule further comprising a Bs3 coding sequence—is employed to increase the expression of the Bs3 protein in a plant in response to the presence of Xcv on the plant or the introduction of the AvrBs3 protein to the plant or co-expression of a nucleic acid molecule encoding AvrBs3 in the plant. It is recognized that such an increase in the Bs3 protein in the leaves of a plant will trigger HR in the leaves. In a preferred embodiment of the invention, the promoter is the Bs3 promoter comprising the nucleotide sequence set forth in SEQ ID NO: 5 or one of the truncated Bs3 promoters comprising the nucleotide sequences set forth in SEQ ID NOS: 6 and 7.
The invention further provides methods for increasing the resistance of a plant to at least one plant pathogen. The methods involve transforming at least one plant cell with a nucleotide molecule of the invention encoding the Bs3 protein. The methods can further involve regenerating the transformed plant cell into a transformed plant. In one embodiment of the invention, the isolated nucleotide molecule comprises the Bs3 gene sequence set forth in SEQ ID NO: 4. It is recognized that the nucleotide sequence of the Bs3 gene that is set forth in SEQ ID NO: 4 comprises the promoter of the Bs3 gene, and therefore, no additional promoter is required for expression in a plant of interest. It is further recognized that not all of the 1087 bp that is 5′ of the translation start in SEQ ID NO: 4 is required to direct pathogen-inducible (or AvrBs3-inducible) gene expression in a plant. It is further recognized that the Bs3 promoter is functional for plant pathogen-inducible gene expression when the first 783 or 921 bp from the 5′ end of SEQ ID NO: 4 is omitted from a nucleotide molecule comprising the nucleotide sequence set forth in SEQ ID NO:4. In other embodiments, an isolated nucleic acid molecule of the invention is operably linked to a promoter that is capable of driving gene expression in a plant. In such embodiments, the isolated nucleotide molecule encodes the Bs3 protein. Preferably, the promoter is a pathogen-inducible promoter, particularly one the drives expression in response to a pathogen of interest or part or component thereof (e.g., an Avr protein). Preferred promoters include, for example, the Bs3 promoter set forth in SEQ ID NO: 5 and the truncations of the Bs3 promoter set forth in SEQ ID NOS: 6 and 7. Such preferred promoters comprise the Bs3 UPA box that corresponds to nucleotides 968-982 of SEQ ID NO: 5, nucleotides 225-239 of SEQ ID NO: 6, and nucleotides 47-61 of SEQ ID NO: 7.
Other preferred promoters include any functional fragments of the Bs3 promoter set forth in SEQ ID NO: 5 that comprise the Bs3 UPA box set forth in nucleotides 968-982 of SEQ ID NO: 5. Particularly preferred are those functional fragments of the Bs3 promoter that are truncations of the Bs3 promoter, particularly 5′ truncations, including, but not limited to, the truncations of the Bs3 promoter set forth in SEQ ID NOS: 6 and 7. The present invention additionally encompasses the Bs3 UPA box comprising nucleotides 968-982 of SEQ ID NO: 5.
In addition to the Bs3 promoter and functional fragments thereof, the invention further provides the Bs3-E promoter and functional fragments thereof. The Bs3-E promoter and functional fragments thereof find use in the methods disclosed herein. The functional fragments of the Bs3-E promoter comprise promoter activity. Preferrably, such functional fragments are pathogen-inducible promoters. Such pathogen-inducible promoters are capably of driving or increasing the expression of an operably linked polynucleotide in response to a pathogen of interest or part or component thereof (e.g., an Avr protein). Preferred promoters include, for example, the Bs3-E promoter set forth in SEQ ID NO: 13 and the truncations of the Bs3-E promoter set forth in SEQ ID NOS: 14 and 15. Such preferred promoters comprise the Bs3-E UPA box that corresponds to nucleotides 968-995 of SEQ ID NO: 13, nucleotides 225-252 of SEQ ID NO: 14, and nucleotides 47-74 of SEQ ID NO: 15.
Other preferred promoters include any functional fragments of the Bs3-E promoter set forth in SEQ ID NO: 13 that comprise the Bs3-E UPA box set forth in nucleotides 968-995 of SEQ ID NO: 13. When compared to the Bs3 UPA box (TATATAAACCTAACC; nucleotides 968-982 of SEQ ID NO: 5), the Bs3-E UPA box has an insertion of 13 additional nucleotides (TATATAAACCTctctattccactaAACC; insertion lower case; nucleotides 968-995 of SEQ ID NO: 13) Particularly preferred are those functional fragments of the Bs3-E promoter that are truncations of the Bs3-E promoter, particularly 5′ truncations, including, but not limited to the truncations of the Bs3-E promoter set forth in SEQ ID NOS: 14 and 15. The present invention additionally encompasses the Bs3-E UPA box comprising nucleotides 968-995 of SEQ ID NO: 13.
The methods for increasing the resistance of a plant to at least one plant pathogen find use in increasing or enhancing the resistance of plants, particularly agricultural or crop plants, to plant pathogens. The methods of the invention can be used with any plant species including monocots and dicots. Preferred plants include Solanaceous plants, such as, for example, pepper and tomato.
In a preferred embodiment of the methods for increasing the resistance of a plant to at least one plant pathogen, the plant pathogen is Xcv. However, the methods of the invention are not limited to the plant pathogen, Xcv. Other plant pathogens include, but are not limited to, other xanthomonads. By “xanthomonads” is intended bacterial species that are members of the genus Xanthomonas.
In other embodiments, the methods can involve additional R genes to increase plant resistance to a single plant pathogen or increase plant resistant to different plant pathogen. For example, a pepper plant comprising the Bs2 resistance gene can be transformed with an isolated nucleotide molecule encoding the Bs3 gene as described above to increase resistance to Xcv. Alternatively, the plant can be transformed with both the Bs2 and Bs3 genes either separately or as part of a single polynucleotide construct. The nucleotide sequences of the Bs2 have been previously disclosed. See, U.S. Pat. Nos. 6,262,343 and 6,762,285; each of which is herein incorporated by reference.
In another embodiment, the methods can involve transforming a plant with a pathogen-inducible promoter operably linked to a polynucleotide of the present invention that encodes the Bs3 protein. The invention does not depend on a particular pathogen-inducible promoter. Preferably, the pathogen-inducible promoter is one that directs very little or no expression of the operably linked Bs3 polynucleotide in the absence or the inducing pathogen or inducing part or component thereof. It is recognized that the by placing a Bs3 polynucleotide under the control of such a pathogen-inducible promoter, the expression of the Bs3 polynucleotide can be induced in plant in response to any pathogen or pathogens to which that promoter is responsive. It is further recognized expression in a plant of the Bs3 protein from such a Bs3 polynucleotide can induce cell death. In a preferred embodiment of the invention, expression of the Bs3 protein from a pathogen-inducible promoter that is active at the site, or in vicinity, of the pathogen attack on the plant causes cell death at the site, or in vicinity, of the pathogen attack and that such cell death inhibits or otherwise delays the development of plant disease.
The Bs3 coding sequences of the invention find further use in methods for causing cell death in a plant part of interest. Such a plant part of interest can be, for example, a plant cell or cell, a plant tissue, a plant organ, a seed, or part thereof. Expression of Bs3 coding sequence in plant part of interest leads to the production of the Bs3 protein, a flavin-dependent monooxygenase, which can cause the death of the plant part of interest. Such methods can be used, for example, to make a male sterile plant by expressing a Bs3 coding sequence under the direction of an operably linked promoter that drives gene expression in pollen cells or other cells or tissues that give rise to, or support, the growth and development of pollen, particularly male reproductive tissues. Such male sterile plants find use in the production of hybrid crop plants be reducing the need to remove male reproductive parts or organs from the maternal parent plant of the hybrid crop plant.
The methods for causing cell death in a plant part of interest involve transforming a plant cell with polynucleotide construct comprising a promoter that drives expression in a plant cell operably linked a Bs3 coding sequence of the present invention. Such a promoter directs expression of the Bs3 in the plant part of interest. Preferably, the promoter is one the directs expression little or no expression in plant cells or parts other than the plant part of interest where cell death is desired. The methods further involve regenerating the transformed plant cell into a transformed plant. In the transformed plant, cell death occurs in the plant part of interest upon expression of the Bs3 coding sequence of the present invention in the plant part of interest. Cell death can occur in all cells in the plant part of interest or can occur in a subset of cells within the plant part of interest or even in a single cell.
In another aspect, the invention provides isolated nucleic acid molecules comprising the nucleotide sequences of regions of the Bs3 gene that control or regulate gene expression in a plant, otherwise known as promoters. Such promoters find use in controlling the expression of the Bs3 gene or any other gene of interest in a plant, plant cell or plant part. It is recognized that the promoters of the invention are inducible promoters that direct little or no expression of operably linked nucleotide sequences in the absence of Xcv or the AvrBs3 but provide high-level expression in the presence of avrBs3-expressing Xcv. The promoters of the invention include those comprising the nucleotide sequences set forth SEQ ID NOS: 5-7 and 13-15, and fragments and variants thereof that comprise the pathogen-inducible promoter activity of the promoters comprising the nucleotide sequences set forth SEQ ID NOS: 5-7 and 13-15.
Thus, the invention further provides methods for expressing a gene of interest in a plant, plant part, or plant cell. The methods involve operably linking a promoter of the present invention to a gene of interest so as to produce a polynucleotide construct. Such genes of interest will depend on the desired outcome and can comprise nucleotide sequences that encode proteins and/or RNAs of interest. The methods further involve transforming at least one plant cell with the polynucleotide construct. The methods can additionally involve regenerating the transformed plant cell into a transformed plant. The gene of interest is expressed when the promoter is induced after exposing the plant, plant part, or plant cell to Xcv and/or AvrBs3. Based on studies of the expression of the Bs3 transcripts, it is expected the expression of the gene of interest will be detectable within about 6 hours after Xcv infection or treatment with AvrBs3, peak at about 12 hours after infection and remain at that level until about 24 hours after infection or treatment. Expression of the gene of interest can be determined by any method known in the art for measuring the expression of a gene at the RNA, protein, and/or metabolic (e.g., enzyme activity) levels. Methods of monitoring change in gene expression include, for example, Northern blotting, Western blotting, and enzyme assays.
By “gene of interest” is intended any nucleotide sequence that can be expressed when operable linked to a promoter. A gene of interest of the present invention may, but need not, encode a protein. Unless stated otherwise or readily apparent from the context, when a gene of interest of the present invention is said to be operably linked to a promoter of the invention, the gene of interest does not by itself comprise a functional promoter.
In another aspect, the present invention provides a method for expressing a gene in a plant, plant part, or plant cell. The method makes use of the ability of AvrBs3 to induce the expression of genes of interest operably linked to the Bs3 promoter and can be used to achieve high-level expression of the gene of interest in the plant, or part or cell thereof. The method involves a first polynucleotide construct and a second polynucleotide construct that can be linked on the same nucleic acid molecule or unlinked as two separate nucleic acid molecules. The first polynucleotide construct comprises a first promoter of the invention operably linked to the coding sequence of AvrBs3 (EMBL Accession X16130.1; GenBank Accession CAA34257). The second polynucleotide construct comprises a second promoter of the invention operably linked to a gene of interest. The first promoter can be any promoter that is capable of directing expression of a AvrBs3 coding sequence in a plant or part or cell thereof including, but not limited to, a constitutive promoter, a wound-inducible promoter, a pathogen-inducible promoter, a chemical-regulated promoter, a chemical-inducible promoter, a tissue-preferred promoter, and a Bs3 promoter of the present invention. The second promoter is a Bs3 promoter of the present invention. The method involves producing a transformed or transgenic plant that comprises both the first and second polynucleotide constructs.
In one embodiment of this method of the invention, the first promoter is a chemical-inducible promoter and the transformed plant comprises both the first and second polynucleotide constructions as described above. After such a transformed plant is first exposed to the chemical inducer, the increase in the expression of AvrBs3 coding sequences from the first construct will lead to production of AvrBs3 protein within cells of the plant and such AvrBs3 protein will induce the expression of the gene of interest in the second polynucleotide construct leading to high-level expression of gene product of the gene of interest. Such a gene product can be, for example, a protein or an RNA.
In another embodiment of this method of the invention, the first promoter is a Bs3 promoter of the invention, and the transformed plant comprises both the first and second polynucleotide constructions as described above. After such a transformed plant is first exposed to Xcv or AvrBs3, the increase in the expression of AvrBs3 coding sequences from the first construct will lead to production of AvrBs3 protein within cells of the plant and such AvrBs3 protein will induce further the expression of the gene of interest in the second polynucleotide construct leading to high-level expression of gene product of the gene of interest. Such a gene product can be, for example, a protein or an RNA.
A plant comprising both the first and second polynucleotide constructs can be produced by any method know in the art. For example, such a plant can be produced by the steps of (1) transforming a the plant cell with a single nucleic acid molecule comprising both constructs, or by co-transforming the cell with the first and second polynucleotide constructs, each on a separate nucleic acid molecule, and (2) regenerating a transformed plant that comprises both the first and second polynucleotide constructs. Alternatively, a first transformed plant can be produced that comprises the first polynucleotide construct. The second polynucleotide construct is introduced into a cell of the first transformed plant and a second transformed plant is regenerated therefrom which comprises both the first and second polynucleotide constructs. It is recognized that in such a sequential transformation, the second polynucleotide construct can be introduced into a plant cell to produce a first transformed plant followed by introduction of the first polynucleotide construct into a cell of the first plant and the subsequent production of a second transformed plant comprising both constructs. Another alternative involves sexual reproduction to combine the two constructs in a single plant. In this alternative, a first transformed plant that comprises the first polynucleotide construct is crossed to a second transformed plant that comprises the second polynucleotide construct and allowed to produce progeny or seeds that comprise both the first and second polynucleotide constructs.
The invention encompasses isolated or substantially purified polynucleotide or protein compositions. An “isolated” or “purified” polynucleotide or protein, or biologically active portion thereof, is substantially or essentially free from components that normally accompany or interact with the polynucleotide or protein as found in its naturally occurring environment. Thus, an isolated or purified polynucleotide or protein is substantially free of other cellular material or culture medium when produced by recombinant techniques, or substantially free of chemical precursors or other chemicals when chemically synthesized. Optimally, an “isolated” polynucleotide is free of sequences (optimally protein encoding sequences) that naturally flank the polynucleotide (i.e., sequences located at the 5′ and 3′ ends of the polynucleotide) in the genomic DNA of the organism from which the polynucleotide is derived. For example, in various embodiments, the isolated polynucleotide can contain less than about 5 kb, 4 kb, 3 kb, 2 kb, 1 kb, 0.5 kb, or 0.1 kb of nucleotide sequence that naturally flank the polynucleotide in genomic DNA of the cell from which the polynucleotide is derived. A protein that is substantially free of cellular material includes preparations of protein having less than about 30%, 20%, 10%, 5%, or 1% (by dry weight) of contaminating protein. When the protein of the invention or biologically active portion thereof is recombinantly produced, optimally culture medium represents less than about 30%, 20%, 10%, 5%, or 1% (by dry weight) of chemical precursors or non-protein-of-interest chemicals.
Fragments and variants of the disclosed polynucleotides and proteins encoded thereby are also encompassed by the present invention. By “fragment” is intended a portion of the polynucleotide or a portion of the amino acid sequence and hence protein encoded thereby. Fragments of a polynucleotides comprising coding sequences may encode protein fragments that retain biological activity of the native protein and hence flavin-dependent monooxygenases activity Fragments of polynucleotide comprising promoter sequences retain biological activity of the native promoter an hence retain Bs3 promoter activity. Alternatively, fragments of a polynucleotide that are useful as hybridization probes generally do not encode proteins that retain biological activity or do not retain promoter activity. Thus, fragments of a nucleotide sequence may range from at least about 20 nucleotides, about 50 nucleotides, about 100 nucleotides, and up to the full-length polynucleotide of the invention.
Unless stated otherwise or obvious from the context, “Bs3 promoter activity” is intended to mean the promoter activity of the Bs3 promoter or the Bs3-E promoter as disclosed herein. Likewise, unless stated otherwise or obvious from the context, the terms “Bs3 polynucleotide” and “Bs3 protein” (and similar terms) are intended to mean a polynucleotide of the Bs3 gene or the Bs3-E gene and the Bs3 protein or Bs3-E protein, respectively. Unless stated otherwise or obvious from the context, such terms also encompass variants and fragments of the Bs3 and Bs3-E nucleotide and amino acid sequences disclosed herein.
A fragment of a Bs3 polynucleotide that encodes a biologically active portion of a Bs3 protein of the invention will encode at least 15, 25, 30, 50, 100, 150, 200, 250, or 300 contiguous amino acids, or up to the total number of amino acids present in a full-length Bs3 protein of the invention (for example, 342 amino acids for both SEQ ID NOS: 2 and 10). Fragments of a Bs3 polynucleotide that are useful as hybridization probes or PCR primers generally need not encode a biologically active portion of a Bs3 protein or Bs3 promoter.
Thus, a fragment of a Bs3 polynucleotide may encode a biologically active portion of a Bs3 protein or Bs3 promoter, or it may be a fragment that can be used as a hybridization probe or PCR primer using methods disclosed below. A biologically active portion of a Bs3 protein can be prepared by isolating a portion of one of the Bs3 polynucleotides of the invention, expressing the encoded portion of the Bs3 protein (e.g., by recombinant expression in vitro), and assessing the activity of the encoded portion of the Bs3 protein. A biologically active portion of a Bs3 promoter can be prepared by isolating a portion of one of the Bs3 polynucleotides of the invention that comprises the Bs3 promoter, operably linking the portion of the promoter to nucleotide sequence (e.g. one that encodes a reporter gene) and assessing the activity of the promoter portion by monitoring the expression of the nucleotide sequence when the operably linked promoter portion and nucleotide sequence are introduced into a plant cell. Polynucleotides that are fragments of a Bs3 nucleotide sequence comprise at least 16, 20, 50, 75, 100, 125, 150, 175, 200, 250, 300, 350, 400, 450, 500, 550, 600, 650, 700, 800, 900, 1000, 1100, 1200, 1300, 1400, 1500, 2000, 2500, or 3000 contiguous nucleotides, or up to the number of nucleotides present in a full-length Bs3 polynucleotide disclosed herein (for example, 1029, 1026, 3331, 1087, 344, 166, 90, 1029, 1026, 3344, 1100, 357, 179, and 90 nucleotides for SEQ ID NOS: 1, 3-9, and 11-16, respectively).
“Variants” is intended to mean substantially similar sequences. For polynucleotides, a variant comprises a polynucleotide having deletions (i.e., truncations) at the 5′ and/or 3′ end; deletion and/or addition of one or more nucleotides at one or more internal sites in the native polynucleotide; and/or substitution of one or more nucleotides at one or more sites in the native polynucleotide. As used herein, a “native” polynucleotide or polypeptide comprises a naturally occurring nucleotide sequence or amino acid sequence, respectively. For polynucleotides, conservative variants include those sequences that, because of the degeneracy of the genetic code, encode the amino acid sequence of one of the Bs3 polypeptides of the invention. Naturally occurring allelic variants such as these can be identified with the use of well-known molecular biology techniques, as, for example, with polymerase chain reaction (PCR) and hybridization techniques as outlined below. Variant polynucleotides also include synthetically derived polynucleotides, such as those generated, for example, by using site-directed mutagenesis but which still encode a Bs3 protein of the invention. Generally, variants of a particular polynucleotide of the invention will have at least about 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% or more sequence identity to that particular polynucleotide as determined by sequence alignment programs and parameters as described elsewhere herein.
Variants of a particular polynucleotide of the invention (i.e., the reference polynucleotide) can also be evaluated by comparison of the percent sequence identity between the polypeptide encoded by a variant polynucleotide and the polypeptide encoded by the reference polynucleotide. Thus, for example, an isolated polynucleotide that encodes a polypeptide with a given percent sequence identity to the polypeptide of SEQ ID NO: 2 and/or SEQ ID NO: 10 are disclosed. Percent sequence identity between any two polypeptides can be calculated using sequence alignment programs and parameters described elsewhere herein. Where any given pair of polynucleotides of the invention is evaluated by comparison of the percent sequence identity shared by the two polypeptides they encode, the percent sequence identity between the two encoded polypeptides is at least about 60%, 65%, 70%, 75%, 80%, 85%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% or more sequence identity.
“Variant” protein is intended to mean a protein derived from the native protein by deletion (so-called truncation) of one or more amino acids at the N-terminal and/or C-terminal end of the native protein; deletion and/or addition of one or more amino acids at one or more internal sites in the native protein; or substitution of one or more amino acids at one or more sites in the native protein. Variant proteins encompassed by the present invention are biologically active, that is they continue to possess the desired biological activity of the native protein, that is, flavin-dependent monooxygenase activity as described herein. Such variants may result from, for example, genetic polymorphism or from human manipulation. Biologically active variants of a native Bs3 protein of the invention will have at least about 60%, 65%, 70%, 75%, 80%, 85%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% or more sequence identity to the amino acid sequence for the native protein as determined by sequence alignment programs and parameters described elsewhere herein. A biologically active variant of a protein of the invention may differ from that protein by as few as 1-15 amino acid residues, as few as 1-10, such as 6-10, as few as 5, as few as 4, 3, 2, or even 1 amino acid residue.
The proteins of the invention may be altered in various ways including amino acid substitutions, deletions, truncations, and insertions. Methods for such manipulations are generally known in the art. For example, amino acid sequence variants and fragments of the Bs3 proteins can be prepared by mutations in the DNA. Methods for mutagenesis and polynucleotide alterations are well known in the art. See, for example, Kunkel (1985) Proc. Natl. Acad. Sci. USA 82:488-492; Kunkel et al. (1987) Methods in Enzymol. 154:367-382; U.S. Pat. No. 4,873,192; Walker and Gaastra, eds. (1983) Techniques in Molecular Biology (MacMillan Publishing Company, New York) and the references cited therein. Guidance as to appropriate amino acid substitutions that do not affect biological activity of the protein of interest may be found in the model of Dayhoff et al. (1978) Atlas of Protein Sequence and Structure (Natl. Biomed. Res. Found., Washington, D.C.), herein incorporated by reference. Conservative substitutions, such as exchanging one amino acid with another having similar properties, may be optimal.
Thus, the genes and polynucleotides of the invention include both the naturally occurring sequences as well as mutant forms. Likewise, the proteins of the invention encompass both naturally occurring proteins as well as variations and modified forms thereof. Such variants will continue to possess the desired Bs3 biological activity, particularly flavin-dependent monooxygenase activity. Obviously, the mutations that will be made in the DNA encoding the variant must not place the sequence out of reading frame and optimally will not create complementary regions that could produce secondary mRNA structure. See, EP Patent Application Publication No. 75,444.
The deletions, insertions, and substitutions of the protein sequences encompassed herein are not expected to produce radical changes in the characteristics of the protein. However, when it is difficult to predict the exact effect of the substitution, deletion, or insertion in advance of doing so, one skilled in the art will appreciate that the effect will be evaluated by routine screening assays. That is, the activity can be evaluated by flavin-dependent monooxygenase activity assays. See, for example, Krueger et al. (2005). Pharmacol. Ther. 106, 357-387; herein incorporated by reference.
Variant polynucleotides and proteins also encompass sequences and proteins derived from a mutagenic and recombinogenic procedure such as DNA shuffling. Strategies for such DNA shuffling are known in the art. See, for example, Stemmer (1994) Proc. Natl. Acad. Sci. USA 91:10747-10751; Stemmer (1994) Nature 370:389-391; Crameri et al. (1997) Nature Biotech. 15:436-438; Moore et al. (1997) J. Mol. Biol. 272:336-347; Zhang et al. (1997) Proc. Natl. Acad. Sci. USA 94:4504-4509; Crameri et al. (1998) Nature 391:288-291; and U.S. Pat. Nos. 5,605,793 and 5,837,458.
The polynucleotides of the invention can be used to isolate corresponding sequences from other organisms, particularly other plants. In this manner, methods such as PCR, hybridization, and the like can be used to identify such sequences based on their sequence homology to the sequences set forth herein. Sequences isolated based on their sequence identity to the entire Bs3 sequences set forth herein or to variants and fragments thereof are encompassed by the present invention. Such sequences include sequences that are orthologs of the disclosed sequences. “Orthologs” is intended to mean genes derived from a common ancestral gene and which are found in different species as a result of speciation. Genes found in different species are considered orthologs when their nucleotide sequences and/or their encoded protein sequences share at least 60%, 70%, 75%, 80%, 85%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or greater sequence identity. Functions of orthologs are often highly conserved among species. Thus, isolated polynucleotides that have Bs3 promoter activity or encode for a Bs3 protein and which hybridize under stringent conditions to at least one of the Bs3 polynucleotides disclosed herein, or to variants or fragments thereof, are encompassed by the present invention.
In a PCR approach, oligonucleotide primers can be designed for use in PCR reactions to amplify corresponding DNA sequences from cDNA or genomic DNA extracted from any plant of interest. Methods for designing PCR primers and PCR cloning are generally known in the art and are disclosed in Sambrook et al. (1989) Molecular Cloning: A Laboratory Manual (2d ed., Cold Spring Harbor Laboratory Press, Plainview, N.Y.). See also Innis et al., eds. (1990) PCR Protocols: A Guide to Methods and Applications (Academic Press, New York); Innis and Gelfand, eds. (1995) PCR Strategies (Academic Press, New York); and Innis and Gelfand, eds. (1999) PCR Methods Manual (Academic Press, New York). Known methods of PCR include, but are not limited to, methods using paired primers, nested primers, single specific primers, degenerate primers, gene-specific primers, vector-specific primers, partially-mismatched primers, and the like.
In hybridization techniques, all or part of a known polynucleotide is used as a probe that selectively hybridizes to other corresponding polynucleotides present in a population of cloned genomic DNA fragments or cDNA fragments (i.e., genomic or cDNA libraries) from a chosen organism. The hybridization probes may be genomic DNA fragments, cDNA fragments, RNA fragments, or other oligonucleotides, and may be labeled with a detectable group such as 32P, or any other detectable marker. Thus, for example, probes for hybridization can be made by labeling synthetic oligonucleotides based on the Bs3 polynucleotides of the invention. Methods for preparation of probes for hybridization and for construction of cDNA and genomic libraries are generally known in the art and are disclosed in Sambrook et al. (1989) Molecular Cloning: A Laboratory Manual (2d ed., Cold Spring Harbor Laboratory Press, Plainview, N.Y.).
For example, the entire Bs3 polynucleotide disclosed herein, or one or more portions thereof, may be used as a probe capable of specifically hybridizing to corresponding Bs3 polynucleotide and messenger RNAs. To achieve specific hybridization under a variety of conditions, such probes include sequences that are unique among Bs3 polynucleotide sequences and are optimally at least about 10 nucleotides in length, and most optimally at least about 20 nucleotides in length. Such probes may be used to amplify corresponding Bs3 polynucleotides from a chosen plant by PCR. This technique may be used to isolate additional coding sequences from a desired plant or as a diagnostic assay to determine the presence of coding sequences in a plant. Hybridization techniques include hybridization screening of plated DNA libraries (either plaques or colonies; see, for example, Sambrook et al. (1989) Molecular Cloning: A Laboratory Manual (2d ed., Cold Spring Harbor Laboratory Press, Plainview, N.Y. ).
Hybridization of such sequences may be carried out under stringent conditions. By “stringent conditions” or “stringent hybridization conditions” is intended conditions under which a probe will hybridize to its target sequence to a detectably greater degree than to other sequences (e.g., at least 2-fold over background). Stringent conditions are sequence-dependent and will be different in different circumstances. By controlling the stringency of the hybridization and/or washing conditions, target sequences that are 100% complementary to the probe can be identified (homologous probing). Alternatively, stringency conditions can be adjusted to allow some mismatching in sequences so that lower degrees of similarity are detected (heterologous probing). Generally, a probe is less than about 1000 nucleotides in length, optimally less than 500 nucleotides in length.
Typically, stringent conditions will be those in which the salt concentration is less than about 1.5 M Na ion, typically about 0.01 to 1.0 M Na ion concentration (or other salts) at pH 7.0 to 8.3 and the temperature is at least about 30° C. for short probes (e.g., 10 to 50 nucleotides) and at least about 60° C. for long probes (e.g., greater than 50 nucleotides). Stringent conditions may also be achieved with the addition of destabilizing agents such as formamide. Exemplary low stringency conditions include hybridization with a buffer solution of 30 to 35% formamide, 1 M NaCl, 1% SDS (sodium dodecyl sulphate) at 37° C., and a wash in 1× to 2×SSC (20×SSC=3.0 M NaCl/0.3 M trisodium citrate) at 50 to 55° C. Exemplary moderate stringency conditions include hybridization in 40 to 45% formamide, 1.0 M NaCl, 1% SDS at 37° C., and a wash in 0.5× to 1×SSC at 55 to 60° C. Exemplary high stringency conditions include hybridization in 50% formamide, 1 M NaCl, 1% SDS at 37° C., and a wash in 0.1×SSC at 60 to 65° C. Optionally, wash buffers may comprise about 0.1% to about 1% SDS. Duration of hybridization is generally less than about 24 hours, usually about 4 to about 12 hours. The duration of the wash time will be at least a length of time sufficient to reach equilibrium.
Specificity is typically the function of post-hybridization washes, the critical factors being the ionic strength and temperature of the final wash solution. For DNA-DNA hybrids, the Tm can be approximated from the equation of Meinkoth and Wahl (1984) Anal. Biochem. 138:267-284: Tm=81.5° C.+16.6 (log M)+0.41 (% GC)−0.61 (% form)−500/L; where M is the molarity of monovalent cations, % GC is the percentage of guanosine and cytosine nucleotides in the DNA, % form is the percentage of formamide in the hybridization solution, and L is the length of the hybrid in base pairs. The Tm is the temperature (under defined ionic strength and pH) at which 50% of a complementary target sequence hybridizes to a perfectly matched probe. Tm is reduced by about 1° C. for each 1% of mismatching; thus, Tm, hybridization, and/or wash conditions can be adjusted to hybridize to sequences of the desired identity. For example, if sequences with ≧90% identity are sought, the Tm can be decreased 10° C. Generally, stringent conditions are selected to be about 5° C. lower than the thermal melting point (Tm) for the specific sequence and its complement at a defined ionic strength and pH. However, severely stringent conditions can utilize a hybridization and/or wash at 1, 2, 3, or 4° C. lower than the thermal melting point (Tm); moderately stringent conditions can utilize a hybridization and/or wash at 6, 7, 8, 9, or 10° C. lower than the thermal melting point (Tm); low stringency conditions can utilize a hybridization and/or wash at 11, 12, 13, 14, 15, or 20° C. lower than the thermal melting point (Tm). Using the equation, hybridization and wash compositions, and desired Tm, those of ordinary skill will understand that variations in the stringency of hybridization and/or wash solutions are inherently described. If the desired degree of mismatching results in a Tm of less than 45° C. (aqueous solution) or 32° C. (formamide solution), it is optimal to increase the SSC concentration so that a higher temperature can be used. An extensive guide to the hybridization of nucleic acids is found in Tijssen (1993) Laboratory Techniques in Biochemistry and Molecular Biology—Hybridization with Nucleic Acid Probes, Part I, Chapter 2 (Elsevier, New York); and Ausubel et al., eds. (1995) Current Protocols in Molecular Biology, Chapter 2 (Greene Publishing and Wiley-Interscience, New York). See Sambrook et al. (1989) Molecular Cloning: A Laboratory Manual (2d ed., Cold Spring Harbor Laboratory Press, Plainview, N.Y.).
It is recognized that the polynucleotide molecules and proteins of the invention encompass polynucleotide molecules and proteins comprising a nucleotide or an amino acid sequence that is sufficiently identical to the nucleotide sequence of SEQ ID NOS: 1 and/or 3, or to the amino acid sequence of SEQ ID NO: 2. It is further recognized that the polynucleotide molecules and proteins of the invention encompass polynucleotide molecules and proteins comprising a nucleotide or an amino acid sequence that is sufficiently identical to the nucleotide sequence of SEQ ID NOS: 9 and/or 11, or to the amino acid sequence of SEQ ID NO: 10. The term “sufficiently identical” is used herein to refer to a first amino acid or nucleotide sequence that contains a sufficient or minimum number of identical or equivalent (e.g., with a similar side chain) amino acid residues or nucleotides to a second amino acid or nucleotide sequence such that the first and second amino acid or nucleotide sequences have a common structural domain and/or common functional activity. For example, amino acid or nucleotide sequences that contain a common structural domain having at least about 45%, 55%, or 65% identity, preferably 75% identity, more preferably 85%, 90%, 95%, 96%, 97%, 98% or 99% identity are defined herein as sufficiently identical.
To determine the percent identity of two amino acid sequences or of two nucleic acids, the sequences are aligned for optimal comparison purposes. The percent identity between the two sequences is a function of the number of identical positions shared by the sequences (i.e., percent identity=number of identical positions/total number of positions (e.g., overlapping positions)×100). In one embodiment, the two sequences are the same length. The percent identity between two sequences can be determined using techniques similar to those described below, with or without allowing gaps. In calculating percent identity, typically exact matches are counted.
The determination of percent identity between two sequences can be accomplished using a mathematical algorithm. A preferred, nonlimiting example of a mathematical algorithm utilized for the comparison of two sequences is the algorithm of Karlin and Altschul (1990) Proc. Natl. Acad. Sci. USA 87:2264, modified as in Karlin and Altschul (1993) Proc. Natl. Acad. Sci. USA 90:5873-5877. Such an algorithm is incorporated into the NBLAST and XBLAST programs of Altschul et al. (1990) J. Mol. Biol. 215:403. BLAST nucleotide searches can be performed with the NBLAST program, score=100, wordlength=12, to obtain nucleotide sequences homologous to the polynucleotide molecules of the invention. BLAST protein searches can be performed with the XBLAST program, score=50, wordlength=3, to obtain amino acid sequences homologous to protein molecules of the invention. To obtain gapped alignments for comparison purposes, Gapped BLAST can be utilized as described in Altschul et al. (1997) Nucleic Acids Res. 25:3389. Alternatively, PSI-Blast can be used to perform an iterated search that detects distant relationships between molecules. See Altschul et al. (1997) supra. When utilizing BLAST, Gapped BLAST, and PSI-Blast programs, the default parameters of the respective programs (e.g., XBLAST and NBLAST) can be used. See http://www.ncbi.nlm.nih.gov. Another preferred, non-limiting example of a mathematical algorithm utilized for the comparison of sequences is the algorithm of Myers and Miller (1988) CABIOS 4:11-17. Such an algorithm is incorporated into the ALIGN program (version 2.0), which is part of the GCG sequence alignment software package. When utilizing the ALIGN program for comparing amino acid sequences, a PAM 120 weight residue table, a gap length penalty of 12, and a gap penalty of 4 can be used. Alignment may also be performed manually by inspection.
Unless otherwise stated, sequence identity/similarity values provided herein refer to the value obtained using the full-length sequences of the invention and using multiple alignment by mean of the algorithm Clustal W (Nucleic Acid Research, 22(22):4673-4680, 1994) using the program AlignX included in the software package Vector NTI Suite Version 7 (InforMax, Inc., Bethesda, Md., USA) using the default parameters; or any equivalent program thereof. By “equivalent program” is intended any sequence comparison program that, for any two sequences in question, generates an alignment having identical nucleotide or amino acid residue matches and an identical percent sequence identity when compared to the corresponding alignment generated by CLUSTALW (Version 1.83) using default parameters (available at the European Bioinformatics Institute website: http://www.ebi.ac.uk/Tools/clustalw/index.html).
The use of the term “polynucleotide” is not intended to limit the present invention to polynucleotides comprising DNA. Those of ordinary skill in the art will recognize that polynucleotides, can comprise ribonucleotides and combinations of ribonucleotides and deoxyribonucleotides. Such deoxyribonucleotides and ribonucleotides include both naturally occurring molecules and synthetic analogues. The polynucleotides of the invention also encompass all forms of sequences including, but not limited to, single-stranded forms, double-stranded forms, hairpins, stem-and-loop structures, and the like.
The Bs3 polynucleotide of the invention comprising Bs3 protein coding sequences can be provided in expression cassettes for expression in the plant or other organism or non-human host cell of interest. The cassette will include 5′ and 3′ regulatory sequences operably linked to a Bs3 polynucleotide of the invention. “Operably linked” is intended to mean a functional linkage between two or more elements. For example, an operable linkage between a polynucleotide or gene of interest and a regulatory sequence (i.e., a promoter) is functional link that allows for expression of the polynucleotide of interest. Operably linked elements may be contiguous or non-contiguous. When used to refer to the joining of two protein coding regions, by operably linked is intended that the coding regions are in the same reading frame. The cassette may additionally contain at least one additional gene to be cotransformed into the organism. Alternatively, the additional gene(s) can be provided on multiple expression cassettes. Such an expression cassette is provided with a plurality of restriction sites and/or recombination sites for insertion of the Bs3 polynucleotide to be under the transcriptional regulation of the regulatory regions. The expression cassette may additionally contain selectable marker genes.
Likewise, the Bs3 promoter sequence of the invention can be provided in expression cassettes for expression in the plant or other organism or non-human host cell of interest. The cassette will include 3′ regulatory sequences operably linked to a polynucleotide of gene of interest. The cassette may optionally additional 5′ regulatory sequences. The Bs3 promoter sequence will be operably linked to the polynucleotide or gene of interest as described above. The cassette may additionally contain at least one additional gene to be cotransformed into the organism. Alternatively, the additional gene(s) can be provided on multiple expression cassettes. Such an expression cassette is provided with a plurality of restriction sites and/or recombination sites and may additionally contain selectable marker genes.
The expression cassette will include in the 5′-3′ direction of transcription, a transcriptional and translational initiation region (i.e., a promoter), a Bs3 polynucleotide of the invention, and a transcriptional and translational termination region (i.e., termination region) functional in plants or other organism or non-human host cell. The regulatory regions (i.e., promoters, transcriptional regulatory regions, and translational termination regions) and/or the Bs3 polynucleotide of the invention may be native/analogous to the host cell or to each other. Alternatively, the regulatory regions and/or the Bs3 polynucleotide of the invention may be heterologous to the host cell or to each other. As used herein, “heterologous” in reference to a sequence is a sequence that originates from a foreign species, or, if from the same species, is substantially modified from its native form in composition and/or genomic locus by deliberate human intervention. For example, a promoter operably linked to a heterologous polynucleotide is from a species different from the species from which the polynucleotide was derived, or, if from the same/analogous species, one or both are substantially modified from their original form and/or genomic locus, or the promoter is not the native promoter for the operably linked polynucleotide. As used herein, a chimeric gene comprises a coding sequence operably linked to a transcription initiation region that is heterologous to the coding sequence.
Likewise, the Bs3 promoter sequence of the invention can be provided in expression cassettes for expression in the plant or other organism or non-human host cell of interest. The cassette will include 3′ regulatory sequences operably linked to a polynucleotide of gene of interest. The cassette may optionally additional 5′ regulatory sequences. The Bs3 promoter sequence will be operably linked to the polynucleotide or gene of interest as described above. The cassette may additionally contain at least one additional gene to be cotransformed into the organism. Alternatively, the additional gene(s) can be provided on multiple expression cassettes. Such an expression cassette is provided with a plurality of restriction sites and/or recombination sites and may additionally contain selectable marker genes.
While it may be optimal to express the Bs3 coding sequences using heterologous promoters, the native promoter sequences or truncations described herein below may be used. Such constructs can change expression levels of the Bs3 protein in the plant or plant cell. Thus, the phenotype of the plant or plant cell can be altered.
The termination region may be native with the transcriptional initiation region, may be native with the operably linked Bs3 polynucleotide of interest, may be native with the plant host, or may be derived from another source (i.e., foreign or heterologous) to the promoter, the Bs3 polynucleotide of interest, the plant host, or any combination thereof. Convenient termination regions are available from the Ti-plasmid of A. tumefaciens, such as the octopine synthase and nopaline synthase termination regions. See also Guerineau et al. (1991) Mol. Gen. Genet. 262:141-144; Proudfoot (1991) Cell 64:671-674; Sanfacon et al. (1991) Genes Dev. 5:141-149; Mogen et al. (1990) Plant Cell 2:1261-1272; Munroe et al. (1990) Gene 91:151-158; Ballas et al. (1989) Nucleic Acids Res. 17:7891-7903; and Joshi et al. (1987) Nucleic Acids Res. 15:9627-9639.
Where appropriate, the polynucleotides may be optimized for increased expression in the transformed plant. That is, the polynucleotides can be synthesized using plant-preferred codons for improved expression. See, for example, Campbell and Gowri (1990) Plant Physiol. 92:1-11 for a discussion of host-preferred codon usage. Methods are available in the art for synthesizing plant-preferred genes. See, for example, U.S. Pat. Nos. 5,380,831, and 5,436,391, and Murray et al. (1989) Nucleic Acids Res. 17:477-498, herein incorporated by reference.
Additional sequence modifications are known to enhance gene expression in a cellular host. These include elimination of sequences encoding spurious polyadenylation signals, exon-intron splice site signals, transposon-like repeats, and other such well-characterized sequences that may be deleterious to gene expression. The G-C content of the sequence may be adjusted to levels average for a given cellular host, as calculated by reference to known genes expressed in the host cell. When possible, the sequence is modified to avoid predicted hairpin secondary mRNA structures.
The expression cassettes may additionally contain 5′ leader sequences. Such leader sequences can act to enhance translation. Translation leaders are known in the art and include: picornavirus leaders, for example, EMCV leader (Encephalomyocarditis 5′ noncoding region) (Elroy-Stein et al. (1989) Proc. Natl. Acad. Sci. USA 86:6126-6130); potyvirus leaders, for example, TEV leader (Tobacco Etch Virus) (Gallie et al. (1995) Gene 165(2):233-238), MDMV leader (Maize Dwarf Mosaic Virus) (Virology 154:9-20), and human immunoglobulin heavy-chain binding protein (BiP) (Macejak et al. (1991) Nature 353:90-94); untranslated leader from the coat protein mRNA of alfalfa mosaic virus (AMV RNA 4) (Jobling et al. (1987) Nature 325:622-625); tobacco mosaic virus leader (TMV) (Gallie et al. (1989) in Molecular Biology of RNA, ed. Cech (Liss, New York), pp. 237-256); and maize chlorotic mottle virus leader (MCMV) (Lommel et al. (1991) Virology 81:382-385). See also, Della-Cioppa et al. (1987) Plant Physiol. 84:965-968.
In preparing the expression cassette, the various DNA fragments may be manipulated, so as to provide for the DNA sequences in the proper orientation and, as appropriate, in the proper reading frame. Toward this end, adapters or linkers may be employed to join the DNA fragments or other manipulations may be involved to provide for convenient restriction sites, removal of superfluous DNA, removal of restriction sites, or the like. For this purpose, in vitro mutagenesis, primer repair, restriction, annealing, resubstitutions, e.g., transitions and transversions, may be involved.
A number of promoters can be used in the practice of the invention. The promoters can be selected based on the desired outcome. The nucleic acids can be combined with constitutive, tissue-preferred, or other promoters for expression in plants. Such constitutive promoters include, for example, the core CaMV 35S promoter (Odell et al. (1985) Nature 313:810-812); rice actin (McElroy et al. (1990) Plant Cell 2:163-171); ubiquitin (Christensen et al. (1989) Plant Mol. Biol. 12:619-632 and Christensen et al. (1992) Plant Mol. Biol. 18:675-689); pEMU (Last et al. (1991) Theor. Appl. Genet. 81:581-588); MAS (Velten et al. (1984) EMBO J. 3:2723-2730); ALS promoter (U.S. Pat. No. 5,659,026), and the like. Other constitutive promoters include, for example, U.S. Pat. Nos. 5,608,149; 5,608,144; 5,604,121; 5,569,597; 5,466,785; 5,399,680; 5,268,463; 5,608,142; and 6,177,611.
Tissue-preferred promoters can be utilized to target enhanced Bs3 expression within a particular plant tissue. Such tissue-preferred promoters include, but are not limited to, leaf-preferred promoters, root-preferred promoters, seed-preferred promoters, and stem-preferred promoters. Tissue-preferred promoters include Yamamoto et al. (1997) Plant J. 12(2):255-265; Kawamata et al. (1997) Plant Cell Physiol. 38(7):792-803; Hansen et al. (1997) Mol Gen Genet. 254(3):337-343; Russell et al. (1997) Transgenic Res. 6(2):157-168; Rinehart et al. (1996) Plant Physiol. 112(3):1331-1341; Van Camp et al. (1996) Plant Physiol. 112(2):525-535; Canevascini et al. (1996) Plant Physiol. 112(2):513-524; Yamamoto et al. (1994) Plant Cell Physiol. 35(5):773-778; Lam (1994) Results Probl. Cell Differ. 20:181-196; Orozco et al. (1993) Plant Mol. Biol. 23(6):1129-1138; Matsuoka et al. (1993) Proc Natl. Acad. Sci. USA 90(20):9586-9590; and Guevara-Garcia et al. (1993) Plant J. 4(3):495-505. Such promoters can be modified, if necessary, for weak expression.
Generally, it will be beneficial to express the gene from an inducible promoter, particularly from a pathogen-inducible promoter. Such promoters include those from pathogenesis-related proteins (PR proteins), which are induced following infection by a pathogen; e.g., PR proteins, SAR proteins, beta-1,3-glucanase, chitinase, etc. See, for example, Redolfi et al. (1983) Neth. J. Plant Pathol. 89:245-254; Uknes et al. (1992) Plant Cell 4:645-656; and Van Loon (1985) Plant Mol. Virol. 4:111-116. See also WO 99/43819, herein incorporated by reference.
Of interest are promoters that are expressed locally at or near the site of pathogen infection. See, for example, Marineau et al. (1987) Plant Mol. Biol. 9:335-342; Matton et al. (1989) Molecular Plant-Microbe Interactions 2:325-331; Somsisch et al. (1986) Proc. Natl. Acad. Sci. USA 83:2427-2430; Somsisch et al. (1988) Mol. Gen. Genet. 2:93-98; and Yang (1996) Proc. Natl. Acad. Sci. USA 93:14972-14977. See also, Chen et al. (1996) Plant J. 10:955-966; Zhang et al. (1994) Proc. Natl. Acad. Sci. USA 91:2507-2511; Warner et al. (1993) Plant J. 3:191-201; Siebertz et al. (1989) Plant Cell 1:961-968; U.S. Pat. No. 5,750,386 (nematode-inducible); and the references cited therein. Of particular interest is the inducible promoter for the maize PRms gene, whose expression is induced by the pathogen Fusarium moniliforme (see, for example, Cordero et al. (1992) Physiol. Mol. Plant. Path. 41:189-200).
Additionally, as pathogens find entry into plants through wounds or insect damage, a wound-inducible promoter may be used in the constructions of the invention. Such wound-inducible promoters include potato proteinase inhibitor (pin II) gene (Ryan (1990) Ann. Rev. Phytopath. 28:425-449; Duan et al. (1996) Nature Biotechnology 14:494-498); wun1 and wun2, U.S. Pat. No. 5,428,148; win1 and win2 (Stanford et al. (1989) Mol. Gen. Genet. 215:200-208); systemin (McGurl et al. (1992) Science 225:1570-1573); WIP1 (Rohmeier et al. (1993) Plant Mol. Biol. 22:783-792; Eckelkamp et al. (1993) FEBS Letters 323:73-76); MPI gene (Corderok et al. (1994) Plant J. 6(2): 141-150); and the like, herein incorporated by reference.
Chemical-regulated promoters can be used to modulate the expression of a gene in a plant through the application of an exogenous chemical regulator. Depending upon the objective, the promoter may be a chemical-inducible promoter, where application of the chemical induces gene expression, or a chemical-repressible promoter, where application of the chemical represses gene expression. Chemical-inducible promoters are known in the art and include, but are not limited to, the maize Tn2-2 promoter, which is activated by benzenesulfonamide herbicide safeners, the maize GST promoter, which is activated by hydrophobic electrophilic compounds that are used as pre-emergent herbicides, and the tobacco PR-1a promoter, which is activated by salicylic acid. Other chemical-regulated promoters of interest include steroid-responsive promoters (see, for example, the glucocorticoid-inducible promoter in Schena et al. (1991) Proc. Natl. Acad. Sci. USA 88:10421-10425 and McNellis et al. (1998) Plant J. 14(2):247-257) and tetracycline-inducible and tetracycline-repressible promoters (see, for example, Gatz et al. (1991) Mol. Gen. Genet. 227:229-237, and U.S. Pat. Nos. 5,814,618 and 5,789,156), herein incorporated by reference.
The expression cassette can also comprise a selectable marker gene for the selection of transformed cells. Selectable marker genes are utilized for the selection of transformed cells or tissues. Marker genes include genes encoding antibiotic resistance, such as those encoding neomycin phosphotransferase II (NEO) and hygromycin phosphotransferase (HPT), as well as genes conferring resistance to herbicidal compounds, such as glufosinate ammonium, bromoxynil, imidazolinones, and 2,4-dichlorophenoxyacetate (2,4-D). Additional selectable markers include phenotypic markers such as β-galactosidase and fluorescent proteins such as green fluorescent protein (GFP) (Su et al. (2004) Biotechnol Bioeng 85:610-9 and Fetter et al. (2004) Plant Cell 16:215-28), cyan florescent protein (CYP) (Bolte et al. (2004) J. Cell Science 117:943-54 and Kato et al. (2002) Plant Physiol 129:913-42), and yellow florescent protein (PhiYFP™ from Evrogen, see, Bolte et al. (2004) J. Cell Science 117:943-54). For additional selectable markers, see generally, Yarranton (1992) Curr. Opin. Biotech. 3:506-511; Christopherson et al. (1992) Proc. Natl. Acad. Sci. USA 89:6314-6318; Yao et al. (1992) Cell 71:63-72; Reznikoff (1992) Mol. Microbiol. 6:2419-2422; Barkley et al. (1980) in The Operon, pp. 177-220; Hu et al. (1987) Cell 48:555-566; Brown et al. (1987) Cell 49:603-612; Figge et al. (1988) Cell 52:713-722; Deuschle et al. (1989) Proc. Natl. Acad. Aci. USA 86:5400-5404; Fuerst et al. (1989) Proc. Natl. Acad. Sci. USA 86:2549-2553; Deuschle et al. (1990) Science 248:480-483; Gossen (1993) Ph.D. Thesis, University of Heidelberg; Reines et al. (1993) Proc. Natl. Acad. Sci. USA 90:1917-1921; Labow et al. (1990) Mol. Cell. Biol. 10:3343-3356; Zambretti et al. (1992) Proc. Natl. Acad. Sci. USA 89:3952-3956; Baim et al. (1991) Proc. Natl. Acad. Sci. USA 88:5072-5076; Wyborski et al. (1991) Nucleic Acids Res. 19:4647-4653; Hillenand-Wissman (1989) Topics Mol. Struc. Biol. 10: 143-162; Degenkolb et al. (1991) Antimicrob. Agents Chemother. 35:1591-1595; Kleinschnidt et al. (1988) Biochemistry 27:1094-1104; Bonin (1993) Ph.D. Thesis, University of Heidelberg; Gossen et al. (1992) Proc. Natl. Acad. Sci. USA 89:5547-5551; Oliva et al. (1992) Antimicrob. Agents Chemother. 36:913-919; Hlavka et al. (1985) Handbook of Experimental Pharmacology, Vol. 78 (Springer-Verlag, Berlin); Gill et al. (1988) Nature 334:721-724. Such disclosures are herein incorporated by reference.
The above list of selectable marker genes is not meant to be limiting. Any selectable marker gene can be used in the present invention.
Numerous plant transformation vectors and methods for transforming plants are available. See, for example, An, G. et al. (1986) Plant Pysiol., 81:301-305; Fry, J., et al. (1987) Plant Cell Rep. 6:321-325; Block, M. (1988) Theor. Appl Genet. 76:767-774; Hinchee, et al. (1990) Stadler. Genet. Symp. 203212.203-212; Cousins, et al. (1991) Aust. J. Plant Physiol. 18:481-494; Chee, P. P. and Slightom, J. L. (1992) Gene. 118:255-260; Christou, et al. (1992) Trends. Biotechnol. 10:239-246; D'Halluin, et al. (1992) Bio/Technol. 10:309-314; Dhir, et al. (1992) Plant Physiol. 99:81-88; Casas et al. (1993) Proc. Nat. Acad. Sci. USA 90:11212-11216; Christou, P. (1993) In Vitro Cell. Dev. Biol.-Plant; 29P: 119-124; Davies, et al. (1993) Plant Cell Rep. 12:180-183; Dong, J. A. and Mchughen, A. (1993) Plant Sci. 91:139-148; Franklin, C. I. and Trieu, T. N. (1993) Plant. Physiol. 102:167; Golovkin, et al. (1993) Plant Sci. 90:41-52; Guo Chin Sci. Bull. 38:2072-2078; Asano, et al. (1994) Plant Cell Rep. 13; Ayeres N. M. and Park, W. D. (1994) Crit. Rev. Plant. Sci. 13:219-239; Barcelo, et al. (1994) Plant. J. 5:583-592; Becker, et al. (1994) Plant. J. 5:299-307; Borkowska et al. (1994) Acta. Physiol Plant. 16:225-230; Christou, P. (1994) Agro. Food. Ind. Hi Tech. 5: 17-27; Eapen et al. (1994) Plant Cell Rep. 13:582-586; Hartman, et al. (1994) Bio-Technology 12: 919923; Ritala, et al. (1994) Plant. Mol. Biol. 24:317-325; and Wan, Y. C. and Lemaux, P. G. (1994) Plant Physiol. 104:3748.
The methods of the invention involve introducing a polynucleotide construct into a plant. By “introducing” is intended presenting to the plant the polynucleotide construct in such a manner that the construct gains access to the interior of a cell of the plant. The methods of the invention do not depend on a particular method for introducing a polynucleotide construct to a plant, only that the polynucleotide construct gains access to the interior of at least one cell of the plant. Methods for introducing polynucleotide constructs into plants are known in the art including, but not limited to, stable transformation methods, transient transformation methods, and virus-mediated methods.
By “stable transformation” is intended that the polynucleotide construct introduced into a plant integrates into the genome of the plant and is capable of being inherited by progeny thereof. By “transient transformation” is intended that a polynucleotide construct introduced into a plant does not integrate into the genome of the plant.
For the transformation of plants and plant cells, the nucleotide sequences of the invention are inserted using standard techniques into any vector known in the art that is suitable for expression of the nucleotide sequences in a plant or plant cell. The selection of the vector depends on the preferred transformation technique and the target plant species to be transformed. In an embodiment of the invention, Bs3 polynucleotide is operably linked to a plant promoter that is known for high-level expression in a plant cell, and this construct is then introduced into a plant that is susceptible to an imidazolinone herbicide and a transformed plant is regenerated. The transformed plant is tolerant to exposure to a level of an imidazolinone herbicide that would kill or significantly injure an untransformed plant. This method can be applied to any plant species; however, it is most beneficial when applied to crop plants.
Methodologies for constructing plant expression cassettes and introducing foreign nucleic acids into plants are generally known in the art and have been previously described. For example, foreign DNA can be introduced into plants, using tumor-inducing (Ti) plasmid vectors. Other methods utilized for foreign DNA delivery involve the use of PEG mediated protoplast transformation, electroporation, microinjection whiskers, and biolistics or microprojectile bombardment for direct DNA uptake. Such methods are known in the art. (U.S. Pat. No. 5,405,765 to Vasil et al.; Bilang et al. (1991) Gene 100: 247-250; Scheid et al., (1991) Mol. Gen. Genet., 228: 104-112; Guerche et al., (1987) Plant Science 52: 111-116; Neuhause et al., (1987) Theor. Appl Genet. 75: 30-36; Klein et al., (1987) Nature 327: 70-73; Howell et al., (1980) Science 208:1265; Horsch et al., (1985) Science 227: 1229-1231; DeBlock et al., (1989) Plant Physiology 91: 694-701; Methods for Plant Molecular Biology (Weissbach and Weissbach, eds.) Academic Press, Inc. (1988) and Methods in Plant Molecular Biology (Schuler and Zielinski, eds.) Academic Press, Inc. (1989). The method of transformation depends upon the plant cell to be transformed, stability of vectors used, expression level of gene products and other parameters.
Other suitable methods of introducing nucleotide sequences into plant cells and subsequent insertion into the plant genome include microinjection as Crossway et al. (1986) Biotechniques 4:320-334, electroporation as described by Riggs et al. (1986) Proc. Natl. Acad. Sci. USA 83:5602-5606, Agrobacterium-mediated transformation as described by Townsend et al., U.S. Pat. No. 5,563,055, Zhao et al., U.S. Pat. No. 5,981,840, direct gene transfer as described by Paszkowski et al. (1984) EMBO J. 3:2717-2722, and ballistic particle acceleration as described in, for example, Sanford et al., U.S. Pat. No. 4,945,050; Tomes et al., U.S. Pat. No. 5,879,918; Tomes et al., U.S. Pat. No. 5,886,244; Bidney et al., U.S. Pat. No. 5,932,782; Tomes et al. (1995) “Direct DNA Transfer into Intact Plant Cells via Microprojectile Bombardment,” in Plant Cell, Tissue, and Organ Culture: Fundamental Methods, ed. Gamborg and Phillips (Springer-Verlag, Berlin); McCabe et al. (1988) Biotechnology 6:923-926); and Lec1 transformation (WO 00/28058). Also see, Weissinger et al. (1988) Ann. Rev. Genet. 22:421-477; Sanford et al. (1987) Particulate Science and Technology 5:27-37 (onion); Christou et al. (1988) Plant Physiol. 87:671-674 (soybean); McCabe et al. (1988) Bio/Technology 6:923-926 (soybean); Finer and McMullen (1991) In Vitro Cell Dev. Biol. 27P:175-182 (soybean); Singh et al. (1998) Theor. Appl. Genet. 96:319-324 (soybean); Datta et al. (1990) Biotechnology 8:736-740 (rice); Klein et al. (1988) Proc. Natl. Acad. Sci. USA 85:4305-4309 (maize); Klein et al. (1988) Biotechnology 6:559-563 (maize); Tomes, U.S. Pat. No. 5,240,855; Buising et al., U.S. Pat. Nos. 5,322,783 and 5,324,646; Tomes et al. (1995) “Direct DNA Transfer into Intact Plant Cells via Microprojectile Bombardment,” in Plant Cell, Tissue, and Organ Culture: Fundamental Methods, ed. Gamborg (Springer-Verlag, Berlin) (maize); Klein et al. (1988) Plant Physiol. 91:440-444 (maize); Fromm et al. (1990) Biotechnology 8:833-839 (maize); Hooykaas-Van Slogteren et al. (1984) Nature (London) 311:763-764; Bowen et al., U.S. Pat. No. 5,736,369 (cereals); Bytebier et al. (1987) Proc. Natl. Acad. Sci. USA 84:5345-5349 (Liliaceae); De Wet et al. (1985) in The Experimental Manipulation of Ovule Tissues, ed. Chapman et al. (Longman, New York), pp. 197-209 (pollen); Kaeppler et al. (1990) Plant Cell Reports 9:415-418 and Kaeppler et al. (1992) Theor. Appl. Genet. 84:560-566 (whisker-mediated transformation); D'Halluin et al. (1992) Plant Cell 4:1495-1505 (electroporation); Li et al. (1993) Plant Cell Reports 12:250-255 and Christou and Ford (1995) Annals of Botany 75:407-413 (rice); Osjoda et al. (1996) Nature Biotechnology 14:745-750 (maize via Agrobacterium tumefaciens); all of which are herein incorporated by reference.
The polynucleotides of the invention may be introduced into plants by contacting plants with a virus or viral nucleic acids. Generally, such methods involve incorporating a polynucleotide construct of the invention within a viral DNA or RNA molecule. It is recognized that the a Bs3 protein of the invention may be initially synthesized as part of a viral polyprotein, which later may be processed by proteolysis in vivo or in vitro to produce the desired recombinant protein. Further, it is recognized that promoters of the invention also encompass promoters utilized for transcription by viral RNA polymerases. Methods for introducing polynucleotide constructs into plants and expressing a protein encoded therein, involving viral DNA or RNA molecules, are known in the art. See, for example, U.S. Pat. Nos. 5,889,191, 5,889,190, 5,866,785, 5,589,367 and 5,316,931; herein incorporated by reference.
In specific embodiments, the Bs3 sequences of the invention can be provided to a plant using a variety of transient transformation methods. Such transient transformation methods include, but are not limited to, the introduction of the Bs3 protein or variants and fragments thereof directly into the plant or the introduction of a Bs3 transcript into the plant. Such methods include, for example, microinjection or particle bombardment. See, for example, Crossway et al. (1986) Mol. Gen. Genet. 202:179-185; Nomura et al. (1986) Plant Sci. 44:53-58; Hepler et al. (1994) Proc. Natl. Acad. Sci. 91: 2176-2180 and Hush et al. (1994) The Journal of Cell Science 107:775-784, all of which are herein incorporated by reference. Alternatively, the polynucleotide can be transiently transformed into the plant using techniques known in the art. Such techniques include viral vector system and Agrobacterium tumefaciens-mediated transient expression as described below.
The cells that have been transformed may be grown into plants in accordance with conventional ways. See, for example, McCormick et al. (1986) Plant Cell Reports 5:81-84. These plants may then be grown, and either pollinated with the same transformed strain or different strains, and the resulting hybrid having constitutive expression of the desired phenotypic characteristic identified. Two or more generations may be grown to ensure that expression of the desired phenotypic characteristic is stably maintained and inherited and then seeds harvested to ensure expression of the desired phenotypic characteristic has been achieved. In this manner, the present invention provides transformed seed (also referred to as “transgenic seed”) having a polynucleotide construct of the invention, for example, an expression cassette of the invention, stably incorporated into their genome.
The present invention may be used for transformation of any plant species, including, but not limited to, monocots and dicots. Examples of plant species of interest include, but are not limited to, peppers (Capsicum spp; e.g., Capsicum annuum, C. baccatum, C. chinense, C. frutescens, C. pubescens, and the like), tomatoes (Lycopersicon esculentum), tobacco (Nicotiana tabacum), eggplant (Solanum melongena), petunia (Petunia spp., e.g., Petunia×hybrida or Petunia hybrida), corn or maize (Zea mays), Brassica sp. (e.g., B. napus, B. rapa, B. juncea), particularly those Brassica species useful as sources of seed oil, alfalfa (Medicago sativa), rice (Oryza sativa), rye (Secale cereale), sorghum (Sorghum bicolor, Sorghum vulgare), millet (e.g., pearl millet (Pennisetum glaucum), proso millet (Panicum miliaceum), foxtail millet (Setaria italica), finger millet (Eleusine coracana)), sunflower (Helianthus annuus), safflower (Carthamus tinctorius), wheat (Triticum aestivum), soybean (Glycine max), tobacco (Nicotiana tabacum), potato (Solanum tuberosum), peanuts (Arachis hypogaea), cotton (Gossypium barbadense, Gossypium hirsutu), sweet potato (Ipomoea batatus), cassaya (Manihot esculenta), coffee (Coffea spp.), coconut (Cocos nucifera), pineapple (Ananas comosus), citrus trees (Citrus spp.), cocoa (Theobroma cacao), tea (Camellia sinensis), banana (Musa spp.), avocado (Persea americana), fig (Ficus casica), guava (Psidium guajava), mango (Mangifera indica), olive (Olea europaea), papaya (Carica papaya), cashew (Anacardium occidentale), macadamia (Macadamia integrifolia), almond (Prunus amygdalus), sugar beets (Beta vulgaris), sugarcane (Saccharum spp.), oats, barley, vegetables, ornamentals, and conifers.
As used herein, the term plant includes plant cells, plant protoplasts, plant cell tissue cultures from which plants can be regenerated, plant calli, plant clumps, and plant cells that are intact in plants or parts of plants such as embryos, pollen, ovules, seeds, leaves, flowers, branches, fruits, roots, root tips, anthers, and the like. Progeny, variants, and mutants of the regenerated plants are also included within the scope of the invention, provided that these parts comprise the introduced polynucleotides.
It is recognized that with these nucleotide sequences, antisense constructions, complementary to at least a portion of the messenger RNA (mRNA) for the Bs3 polynucleotide sequences can be constructed. Antisense nucleotides are constructed to hybridize with the corresponding mRNA. Modifications of the antisense sequences may be made as long as the sequences hybridize to and interfere with expression of the corresponding mRNA. In this manner, antisense constructions having 70%, preferably 80%, more preferably 85% sequence identity to the corresponding antisensed sequences may be used. Furthermore, portions of the antisense nucleotides may be used to disrupt the expression of the target gene. Generally, sequences of at least 50 nucleotides, 100 nucleotides, 200 nucleotides, or greater may be used.
The nucleotide sequences of the present invention may also be used in the sense orientation to suppress the expression of endogenous genes in plants. Methods for suppressing gene expression in plants using nucleotide sequences in the sense orientation are known in the art. The methods generally involve transforming plants with a DNA construct comprising a promoter that drives expression in a plant operably linked to at least a portion of a nucleotide sequence that corresponds to the transcript of the endogenous gene. Typically, such a nucleotide sequence has substantial sequence identity to the sequence of the transcript of the endogenous gene, preferably greater than about 65% sequence identity, more preferably greater than about 85% sequence identity, most preferably greater than about 95% sequence identity. See, U.S. Pat. Nos. 5,283,184 and 5,034,323; herein incorporated by reference.
The invention is drawn to compositions and methods for inducing resistance to plant disease. By “disease resistance” is intended that the plants avoid the disease symptoms that are the outcome of plant-pathogen interactions. That is, pathogens are prevented from causing plant diseases and the associated disease symptoms, or alternatively, the disease symptoms caused by the pathogen is minimized or lessened. Pathogens of the invention include, but are not limited to, viruses or viroids, bacteria, insects, nematodes, fungi, and the like. Viruses include any plant virus, for example, tobacco or cucumber mosaic virus, ringspot virus, necrosis virus, maize dwarf mosaic virus, etc. Fungal pathogens, include but are not limited to, Colletotrichum graminocola, Diplodia maydis, Fusarium graminearum, and Fusarium verticillioides. Specific pathogens for the major crops include: Soybeans: Phytophthora megasperma fsp. glycinea, Macrophomina phaseolina, Rhizoctonia solani, Sclerotinia sclerotiorum, Fusarium oxysporum, Diaporthe phaseolorum var. sojae (Phomopsis sojae), Diaporthe phaseolorum var. caulivora, Sclerotium rolfsii, Cercospora kikuchii, Cercospora sojina, Peronospora manshurica, Colletotrichum dematium (Colletotichum truncatum), Corynespora cassiicola, Septoria glycines, Phyllosticta sojicola, Alternaria alternata, Pseudomonas syringae p.v. glycinea, Xanthomonas campestris p.v. phaseoli, Microsphaera diffusa, Fusarium semitectum, Phialophora gregata, Soybean mosaic virus, Glomerella glycines, Tobacco Ring spot virus, Tobacco Streak virus, Phakopsora pachyrhizi, Pythium aphanidermatum, Pythium ultimum, Pythium debaryanum, Tomato spotted wilt virus, Heterodera glycines Fusarium solani; Canola: Albugo candida, Alternaria brassicae, Leptosphaeria maculans, Rhizoctonia solani, Sclerotinia sclerotiorum, Mycosphaerella brassicicola, Pythium ultimum, Peronospora parasitica, Fusarium roseum, Alternaria alternata; Alfalfa: Clavibacter michiganese subsp. insidiosum, Pythium ultimum, Pythium irregulare, Pythium splendens, Pythium debaryanum, Pythium aphanidermatum, Phytophthora megasperma, Peronospora trifoliorum, Phoma medicaginis var. medicaginis, Cercospora medicaginis, Pseudopeziza medicaginis, Leptotrochila medicaginis, Fusarium oxysporum, Verticillium albo-atrum, Xanthomonas campestris p.v. alfalfae, Aphanomyces euteiches, Stemphylium herbarum, Stemphylium alfalfae, Colletotrichum trifolii, Leptosphaerulina briosiana, Uromyces striatus, Sclerotinia trifoliorum, Stagonospora meliloti, Stemphylium botryosum, Leptotrichila medicaginis; Wheat: Pseudomonas syringae p.v. atrofaciens, Urocystis agropyri, Xanthomonas campestris p.v. translucens, Pseudomonas syringae p.v. syringae, Alternaria alternata, Cladosporium herbarum, Fusarium graminearum, Fusarium avenaceum, Fusarium culmorum, Ustilago tritici, Ascochyta tritici, Cephalosporium gramineum, Collotetrichum graminicola, Erysiphe graminis fsp. tritici, Puccinia graminis fsp. tritici, Puccinia recondita fsp. tritici, Puccinia striiformis, Pyrenophora tritici-repentis, Septoria nodorum, Septoria tritici, Septoria avenae, Pseudocercosporella herpotrichoides, Rhizoctonia solani, Rhizoctonia cerealis, Gaeumannomyces graminis var. tritici, Pythium aphanidermatum, Pythium arrhenomanes, Pythium ultimum, Bipolaris sorokiniana, Barley Yellow Dwarf Virus, Brome Mosaic Virus, Soil Borne Wheat Mosaic Virus, Wheat Streak Mosaic Virus, Wheat Spindle Streak Virus, American Wheat Striate Virus, Claviceps purpurea, Tilletia tritici, Tilletia laevis, Ustilago tritici, Tilletia indica, Rhizoctonia solani, Pythium arrhenomannes, Pythium gramicola, Pythium aphanidermatum, High Plains Virus, European wheat striate virus; Sunflower: Plasmopora halstedii, Sclerotinia sclerotiorum, Aster Yellows, Septoria helianthi, Phomopsis helianthi, Alternaria helianthi, Alternaria zinniae, Botrytis cinerea, Phoma macdonaldii, Macrophomina phaseolina, Erysiphe cichoracearum, Rhizopus oryzae, Rhizopus arrhizus, Rhizopus stolonifer, Puccinia helianthi, Verticillium dahliae, Erwinia carotovorum pv. carotovora, Cephalosporium acremonium, Phytophthora cryptogea, Albugo tragopogonis; Corn: Colletotrichum graminicola, Fusarium moniliforme var. subglutinans, Erwinia stewartii, F. verticillioides, Gibberella zeae (Fusarium graminearum), Stenocarpella maydi (Diplodia maydis), Pythium irregulare, Pythium debaryanum, Pythium graminicola, Pythium splendens, Pythium ultimum, Pythium aphanidermatum, Aspergillus flavus, Bipolaris maydis O, T (Cochliobolus heterostrophus), Helminthosporium carbonum I, II & III (Cochliobolus carbonum), Exserohilum turcicum I, II & III, Helminthosporium pedicellatum, Physoderma maydis, Phyllosticta maydis, Kabatiella maydis, Cercospora sorghi, Ustilago maydis, Puccinia sorghi, Puccinia polysora, Macrophomina phaseolina, Penicillium oxalicum, Nigrospora oryzae, Cladosporium herbarum, Curvularia lunata, Curvularia inaequalis, Curvularia pallescens, Clavibacter michiganense subsp. nebraskense, Trichoderma viride, Maize Dwarf Mosaic Virus A & B, Wheat Streak Mosaic Virus, Maize Chlorotic Dwarf Virus, Claviceps sorghi, Pseudonomas avenae, Erwinia chrysanthemi pv. zea, Erwinia carotovora, Corn stunt spiroplasma, Diplodia macrospora, Sclerophthora macrospora, Peronosclerospora sorghi, Peronosclerospora philippinensis, Peronosclerospora maydis, Peronosclerospora sacchari, Sphacelotheca reiliana, Physopella zeae, Cephalosporium maydis, Cephalosporium acremonium, Maize Chlorotic Mottle Virus, High Plains Virus, Maize Mosaic Virus, Maize Rayado Fino Virus, Maize Streak Virus, Maize Stripe Virus, Maize Rough Dwarf Virus; Sorghum: Exserohilum turcicum, C. sublineolum, Cercospora sorghi, Gloeocercospora sorghi, Ascochyta sorghina, Pseudomonas syringae p.v. syringae, Xanthomonas campestris p.v. holcicola, Pseudomonas andropogonis, Puccinia purpurea, Macrophomina phaseolina, Perconia circinata, Fusarium moniliforme, Alternaria alternata, Bipolaris sorghicola, Helminthosporium sorghicola, Curvularia lunata, Phoma insidiosa, Pseudomonas avenae (Pseudomonas alboprecipitans), Ramulispora sorghi, Ramulispora sorghicola, Phyllachara sacchari, Sporisorium reilianum (Sphacelotheca reiliana), Sphacelotheca cruenta, Sporisorium sorghi, Sugarcane mosaic H, Maize Dwarf Mosaic Virus A & B, Claviceps sorghi, Rhizoctonia solani, Acremonium strictum, Sclerophthona macrospora, Peronosclerospora sorghi, Peronosclerospora philippinensis, Sclerospora graminicola, Fusarium graminearum, Fusarium oxysporum, Pythium arrhenomanes, Pythium graminicola, etc.
Nematodes include parasitic nematodes such as root-knot, cyst, and lesion nematodes, including Heterodera spp., Meloidogyne spp., and Globodera spp.; particularly members of the cyst nematodes, including, but not limited to, Heterodera glycines (soybean cyst nematode); Heterodera schachtii (beet cyst nematode); Heterodera avenae (cereal cyst nematode); and Globodera rostochiensis and Globodera pailida (potato cyst nematodes). Lesion nematodes include Pratylenchus spp.
Various changes in phenotype are of interest including modifying the fatty acid composition in a plant, altering the amino acid content of a plant, altering a plant's pathogen defense mechanism, and the like. These results can be achieved by providing expression of heterologous products or increased expression of endogenous products in plants.
Genes of interest are reflective of the commercial markets and interests of those involved in the development of the crop. Crops and markets of interest change, and as developing nations open up world markets, new crops and technologies will emerge also. In addition, as our understanding of agronomic traits and characteristics such as yield and heterosis increase, the choice of genes for transformation will change accordingly. General categories of genes of interest include, for example, those genes involved in information, such as zinc fingers, those involved in communication, such as kinases, and those involved in housekeeping, such as heat shock proteins. More specific categories of transgenes, for example, include genes encoding important traits for agronomics, insect resistance, disease resistance, herbicide resistance, sterility, grain characteristics, and commercial products. Genes of interest include, generally, those involved in oil, starch, carbohydrate, or nutrient metabolism as well as those. In addition, genes of interest include genes encoding enzymes and other proteins from plants and other sources including prokaryotes and other eukaryotes.
The Bs3 gene of pepper was isolated by from previously identified bacterial artificial chromosome (BAC) clones derived from the pepper (Capsicum annuum) cultivar Early Californian Wonder 30R (ECW-30R) that cover the Bs3 gene (Jordan et al. (2006) Theor. Appl. Genet. 113:895).
Pepper (Capsicum annuum) plants of cultivar Early California Wonder (ECW) and the near-isogenic line ECW-30R containing the resistance gene Bs3 and N. benthamiana plants were grown in the greenhouse under standard conditions (day and night temperatures of 24 and 19° C., respectively), with 16 h of light and 60 to 40% humidity. Pepper cultivar ECW and the near-isogenic line ECW-30R seeds were provided by R. E. Stall (University of Florida, Gainesville). Six-week-old pepper plants were inoculated with Xanthomonas with 5×108 colony forming units/ml with a needle-less syringe. For cycloheximide treatment, leaf tissue was inoculated with a bacterial suspension as above, containing 50 μM cycloheximide.
Complementation with BAC Sub-Clones
BAC clone 128, which spans the Bs3 locus (Jordan et al. (2006) Theor. Appl. Genet. 113:895), was partially digested with HindIII (Fermentas, St. Leon-Rot, Germany). Restriction fragments of ≧10 kb were ligated into the binary-vector pVB61 (Schornack et al. (2004) Plant J. 37:46), which contains no promoter in its T-DNA region, and transformed into A. tumefaciens strain GV3101 (M. Holsters et al. (1980) Plasmid 3:212). Transformants (OD600=0.8) were mixed 1:1 with an A. tumefaciens strain that delivers a T-DNA containing 35S-driven avrBs3. The mixture was injected into the lower side of fully expanded leaves of C. annuum cultivar ECW or N. benthamiana with a blunt syringe. A. tumefaciens strains that delivered the Bs3 gene induced an HR 3-4 days after inoculation.
Proteins with sequence similarity to pepper Bs3 were identified by BLAST searching of databases at the National Center for Biotechnology Information (www.ncbi.nlm.nih.gov/BLAST/) and the SOL Genomics Network (http://www.sgn.cornell.edu/tools/blast/). FMO-like sequences from Arabidopsis were retrieved from TAIR (www.arbidopsis.org). Sequences were aligned with the ClustalW program (http://www.ebi.ac.uk/clustalw/) and the alignments visualized with the boxshade 3.21 program (http://www.ch.embnet.org/software/BOX_form.html). Tree-View 1.5.2 was used for generating a tree based on the ClustalW output.
For complementation-based-identification, fragments of a Bs3 containing BAC (Jordan et al. (2006) Theor. Appl. Genet. 113:895) were cloned into a plant transformation vector and were delivered into Nicotiana benthamiana leaves via Agrobacterium tumefaciens-mediated transient transformation. Two non-identical clones carrying the same coding sequence triggered an HR in N. benthamiana when co-transformed with avrBs3. A genomic DNA fragment containing only the predicted coding sequence and 1 kb of sequence upstream of the ATG mediated AvrBs3 recognition, confirming that this gene is Bs3 (
AvrBs3 mutants lacking the AD domain (AvrBs3ΔAD) or repeat units 11-14 (AvrBs3Δrep16) did not trigger HR in pepper Bs3 plants (Herbers et al. (1992) Nature 356:172; Szurek et al. (2001) Plant J. 26:523) and also failed to trigger HR in N. benthamiana when co-expressed with the cloned Bs3 gene (
The Bs3 gene has three exons and two introns (
Previous analysis showed that the AvrBs3-derivative AvrBs3 Δrep 16 (lacks repeat units 11-14) triggers HR in the pepper cultivar ECW but not in the near-isogenic Bs3-resistant cultivar ECW-30R (Herbers et al. (1992) Nature 356:172). N. benthamiana was transformed with the ECW Bs3 allele (termed Bs3-E) including ˜1 kb of the promoter and showed that it mediated recognition of AvrBs3Δrep16 but not AvrBs3 (
The Bs3 promoter was fused to the Bs3-E coding sequence and vice versa and co-transformed N. benthamiana with these chimeras in combination with avrBs3, avrBs3Δrep16 or the corresponding AD mutant derivatives.
Chimerical gene constructs were generated by splicing using overlap extension (SOE) PCR (Horton et al. (1989) Gene 77:61). Bs3 and Bs3-E promoters were amplified from genomic DNA of ECW and ECW-30R pepper cultivars, respectively, with the Phusion-polymerase and A1-fwd-PR (CTACGGAATAGCAGCATTAAGGCACATCAG; SEQ ID NO: 18) and B5-rev-PR (CATACGGAACACTGTATTGCTTAAGG; SEQ ID NO: 19) primers. The coding regions were amplified with final-entry-01-fwd (ATGATGAATCAGAATTGCTTTAATTCTTGTTC; SEQ ID NO: 20) and final-entry-02-rev (CATTTGTTCTTTCCAAATTTTGGCAATATC; SEQ ID NO: 21) primers. PCR-products of the coding and promoter region were mixed in a 1:1 ratio and PCR amplified using A1-fwd-PR and final-entry-02-rev primers. The PCR-product was cloned into pENTR-D and, after sequencing, recombined into the T-DNA vector pGWB1.
The Bs3 promoter fused to the Bs3-E coding sequence mediated exclusively AvrBs3 recognition while the reciprocal chimera (Bs3-E promoter fused to the Bs3 coding sequence) mediated exclusively recognition of AvrBs3Δrep16 (
The abaxial leaf surface of ECW and ECW-30R pepper plants was inoculated with Xcv strain 85-10 (OD600=0.4) with a blunt syringe. Inoculations were carried out with isogenic Xcv strains expressing avrBs3 (pDS300F) (Van den Ackerveken et al. (1996) Cell 87:1307), avrBs3ΔAD (pDSF341) (Szurek et al. (2001) Plant J. 26:523), avrBs4 (pDSF200) (Schornack et al. (2004) Plant J. 37:46), avrBs3Δrep16 (pDSF316) (Herbers et al. (1992) Nature 356:172) or avrBs3Δrep16ΔAD (pDSF317). Four leaf discs (5-mm diameter) were harvested 24 hours after inoculation and were used for each RNA-extraction using the Qiagen RNeasy Plant Miniprep kit (Qiagen, Hilden, Germany). RNA concentrations were determined with a ND-1000 spectrophotometer (Nanoprop Technologies, Rockland, Del., USA) and adjusted prior to cDNA synthesis. cDNA was synthesized by reverse transcription using an oligo dT-primer and the Revert Aid First Strand Synthesis Kit (Fermentas, St. Leon-Rot, Germany). For RT-PCR of Bs3 the Cand-7-01-fwd (ATGAATCAGAATTGCTTTAATTCTTGTTCA; SEQ ID NO: 22) and Cand-7-01-rev (TGATTCTTGTGCTACATTTGTTCTTTCC; SEQ ID NO: 23) primers were used. To amplify EF1α (used for RT-PCR normalization) primers RS-EFrt-F1 (AGTCAACTACCACTGGTCAC; SEQ ID NO: 24) and RS-EFrt-R1 (GTGCAGTAGTACTTAGTGGTC; SEQ ID NO: 25) were used. The 5′ and 3′ ends of the Bs3 and Bs3-E cDNAs were isolated by rapid amplification of cDNA ends (RACE) using the SMART RACE Kit (Clontech, Heidelberg, Germany).
Semi-quantitative RT-PCR revealed strongly increased Bs3 transcript levels in pepper ECW-30R Bs3 plants upon infection with avrBs3-expressing, but not avrBs3Δrep16- or avrBs4-expressing Xcv strains (
The pepper cultivar ECW-123R containing the R genes Bs1, Bs2 and Bs3 was infected with xanthomonads delivering either the structurally unrelated AvrBs1, AvrBs2 or AvrBs3 protein or none of these Avr proteins. RT-PCR showed that the Bs3-derived transcripts were detectable only upon infection with avrBs3-expressing Xcv strains (
For DNA binding studies, GST fusion proteins were purified from E. coli BL21 with Glutathione Sepharose 4B (GE Healthcare Bio-Sciences AB, Uppsala) and the protein concentration was determined by Bradford protein assay (BioRad, Hercules, Calif., U.S.A.). Complementary pairs of nonlabeled or 5′-biotin-labeled oligonucleotides were annealed. EMSA was performed with the Light Shift® Chemiluminescent EMSA Kit (Pierce, Rockford) according to the manufacturer's protocol. The following parameters were used: Binding reactions contained 12 mM Tris-HCl (pH 7.5), 60 mM KCl, 1 mM DTT, 2.5% Glycerol, 5 mM MgCl2, 50 ng/μl poly(dI·dC), 0.05% NP-40, 0.2 mM EDTA, 50 fmol biotin-labeled DNA, 0-10 pmol unlabeled DNA, 60-600 fmol GST fusion protein. The binding reactions were kept on ice for 10 min before biotin-labeled DNA was added. Gel electrophoresis was performed on a 6% native polyacrylamide gel. After blotting to a positively charged nylon membrane (Roche Diagnostics, Mannheim) the DNA was linked by baking at 100° C. for 1 h.
Electrophoretic mobility shift assays (EMSAs) with GST-AvrBs3 fusion protein and biotin-labeled Bs3 and Bs3-E promoter fragments (
For ChIP, 3 g pepper ECW or ECW-30R leaf material was harvested 12 hours post inoculation (hpi) with X. campestris pv. vesicatoria strains 82-8 and 82-8ΔhrcV, respectively. ChIP was performed as described (Offermann et al. (2006) Plant Physiol. 141:1078) with the following modifications: All buffers were supplemented with DTT instead of β-mercaptoethanol. 1× complete (Roche) was used as proteinase inhibitor. The chromatin was sonicated 6×20 sec with a Branson sonifier G250 (output control 3) and diluted 1:8.5 with ChIP dilution buffer. 100 μl pre-cleared chromatin solution was saved as input control, the rest was subjected to immunoprecipitation with 15 μl of affinity-purified and depleted AvrBs3-specific antibody Sta7 (Bonas et al. (1993) Mol. Gen. Genet. 238:261). The recovered DNA was analyzed by semi-quantitative PCR with input DNA as loading control. Different PCR cycle numbers were tested for both input and co-precipitated DNA.
Chromatin immunoprecipitation assays were performed by infiltrating pepper ECW-30R (Bs3) and ECW (Bs3-E) leaves either with avrBs3-expressing Xcv wild-type strains or with an isogenic hrcV mutant strain. HrcV is a conserved protein of the core T3S system with mutants incapable of delivering T3S effector proteins (Rossier et al. (1999) Proc. Natl. Acad. Sci. USA 96:9368). After immunoprecipitation with an AvrBs3 antibody (Knoop et al. (1991) J. Bacteriol. 173:7142), enrichment of the Bs3 but not the Bs3-E promoter region was detected by semi-quantitative PCR (
Isolation of the pepper Bs3 gene uncovered a mechanistically novel type of recognition mechanism and a structurally novel type of R protein that shares homology to FMOs. Recently, FMO1, an Arabidopsis protein that is sequence-related to Bs3 (see
The results disclosed herein demonstrate that the bacterial effector protein AvrBs3 binds to and activates the promoter of the matching pepper R gene Bs3. Analysis of host genes that are unregulated by AvrBs3 (“upa” genes) in a compatible Xcv-pepper interaction (Marois et al. (2002) Mol Plant-Microbe Interact. 15:637-646; Kay et al. (2007) Science submitted) led to the identification of the upa-box (TATATAAACCN2-3CC; SEQ ID NO: 17), a conserved DNA element that was shown to be bound by AvrBs3 and that is also present in the Bs3 promoter (
It is likely that not only AvrBs3 but also other AvrBs3 homologs bind to and activate promoters of matching R genes. The recently isolated rice R gene Xa27, which mediates recognition of the AvrBs3-like AvrXa27 protein from Xanthomonas oryzae pv. oryzae (Gu et al. (2005) Nature 435:1122) is transcriptionally induced by AvrXa27 and thus it is tempting to speculate that the Xa27 promoter is a direct target of AvrXa27. However, whether AvrXa27 acts directly at the Xa27 promoter remains to be clarified.
The article “a” and “an” are used herein to refer to one or more than one (i.e., to at least one) of the grammatical object of the article. By way of example, “an element” means one or more element.
Throughout the specification the word “comprising,” or variations such as “comprises” or “comprising,” will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.
All publications and patent applications mentioned in the specification are indicative of the level of those skilled in the art to which this invention pertains. All publications and patent applications are herein incorporated by reference to the same extent as if each individual publication or patent application was specifically and individually indicated to be incorporated by reference.
Although the foregoing invention has been described in some detail by way of illustration and example for purposes of clarity of understanding, it will be obvious that certain changes and modifications may be practiced within the scope of the appended claims.
This application claims the benefit of U.S. Provisional Application No. 60/976,017, filed Sep. 28, 2007, which is hereby incorporated herein in its entirety by reference.
| Number | Date | Country | |
|---|---|---|---|
| 60976017 | Sep 2007 | US |
