FUNCTIONAL R-GENE FROM SOLANUM BULBOCASTANUM

The invention relates to a resistance gene isolated from S. bulbocastanum. Moreover, the invention relates to the use of said resistance gene, for example to clone functional homologues, and the use of said resistance gene(s) in a method to increase or confer at least partial resistance to an oomycte infection in a plant. More in specific the invention provides a resistance gene that is capable of increasing or conferring at least partial resistance to Phytophthora (for example Phytophthora infestans).

Late blight, caused by the oomycete Phytophthora infestans,is one of the most serious diseases in worldwide potato production. It was responsible for the Irish potato famine of the mid-19th century, resulting in the death of one million people. Although a lot of effort has been invested in controlling the pathogen, chemical control of P. infestans is still the main crop management strategy, but environmental safety is becoming more important and the pathogen is sometimes able to evolve chemical resistance. Therefore, introduction of resistance into modern potato varieties is the most durable strategy to control the disease.

In the last century, Solanum demissum, which is a hexaploid Mexican species, was extensively used in breeding for late-blight resistance in potato. Initially, a series of 11 R genes derived from S. demissum was described. Of these, R1, R2, R3a/b, R6, and R7 have been localized on the genetic maps of potato. However, these R genes confer race-specific resistance and those that were introgressed into potato varieties, mainly R1, R2, R3, R4, and R10, were quickly overcome by the pathogen. Hence, new sources for resistance are required, and currently, several other wild Solanum species have been reported as being potential sources of resistance, many of which have currently been genetically characterized (Table 1).

S. bulbocastanum, a self-incompatible diploid species from Mexico, is thought to be a source for late-blight resistance. Introduction of S. bulbocastanum derived resistance has been achieved through interspecific bridge crosses between S. bulbocastanum, S. acaule, S. phureja, and S. tuberosum (Hermsen and Ramanna, Euphytica 22: 457-466, 1973), resulting in so-called ABPT material that is widely used for potato late-blight breeding. Additionally, Helgeson et al (Theor. Appl. Genet. 96:738-742, 1998) generated somatic hybrids between S. bulbocastanum and cultivated potato. The somatic hybrids led to fertile plants that retained resistance and could be used for breeding. Molecular cloning of the genes responsible for resistance and subsequent introduction of the genes into potato varieties is a third method that circumvents many of the problems encountered in the previous two strategies.

To date, two R genes from S. bulbocastanum have been cloned, the allelic genes RB and Rpi-blb1 on chromosome 8 (Song et al. Proc. Natl. Acad. Sci 100: 9128-9133, 2003; van der Vossen et al. Plant Journal 36: 867-882, 2003) and Rpi-blb2 on chromosome 6 (van der Vossen et al. Plant Journal 44: 208-222, 2005). As shown in Table 5, Rpi-blb1 as well as Rpi-blb2 provide protection against a diverse set of Phytophthora infestans isolates. Until the present invention no Phytophthora isolates were described that could colonize plants harboring Rpi-blb1, hence the specification ‘broad spectrum resistance gene’ was used to describe the protection conferred by this gene. However, as disclosed in Table 5, Phytophthora isolate 99189 is able to grow on Rpi-blb1 plants and thus to ‘break’ the resistance, suggesting race specificity.

Although the initial results obtained with RB and Rpi-blb1 and Rpi-blb2 are promising, there is a further need for additional R-genes. The present invention describes the cloning of a third late blight R gene from S. bulbocastanum. The Rpi-blb3 gene was mapped to an R gene hotspot on chromosome 4 in an intraspecific S. bulbocastanum mapping population. Markers highly linked to Rpi-blb3 were used to generate a physical map of the R locus. Two R gene candidates (RGC) present on one of two BAC clones that encompassed the Rpi-blb3 locus were targeted for complementation analysis, one of which turned out to be the functional Rpi-blb3 gene. Surprisingly, Rpi-blb3 shares the highest amino acid sequence identity (34.9%) to RPP13 from Arabidopsis thaliana and very little homology to any R gene previously identified within the Solanaceae.

As shown in Table 5, the 3 R genes cloned from S. bulbocastanum give differential reactions to the isolates 99177 and 99189 and hence it is concluded that these 3 R-genes are functionally different. Moreover, due to the large sequence differences it is likely that the 3 R-genes recognise different effectors from Phytophthora. This is confirmed by the fact that Rpi-blb1 recognises ipiO whereas the two other R-gene products do not recognise this Phytophthora effector.

In a first embodiment, the invention provides an isolated or recombinant nucleic acid sequence comprising a nucleic acid sequence encoding the amino acid sequence Rpi-blb3 of FIG. 6 or a functional fragment or a functional homologue thereof, i.e. a functional fragment or a functional homologue of the amino sequence as shown in FIG. 6.

The term “nucleic acid” means a single or double stranded DNA or RNA molecule.

Also included are the complementary sequences of the herein described nucleotide sequences.

The term “functional fragment thereof” is typically used to refer to a fragment of the Rpi-blb3 protein that is capable of providing at least partial resistance or increasing resistance in a plant of the Solanaceae family against an oomycte infection. Such a fragment is a truncated version of the Rpi-blb3 protein as presented in FIG. 6. A truncated version/fragment of the Rpi-blb3 protein is a fragment that is smaller than 847 amino acids and preferably comprises the larger part of the LRR domain (i.e. the larger part of the leucine-rich repeat domain which stretches from about amino acid 512 to amino acid 827 of Rpi-blb3) and/or the N-terminal parts of the Rpi-blb3 protein.

The term “functional homologue” is typically used to refer to a variant of the herein described Rpi-blb3 protein, which variant is capable of providing at least partial resistance or increasing resistance in a plant of the Solanaceae family against an oomycte infection. Included are artificial changes or amino acid residue substitutions that at least partly maintain the effect of the Rpi-blb3 protein. For example, certain amino acid residues can conventionally be replaced by others of comparable nature, e.g. a basic residue by another basic residue, an acidic residue by another acidic residue, a hydrophobic residue by another hydrophobic residue, and so on. Examples of hydrophobic amino acids are valine, leucine and isoleucine. Phenylalanine, tyrosine and tryptophan are examples of amino acids with an aromatic side chain and cysteine as well as methonine are example of amino acids with sulphur-containing side chains. Serine and threonine contain aliphatic hydroxyl groups and are considered to be hydrophilic. Aspartic acid and glutamic acid are examples of amino acids with an acidic side chain. In short, the term “functional homologue thereof” includes variants of the Rpi-blb3 protein in which a portion of the amino acids have been replaced conventionally and which at least partly maintain the effect of the Rpi-blb3 protein (i.e. at least partly providing or increasing resistance in a plant of the Solanaceae family against an oomycte infection). Also included in the term “functional homologue thereof” are homologous sequences. Preferably, such a homologue has at least 40% identity on the amino acid level. More preferably, the amino acid homology percentage is at least 86 or 90%. Even more preferred are amino acid homology percentages of 91, 92, 93, 94 or 95%. Most preferred are amino acid homology percentages of 96, 97, 98 or 99%.

A homologous nucleic acid sequence is a nucleic acid sequence that encodes for a homologous protein as described above. Homologous proteins and their respective nucleotide sequences are, for example, the genes denominated as Rpi-abpt, R2-like and R2, see FIG. 6 (amino acid sequence) and FIGS. 9-11 (nucleotide sequence).

Homology percentages can for example be determined by using computer programs such as BLAST, ClustalW or ClustalX.

Many nucleic acid sequences code for a protein that is 100% identical to the Rpi-blb3 protein as presented in FIG. 6. This is because the third nucleotide in a nucleotide triplet may vary without changing the corresponding amino acid (wobble position in the nucleotide triplets). Thus, without having an effect on the amino acid sequence of a protein the nucleotide sequence coding for this protein can be varied. However, in a preferred embodiment, the invention provides an isolated or recombinant nucleic acid sequence as depicted in FIG. 8. The Rpi-blb3 coding region of 2544 by is highlighted in lower case (2944-5487). The upstream 2732 nt (211-2942) and the downstream 882 nt (5488-6370) harbour regulatory sequences. In a preferred embodiment, the invention provides an isolated or recombinant nucleic acid that represents the coding sequence (CDS) of the Rpi-blb3 protein, i.e. nucleotides 2944-5487 of FIG. 8 or a functional part or a functional homologue thereof.

Fragments as well as homologues of the herein described Rpi-blb3 gene and protein can for example be tested for their functionality by using Agrobacterium tumefaciens transient assays (ATTA) and/or by using a detached leaf assay.

The experimental part for example describes a functional screen for testing candidate genes using Agrobacterium tumefaciens transient assays (ATTA) whereby 4 week old wildtype Nicotiana benthamiana plants are infiltrated with an Agrobacterium strain containing the candidate Rpi-blb3 homologue. The infiltrated leaves are subsequently challenged one day after infiltration with a P. infestans strain that is virulent on N. benthamina, for example IPO-C or 90128, in detached leaf assays. This system is equally suitable for testing candidate homologous fragments of Rpi-blb3.

The ATTA assays make use of transient expression. Transient gene expression is a fast, flexible and reproducible approach to high-level expression of useful proteins. In plants, recombinant strains of Agrobacterium tumefaciens can be used for transient expression of genes that have been inserted into the T-DNA region of the bacterial Ti plasmid. A bacterial culture is infiltrated into leaves, and upon T-DNA transfer, there is ectopic expression of the gene of interest in the plant cells. However, the utility of the system is limited because the ectopic protein expression ceases after 2-3 days. It is shown that post-transcriptional gene silencing (PTGS) is a major cause for this lack of efficiency. A system based on co-expression of a viral-encoded suppressor of gene silencing, the p19 protein of tomato bushy stunt virus (TBSV), prevents the onset of PTGS in the infiltrated tissues and allows high level of transient expression. Expression of a range of proteins was enhanced 50-fold or more in the presence of p19 so that protein purification could be achieved from as little as 100 mg of infiltrated leaf material. Although it is clear that the use of p19 has advantages, an ATTA without p19 can also be used to test the functionality of candidate fragments and homologues.

Alternatively, each candidate gene (for example being a fragment or homologue) construct is targeted for transformation to a susceptible potato cultivar, for example Desiree. Primary transformants are challenged in detached leaf assays using for example isolates IPO-0, IPO-C or 90128. Transformants that are resistant to these isolates harbour for example functional fragments or homologues of Rpi-blb3.

In yet another embodiment, the invention provides a vector comprising a nucleic acid as provided herein, i.e. a nucleic acid capable of providing at least partial resistance or increasing resistance in a plant of the Solanaceae family against an oomycete infection. More particularly, the invention provides a vector comprising an isolated or recombinant nucleic acid sequence comprising a nucleic acid sequence encoding the amino acid sequence Rpi-blb3 of FIG. 6 or a functional fragment or a functional homologue thereof. The invention also provides a vector comprising a nucleic acid sequence as depicted in FIG. 8, preferably the coding sequence of FIG. 8, i.e. nucleotide 2944-5487.

Examples of a suitable vector are pBeloBACII, pBINPLUS, pKGW-MG or any commercially available cloning vector.

As will be outlined below there are multiple ways in which a nucleic acid of the invention can be transferred to a plant. One suitable means of transfer is mediated by Agrobacterium in which the nucleic acid to be transferred is part of a binary vector and hence it is preferred that the above described vector is a binary vector.

The invention further provides a host cell comprising a nucleic acid as described herein or a vector as described herein. Examples of a preferred host cell are an E. coli cell suitable for BAC clones (e.g. DH10B) or an Agrobacterium (host) cell. In an another embodiment, said host cell comprises a plant cell. A preferred plant cell is a cell derived from a member of the Solanaceae family and even more preferred said plant cell comprises a cell from Solanum tuberosum or Solanum lycopersicum, formerly known as Lycopersicon esculentum. From such a cell, a transgenic or genetically modified plant (for example a potato or tomato plant) can be obtained by methods known by the skilled person (for example regeneration protocols).

The invention further provides a leaf, tuber, fruit or seed or part or progeny of a genetically modified plant as described herein.

In yet another embodiment, the invention provides a protein encoded by the herein described isolated or recombinant nucleic acid or a functional fragment or a functional homologue thereof. In a preferred embodiment, the invention provides a protein encoded by a nucleic acid sequence as depicted in FIG. 8, preferably a protein encoded by nucleotides 2944-5487. In yet another preferred embodiment, the invention provides a protein comprising the amino acid sequence of FIG. 6 or a functional fragment or a functional homologue thereof.

The herein described Rpi-blb3 protein comprises 847 amino acids and the LRR domains of Rpi-blb3 consist of 14 imperfect repeats (FIG. 6). Interestingly Rpi-blb3 shares the highest homology with the RPP13 protein from Arabidopsis thaliana (Table 3) (Bittner-Eddy et al., Plant Journal 21: 177-188, 2000). The different domains of Rpi-blb3 share varying degrees of homology with corresponding domains of RPP13 (Table 3). The NBS domain is most conserved (48.2% aa identity), followed by the CC domain (34.4% aa identity). The LRR domain is least conserved (21.5% aa identity) (Table 3). The RPP13 gene in A. thaliana controls resistance to the oomycete pathogen, Hyaloperenospora parasitica.

As already described, a functional fragment or a functional homologue thereof of Rpi-blb3 is a fragment or homologue that is capable of providing at least partial resistance or increasing resistance in a plant of the Solanaceae family against an oomycte infection.

Means to test the functionality of a functional fragment or a functional homologue of Rpi-blb3 have been provided above. With these assays the inventors, e.g. through allel mining, found additional functional homologues. These homologues are denominated as Rpi-abpt, R2-like and R2 (see FIG. 6). The functionality test reported in Table 5 shows that transgenes for these genes are resistant to P. infestans. However, it also appears that slight differences in the spectrum of resistance are discernable between these homologues, especially with respect to P. infestans isolates 99190, 99183 and 99189.

Based on the herein described nucleic acid sequences, the invention also provides probes and primers (i.e. oligonucleotide sequences complementary to one of the (complementary) DNA strands as described herein). Probes are for example useful in Southern or Northern analysis and primers are for example useful in PCR analysis. Primers based on the herein described nucleic acid sequences are very useful to assist plant breeders (active in the field of classical breeding and/or breeding by genetic modification of the nucleic acid content of a plant (preferably said plant is a Solanum tuberosum or Solanum lycopersicum, formerly known as Lycopersicon esculentum), in selecting a plant that is capable of expressing Rpi-blb3.

Hence, in a further embodiment, the invention provides a binding molecule capable of binding to a nucleic acid as described herein or its complementary nucleic acid. In a preferred embodiment, said binding molecule is a primer or a probe. As mentioned, such a binding molecule is very useful for plant breeders and hence the invention further provides a method for selecting a plant or plant material or progeny thereof for its susceptibility or resistance to an oomycete infection said method comprising the steps of testing at least part of said plant or plant material or progeny thereof for the presence or absence of a nucleic acid as described herein, e.g. a nucleic acid encoding Rpi-blb3. In a preferred embodiment, said method further comprises providing a binding molecule as described herein, such as a primer or a probe. In yet another preferred embodiment, the nucleic acid of a to be tested plant is isolated from said plant and the obtained isolated nucleic acid is brought in contact with one or multiple (preferably different) binding molecule(s). One can for example use a PCR analysis to test plants for the presence of absence of Rpi-blb3 in the plant genome.

The herein described Rpi-blb3 protein can also be used to elicit antibodies by means known to the skilled person. The invention thus also provides an antibody that (specifically) binds to the protein encoded by the herein described isolated or recombinant nucleic acid (for example the nucleic acid sequence of FIG. 8 and especially the nucleotides 2944-5487) or an antibody that (specifically) binds to a protein as depicted in FIG. 6 or a functional fragment or a functional homologue thereof. Such an antibody is for example useful in protein analysis methods such as Western blotting or ELISA.

Based on the herein provided nucleic acid sequences, the invention also provides the means to introduce or increase resistance against an oomycete infection in a plant. The invention therefore also provides a method for providing at least partial resistance or increasing resistance in a plant against an oomycete infection comprising providing a plant or a part thereof with:

Such a method for providing at least partial resistance or increasing resistance in a plant against an oomycete infection involves the transfer of DNA into a plant, i.e., involves a method for transforming a plant cell comprising providing said plant cell with a nucleic acid as described herein or a vector as described herein or a host cell as described herein.

There are multiple ways in which a recombinant nucleic acid can be transferred to a plant cell, for example Agrobacterium mediated transformation. However, besides by Agrobacterium infection, there are other means to effectively deliver of DNA to recipient plant cells when one wishes to practice the invention. Suitable methods for delivering DNA to plant cells are believed to include virtually any method by which DNA can be introduced into a cell, such as by direct delivery of DNA such as by PEG-mediated transformation of protoplasts, by desiccation/inhibition-mediated DNA uptake (Potrykus et al., Mol. Gen. Genet., 199:183-188, 1985), by electroporation (U.S. Pat. No. 5,384,253), by agitation with silicon carbide fibers (Kaeppler et al., 1990; U.S. Pat. No. 5,302,523; and U.S. Pat. No. 5,464,765), and by acceleration of DNA coated particles (U.S. Pat. No. 5,550,318; U.S. Pat. No. 5,538,877; and U.S. Pat. No. 5,538,880). Through the application of techniques such as these, cells from virtually any plant species may be stably transformed, and these cells developed into transgenic plants.

In case Agrobacterium mediated transfer is used, it is preferred to use a substantially virulent Agrobacterium such as A. tumefaciens, as exemplified by strain A281 or a strain derived thereof or another virulent strain available in the art. These Agrobacterium strains carry a DNA region originating from the virulence region of the Ti plasmid pTiBo542 containing the virB, virC and virG genes. The virulence (vir) gene products of A. tumefaciens coordinate the processing of the T-DNA and its transfer into plant cells. Vir gene expression is controlled by virA and virG, whereby virA upon perception of an inducing signal activates virG by phosphorylation. VirG, in turn, induces the expression of virB,C,D,E. These genes code for proteins involved in the transfer of DNA. The enhanced virulence of pTiBo542 is thought to be caused by a hypervirulent virG gene on this Ti plasmid (Chen et al. Mol. Gen. Genet 230; 302-309, 1991).

After transfer of a nucleic acid into a plant or plant cell, it must be determined which plants or plant cells have been provided with said nucleic acid. This is for example accomplished by using a selectable marker or a reporter gene. Among the selective markers or selection genes that are most widely used in plant transformation are the bacterial neomycin phosphotransferase genes (nptI, nptII and nptIII genes) conferring resistance to the selective agent kanamycin, suggested in EP131623 and the bacterial aphIV gene suggested in EP186425 conferring resistance to hygromycin. EP 275957 discloses the use of an acetyl transferase gene from Streptomyces viridochromogenes that confers resistance to the herbicide phosphinotricin. Plant genes conferring relative resistance to the herbicide glyphosate are suggested in EP218571. The resistance is based on the expression of a gene encoding 5-enolshikimate-3-phosphate synthase (EPSPS) that is relatively tolerant to N-phosphomethylglycine. Certain amino acids such as lysine, threonine, or the lysine derivative amino ethyl cysteine (AEC) and tryptophan analogs like 5-methyl tryptophan can also be used as selective agents due to their ability to inhibit cell growth when applied at high concentration. In this selection system expression of the selectable marker gene results in overproduction of amino acids by transgenic cells which permits the transgenic to grow under selection. Suitable examples of reporter genes are beta-glucuronidase (GUS), beta-galactosidase, luciferase and green fluorescent protein (GFP).

In a preferred embodiment, the invention provides a method for providing at least partial resistance or increasing resistance in a plant against an oomycete infection comprising providing a plant or a part thereof with:

The invention also provides a plant that is obtainable by using a method for providing at least partial resistance or increasing resistance in a plant against an oomycete infection as described above. A preferred plant is a plant from the Solanaceae family and even more preferred said plant is a Solanum tuberosum or a Solanum lycopersicum, formerly known as Lycopersicon esculentum. The invention thus also provides a plant that has been provided with a nucleic acid encoding a Rpi-blb3 protein or a functional fragment or a functional homologue thereof. Whether a plant has been provided with a nucleic acid as described herein is for example determined by using a probe or primer that has been designed based on the herein described nucleic acid sequence. One can also use an antibody that (specifically) binds to encoded Rpi-blb3 protein.

The invention further provides a leaf, tuber, fruit or seed or part or progeny of a genetically modified plant comprising a nucleic acid encoding the Rpi-blb3 amino acid sequence of FIG. 6 or a functional fragment or a functional homologue thereof.

In a preferred embodiment, the herein described nucleic acid is transferred to a potato variety other than Solanum bulbocastanum, the herein described nucleic acid is preferably transferred to a non-bulbocastanum background, preferably to a commercial interesting variety such as Bintje, Desiree or Premiere, Spunta, Nicola, Favorit, Russet Burbank, Aveka or Lady Rosetta.

In yet another preferred embodiment, the herein described nucleic acid is foreign to the host cell. The term “foreign” is herein used to describe the situation in which the herein described nucleic acid is heterologous with respect to the host cell (i.e. derived from a cell or organism with a different genomic background) or the herein described nucleic acid is homologous with respect to the used host cell but located in a different genomic environment than the naturally occurring counterpart of said nucleic acid (for example not on the natural locus or located between different genes).

In yet another embodiment, the invention provides a method for providing at least partial resistance or increasing resistance in a plant against an oomycete infection comprising providing a plant or a part thereof with:

an isolated or recombinant nucleic acid sequence comprising a nucleic acid sequence encoding the Rpi-blb3 amino acid sequence of FIG. 6 or a functional fragment or a functional homologue thereof, or

an isolated or recombinant nucleic acid sequence as depicted in FIG. 8, or

a vector comprising the herein described nucleic acid sequences, or

a host cell as described herein,

wherein said plant before being provided with a nucleic acid encoding Rpi-blb3 or a functional part or a functional homologue thereof is at least partly susceptible to an oomycete infection (for example P. infestans). The fact that a plant is partly susceptible/partly resistant to an oomycete infection can be the result of genes naturally present in said plant, but it may also be the result of already introduced (other) resistance genes.

The invention further provides use of an isolated or recombinant nucleic acid sequence comprising a nucleic acid sequence encoding the Rpi-blb3 amino acid sequence of FIG. 6 or a functional fragment or a functional homologue thereof or use of an isolated or recombinant nucleic acid sequence as depicted in FIG. 8 or use of a vector comprising any of said nucleic acid sequences or use of a host cell comprising any of said nucleic acid sequences or said vector for providing a plant with at least partial resistance against an oomycete infection. In a preferred embodiment, said oomycte comprises Phytophthora and even more preferably Phytophthora infestans. In yet another preferred embodiment said plant comprises Solanum tuberosum or Solanum lycopersicum, formerly known as Lycopersicon esculentum.

In yet another embodiment, the invention provides a method for producing Rpi-blb3 protein or a functional fragment or a functional homologue thereof comprising

functionally linking a nucleic acid as described herein to a regulatory sequence and allowing said nucleic acid to be expressed in a host cell. Examples of a regulatory sequence are a promoter and/or terminator sequence.

The invention further provides the promoter and/or terminator sequences of Rpi-blb3 (see FIG. 8). FIG. 8 shows the nucleotide sequence of clone Blb25-B2 (8461 bp) containing the Rpi-blb3 gene and regulatory sequences. The Rpi-blb3 coding region of 2544 by is highlighted in lower case (2944-5487). The upstream 2732 nt (211-2942) and the downstream 882 nt (5488-6370) harbour the regulatory sequences that ensure correct expression of the gene. The skilled person is very well capable of cloning (part of) said regulatory sequences and testing their efficiency in transcription.

The invention will be explained in more detail in the following, non-limiting examples.

Experimental Part
Results

Here we describe the cloning and functional characterization of Rpi-blb3, Rpi-abpt, R2-like and R2 from the major late blight resistance locus on chromosome 4 of potato (Park et al 2005a, 2005b, 2005c; Li et al. 1998)

Cloning of Rpi-blb3 and Rpi-abpt

In order to clone Rpi-blb3 and Rpi-abpt, two BAC libraries were constructed using DNA derived from the resistant clones Blb99-256-3 and 707TG11-1, respectively. Approximately 74000 clones with an average insert size of 85 kb, corresponding to 8 genome equivalents, were obtained for each library. These libraries were screened initially with SCAR marker Th21 (Table 2), which cosegregated with resistance in mapping populations of 1396 and 1383 F1 progeny plants, respectively (Park et al. 2005). In this way BAC clones Blb22 and TG9 were identified, respectively (FIG. 1). By sequencing the ends of these two BACs, new markers (Table 2) were developed which were used to define the genetic intervals of the R loci more precisely and to re-screen the BAC libraries to identify clones that overlapped with the initial BAC clones. In this way the Rpi-blb3 locus was delimited to a 0.3 cM (Blb22S-Blb25T; 4/1396 recombinants) interval that is physically spanned by the two partially overlapping BAC clones Blb22 and Blb25 (FIG. 1A). In case of the Rpi-abpt locus, the partially overlapping BAC clones TG9 and TG77 were identified. One end of the contig cosegregated with resistance (TG77S) while the other mapped 0.1 cM proximal to Rpi-abpt (TG9S) (FIG. 1B).

To gain insight into the molecular structure of the R loci under study, BAC clones Blb22 and TG9 were sequenced to 6× coverage. This revealed that clone Blb22 did not contain any R gene homologues (RGH) whereas clone TG9 contained two RGH, which shared significant homology to RGHs present in the sequenced tomato BAC clone AF411807L (van der Hoeven et al. 2002). BAC clones Blb25 and TG77 were subsequently screened for the presence of RGH specific sequences through PCR analysis using the primers 4-PLOOP-F and 4-GLPL-R (Table 2) which were designed by aligning the RGH sequences of clone AF411807L with those present on BAC clone TG9. Southern analysis of BAC clones Blb22, Blb25, TG9 and TG77 using an RGH specific PCR fragment amplified from BAC clone Blb25 as a probe, identified a minimum of two RGHs on BAC Blb25 and TG9 and one RGH on TG77 (FIG. 1).

Libraries harboring random overlapping binary subclones of 8-10 kb were therefore generated from BAC clones Blb25 and TG9. A total of 1152 clones per library were screened for the presence of RGHs using primers GLO2-F and —R (Table 2). Based on restriction analyses of the PCR fragments, RGH positive subclones were divided into separate classes, Blb3GH-A and Blb3GH-B for Rpi-blb3, AbptGH-A and AbptGH-B for Rpi-abpt. After determining the relative positions of the RGHs within the 8-13 kb subclones, candidates from each class were targeted for transformation to the susceptible potato cultivar Desiree. Transformation experiments carried out with subclones Blb25-A3, Blb25-B2, TG9-A1 and TG9-B2 harboring candidates Blb3GH-A, Blb3GH-B, AbptGH-A and AbptGH-B, respectively, resulted in numerous primary transformants. Detached leaf assays using isolates IPO-0 and 90128 revealed that all of the plants transformed with Blb25-A3, TG9-A1 and TG9-B2 were susceptible to both isolates but that the majority (7/8) of the tested transgenic plants harboring Blb25-B2 reacted to both isolates with a hypersensitive response (HR) (FIG. 2). In view of the differential response between the primary transformants harboring Blb3GH-A and Blb3GH-B, we designated Blb3GH-B as the Rpi-blb3 gene.

In order to identify additional candidate genes for Rpi-abpt, the Rpi-abpt specific BAC library was screened with TG77S, leading to the identification of the TG77 overlapping BAC clone TG92 (FIG. 1B). Screening of this BAC clone with different sets of primers designed to amplify AbptGH-A, AbptGH-B, Blb3GH-A or Rpi-blb3, resulted in the identification of a third Rpi-abpt candidate gene, AbptGH-C (FIG. 1B), which, when converted into a specific marker (AbptGH-C; Table 2 and FIG. 1B), also cosegregated with resistance. Southern blot analysis using the AbptGH-C amplicon as a probe revealed that clone TG92 contained only a single RGH. Primers designed on the start and stop codon of Rpi-blb3 (B1b3-start and Blb3-end, Table 2) were subsequently used to amplify a full-length AbptGH-C amplicon from clone TG92, which was cloned into the Gateway® entry vector pDONR221. Using Multisite Gateway® technology, the AbptGH-C amplicon was subsequently cloned into the binary pKGW-MG destination vector between Rpi-blb3 derived promoter and terminator sequences of 2723 nt and 883 nt, which were cloned into pDONR™ P4-P1R and pDONR™ P2R-P3 (FIG. 3).

Complementation analysis was carried out in Nicotiana benthamiana using the Agrobacterium tumefaciens transient assay (ATTA) whereby 4-week old wildtype N. benthamiana plants were infiltrated with the Agrobacterium strain COR308 containing pKGW-AbptGH-C. The binary clones pBP-Rpi-blb3 and pKGW-Rpi-blb3, comprising the original genomic Rpi-blb3 gene construct and a Multisite Gateway® reconstituted Rpi-blb3 gene construct, respectively, were used as positive controls, and pBP-AbptGH-A as a negative control. Infiltrated leaves were challenged after two days with P. infestans strain PY23 or IPO-complex in detached leaf assays (DLA). Leaves infiltrated with pKGW-AbptGH-C, pBP-Rpi-blb3 and pKGW-Rpi-blb3 developed HRs at the inoculation sites whereas wildtype leaves and those infiltrated with pBP-AbptGH-A were susceptible to isolate PY23. As expected, all leaves inoculated with IPO-C were susceptible (FIG. 4). In view of these results, AbptGH-C was designated Rpi-abpt.

Cloning of R2 and R2-Like Through Blb3GH Allel Mining

Rpi-blb3 and Rpi-abpt belong to the major late blight (MLB) resistance locus on chromosome 4 that also harbors R2 and R2-like (Li et al., 1998; Park et al., 2005c). In view of the conserved marker order and observed allelic conservation between the genetic maps of Rpi-blb3, Rpi-abpt, R2, and R2-like (Park et al., 2005c), and the high sequence conservation between Rpi-blb3 and Rpi-abpt, we set out to clone R2 and R2-like through an Rpi-blb3 allele mining strategy. The same primers used to amplify the Rpi-abpt candidate gene from BAC clone TG92 were used to amplify full-length Blb3GH from the resistant parental genotypes BET95-4200-3 (MaR2) and AM3778-16, harboring R2 and R2-like, respectively. Amplicons of the expected size were cloned into pDONR221 and fully sequenced. In total, eight unique sequences were obtained from AM3778-16 (R2-likeGH) and nineteen from BET95-4200-3 (R2GH), with amino acid identities between Rpi-blb3 and the novel Blb3GH ranging from 86.4% to 97.3% for R2-likeGH and 83.8% to 94.2% for R2GH (Table 3). Phylogenetic analysis of all the available amino acid sequences clustered one R2like-GH and five R2GH in a clade together with the functional genes Rpi-blb3 and Rpi-abpt (FIG. 5). The amino acid sequence of R2-likeGH-8 shares 97.3% amino acid identity with Rpi-blb3. R2GH-2, R2GH-8, R2GH-G3, R2GH-D3 and R2GH-65 share 94.2, 91, 92.6, 89.7, and 92.8% amino acid identity with Rpi-blb3, respectively (Table 3). This set of candidate genes was targeted for functional analysis and therefore cloned into the binary vector pKGW-MG between the Rpi-blb3 promoter and terminator sequences, as described above for the Rpi-abpt gene.

Transient complementation assays in N. benthamiana showed R2GH-G3 and R2-likeRGH-8 to confer resistance to the appropriate races, whereas R2GH-2, R2GH-8, R2GH-D3 and R2GH-65 were non-functional (FIG. 4). R2GH-G3 and R2-likeGH-8 were therefore designated as R2 and R2-like, respectively.

Gene Structure and Functionality

Rpi-blb3, Rpi-abpt, R2 and R2-like encode ORFs of 2538-2544 nucleotides (nt) that code for proteins of 845-847 amino acids harboring all the signature sequences characteristic of LZ-NBS-LRR R-proteins (FIG. 6). Interestingly, with respect to known functional R-proteins, Rpi-blb3, Rpi-abpt, R2, and R2-like share the highest homology (34.9% aa identity) with RPP13 from Arabidopsis thaliana (Bittner-Eddy et al., 2000), which confers resistance to Hyaloperonospora parasitica. The highest homology with RPP13 resides in the NBS domain with 49.3% sequence identity, and the lowest within the LRR domains (34.3%). The LRR domains of Rpi-blb3, Rpi-abpt, R2, and R2-like are highly homologous and comprise 14 imperfect repeats (FIG. 6). The LZ and NBS domains are more polymorphic, those of R2 being the most divergent. Rpi-abpt and R2-like are identical except for the sequence between LRR2 and LRR3, where Rpi-abpt contains a stretch of amino acids that is identical to that of R2. The LRR domain of R2 is identical to that of Rpi-abpt, except for amino acid residue 774 (FIG. 6).

Alignment of the nucleotide sequences of the four functional genes and those of four additional Blb3GHs and subsequent analysis of informative polymorphic sites (IPS), i.e. sites where two or more genes carry the same nucleotide (Parniske et al., 1997), reveals clear blocks of sequence affiliation between different members of the gene family (FIG. 7), indicating that sequence exchange events between Blb3RGs have been involved in the evolution of the gene family (FIG. 7). Interestingly, the observed sequence affiliations in the 5′-terminal half of the genes extend throughout the LZ and NBS domains whereas sequence affiliations in the LRR domain suggest exchange of specific combinations of LRRs, underlining the modular nature of R-proteins.

In an attempt to assess the biological relevance of the observed sequence exchange events in relation to resistance spectrum, the parental clones harboring Rpi-blb3 (Blb99-256-3), Rpi-abpt (707TG11), R2 (BET95-4200-3(MaR2)) and R2-like (AM-3778-16) were challenged in detached leaf assays with 17 different P. infestans isolates (Table 4 and 5). For 14 isolates all four clones displayed the same specificity. However, differential interactions were observed with three isolates (Table 5). Isolates 99190 and 99189 are virulent on Blb99-256-3, AM-3778-16 and BET95-4200-3(MaR2) but avirulent on 707TG11-1. Moreover, isolate 99183 is virulent on BET95-4200-3(MaR2) and 707TG11, but avirulent on AM-3778-16 and Blb99-256-3. These data suggest that the four genes under study reflect three recognition specificities whereby Rpi-blb3 and R2-like share the same resistance spectrum. When taking in to account the observed sequence affiliations between Rpi-blb3, R2-like and Rpi-abpt, it is tempting to speculate that the polymorphic sequence between LRR2 and LRR3 could explain both the equivalent functionality of Rpi-blb3 and R2-like and the difference in resistance spectrum between R2-like and Rpi-abpt. Alternatively, the differential resistance spectra of the four clones may reflect the presence of additional R-genes.

Comparison of the amino acid sequences of the four functional genes with that of the non-functional sequence of R2GH-2, reveals that the majority of the R2GH-2 specific amino acids are concentrated in the putative solvent exposed residues of LRR11-LRR13 (FIG. 6), which reside within the 3′-most recombination block of the LRR domain (FIG. 7), suggesting that these LRRs play an important role in determining R2 specificity. However, presence of the R2 specific solvent exposed residues is not sufficient for R2 specificity as is illustrated by the non-functional homolog R2GH-D3, which contains the R2 specific LRR11-LRR13 sequence but differs from the four functional genes in the region harbouring LRR3-LRR10, which reside in the central recombination block of the LRR domain (FIG. 7). The latter observation illustrates the crucial role that putative intra-molecular interactions within the LRR domain and possibly between the LRR domain and the LZ or NBS domain play in determining functionality of the functional Blb3GHs.

Materials and Methods
Plant Material and Phytophthora Infestans Isolates

In this study we used the four late blight resistant clones Blb99-256-3, 707TG11-1, AM3778-16 and BET95-4200-3, harbouring Rpi-blb3, Rpi-abpt, R2-like, and R2, respectively. The potato cultivar Desiree was used for transformation. Wildtype Nicotiana benthamiana plants were used for transient complementation assays.

Characteristics and origin of P. infestans isolates used in this study are indicated in Table 4.

BAC Library Construction

Clones Blb99-256-3 and 707TG11-1 were used as DNA sources for the construction of BAC libraries. High-molecular weight DNA preparation and BAC library construction were carried out as described by Rouppe van der Voort et al. (1999). Approximately 74000 clones with an average insert size of 85 kb, corresponding to 8 genome equivalents, were obtained per library. The BAC clones were stored as bacterial pools containing approximatively 700 to 1000 white colonies. These were generated by scraping the colonies from the agar plates into LB medium containing 18% glycerol and 12.5 μg ml⁻¹chloramphenicol using a sterile glass spreader. These so-called super pools were stored at −80° C. Marker screening of the BAC libraries was done, first by isolating plasmid DNA from each pool using the standard alkaline lysis protocol and PCR was carried out to identify positive pools. Bacteria corresponding to positive pools were diluted and plated on LB agar plate containing chloramphenicol (12.5 μg ml⁻¹). Individual white colonies were picked into 384-well microtitre plates and single positive BAC clones were subsequently identified by marker screening as described by Rouppe van der Voort et al (1999). Names of BAC clones isolated from the super pools carry the prefix Blb (e.g. Blb25) or TG (e.g. TG9).

Subcloning of Candidate Genes

Candidate RGAs were subcloned from BAC clone BLB25 and TG9 as follows. Aliquots of approximatively 1 microgram BAC DNA were digested with 0.03U of Sau3Al restriction enzyme for 10 min. The partially digested BAC DNA was subjected to electrophoresis at room temperature in 0.5× TAE using a linear increasing pulse time of 1-10 sec and a field strength of 90 V cm−1 for 6 h. After electrophoresis, the agarose gel was stained with ethidium bromide to locate the region of the gel containing DNA fragments of approximately 10 Kbp in size. This region was excised from the gel and treated with GELASE (Epicentre Technologies, USA) according to the manufacturer. The size-selected DNA was ligated to the BamH1-digested and dephosphorylated binary vector pBINPLUS (Van Engelen et al., 1995) followed by transformation to ElectroMAX E.coli DH10B competent cells (Life technologies, UK).

Transformation of Susceptible Potato Variety

Binary plasmids harbouring the candidate genes were transformed to A. tumefaciens strain COR308 (Hamilton et al., 1996). After verifying their stability in Agrobacterium these clones were transformed to the susceptible potato variety Desiree. Overnight cultures of the transformed A.tumefaciens strain were used to transform internodal cuttings from in vitro grown plants (Heilersig, H. J. B et al., 2006). A total of 200 explants were used for each transformation. Primary transformants were transferred to the greenhouse.

DNA Sequencing and Computer Analysis

BAC clone sequencing was carried on using a shotgun cloning strategy. Sequencing reactions were performed using a dye terminator cycle sequencing reaction kit (Perkin-Elmer, Pt Biosystem, Warrington, UK), M13 universal forward and reverse primers, and an ABI377 automated sequencer (Applied Biosystem, La Jolla, Calif., USA). Sequence contigs were assembled using the ATADEN sequence and analysis program (Dear and Staden, 1991).

The binary subclones were sequenced using a primer walking strategy (700 bp by 700 bp). Gene structure was predicted using FGENESH++(Softberry). Multiple sequence alignments were conducted using CLUSTALX 1.81 (Thompson et al., 1997). Search of homologous genes to Rpi-blb3 was carried using the Basic Local Alignment Search Tool (BLAST). Conserved domains were identified using Swiss-Prot (InterProScan, EMBL-EBI, ExPASy, SAPS).

Resistance Assay

Detached leaf assays were used to determine the resistance phenotypes of primary transformants and N. benthamiana leaves. For complementation analyses, primary transformants were tested with isolates IPO-0 and 90128 (FIG. 2). Inoculum preparation and inoculation were performed as described by Vleeshouwers and associates (1999). Six days after inoculation, plant phenotypes were determined. Leaves showing no symptoms or a localized necrosis at the point of inoculation were scored as resistant and those with clear sporulating lesions as susceptible.

Transient Complementation in N. Benthamiana

Agrobacterium transient transformation assays (ATTA) were carried out on N. benmthamiana. Recombinant A. tumefaciens cultures were grown in LB medium (10 gram bacteriological peptone, 10 gram NaCl and 5 gram yeast extract in 1 liter MQ water) supplemented with 5 mg/L Tetracycline and 50 mg/L Kanamycin for the COR308 constructs. After one or two days a calculated amount of culture (according to OD 0.5 at 600 nm) was transferred to YEB medium (5 gram beef extract, 5 gram bacteriological peptone, 5 gram sucrose, 1 gram yeast extract, 2 ml 1 M MgSO4 in 1 liter MQ water) supplemented with Kanamycin for all strains. After 1 day overnight cells were centrifuged at 3500 rpm and re-suspended in MMA medium (20 gram sucrose, 5 gram MS salts and 1.95 gram MES) supplemented with 1 ml 200 mM acetosyringone to a final OD of 0.2 and infiltrated into 4 weeks old plants with a 3 ml syringe. Infiltrated leaves were subsequently challenged after two days with P. infestans strains IPO-complex and PY23 in detached leaf assays (DLA). Hypersensitive response (HR) or P.infestans sporulation were scrored from 4 to 8 days post inoculation.

Allele Mining

Primers of 32 nucleotides were designed on Rpi-blb3 sequence, with the forward primer beginning at the start codon (ATG) and the reverse primer beginning at the stop codon (TGA). BAC clone TG92-4-H3 containing Rpi-abpt and genomic DNA of the parental clones AM3778-16 and BET95-4200-3, containing R2-like and R2, respectively, were used as template in a long range PCR reaction (95 C: 2′40″, 30×[94 C: 20″, 56.8 C: 25″, 64.3 C:7′], 64.3 C: 25′) using the high fidelity DNA polymerase PfuTurbo® (Stratagene). PCR products were separated on agarose gel and purified using the QIAquick Gel Extraction Kit from Qiagen.

The purified pool of Blb3GHs were used in a BP reaction together with the donor plasmid pDONR 221 according to the protocol described by Untergasser et al. (http://www.untergassende/lab/protocols/bp_gateway_reaction_ii_v1_—0.sht ml). BP reaction products were transferred into DH10B E.coli competent cells, and subsequently plated on LB-agar plates containing the appropriate antibiotic. Transformed colonies were cultured o/n in LB liquid containing the appropriate antibiotic and plasmid DNA was isolated using a standard mini-prep protocol adapted from Sambrook et al (2^ndedition) using the P1, P2, P3 solutions from Qiagen. Clones harboring candidate Blb3GHs were cloned into the binary expression vector pKGW-MG, between Rpi-blb3 regulatory elements via a multiple LR reaction, using a pDONR-P4P1R plasmid harboring the Rpi-blb3 promotor, a pDONR-P2RP3 plasmid harboring the Rpi-blb3 terminator, and the pDONR221 plasmids harboring the candidate genes of interest. pKGW-MG plasmids harboring the genes of interest were then transferred to E.coli, and subsequently into a appropriate Agrobaterium tumefaciens strain, e.g. COR308 or AGL1, after the integrity of the constructs was checked by restriction analysis.

Tables

TABLE 1

R-genes and quantitative trait loci for late blight

resistance reported for wild Solanum species

Wild species
Locus type or name
Chromosome

S. berthaultii

QTLs (4)
I, III, VII and XI

Rpi-ber1
X

Rpi-ber2
VII

S. bulbocastanum

RB/Rpi-blb1
VIII

Rpi-blb2
VI

Rpi-blb3
IV

S. caripense

QTL (2)
unassigned

S. demissum

R1
V

R2
IV

R3, R6, R7
XI

R3a
XI

R3b
XI

R5-R11
XI

R10, R11
XI

S. microdontum

QTLs (3)
IV, V and X

QTL
Unassigned

S. mochiquense

Rpi-mcq1 (Rpi-moc1)
IX

S. paucissectum

QTLs (3)
X, XI and XII

S. phureja

Rpi-phu1
IX

S. pinnatisectum

Rpi-pnt1 (Rpi1)
VII

S. vernei

QTLs (several)
VI, VIII, IX

Hybrids with
Rpi-abpt
IV

S. tuberosum

R2-like
IV

QTLs (several)
several

QTLs
IV

TABLE 2

Overview of markers and primers used for mapping and

cloning

Marker
Type
PCR primer (5′ to 3′)
Tma
Enzymeb

Th21
SCAR
F: ATTCAAAATTCTAGTTCCGCC

a.s.

R: AACGGCAAAAAAGCACCAC

Blb22-S
CAPS
F: GTTTGATGTATGTTTGTTCTTGC
56
Msp1

R: TAATGCACTAATAACTAACTAGG

Blb22-T
SCAR
F: CTTTATTAGTTCCAAGAGCTAC
56

R: ACCCATCCCTTTTTCCTTATC

Blb25-S
CAPS
F: ACAGATGCTACGTCCATCAC
56
Alu1

R: CTCCACATGCGATGCAAAAAG

Blb25-T
CAPS
F: TTTCGATTATGGTGAGCCTTC
56
Hpy 188

R: TAGAAAAAGGGTGGTTGTGAC

RGH primers

RGH1
CAPS
F: GGSAAGACCACTCTTGCAAG
50
HpyCH4IV

R: GGTTTTTAAGCTGCTAATGTTG

RGH2
SCAR
F: GGSAAGACCACTCTTGCAAG
50
a.s.

R: TGGTYATAATYACTCTGCTGC

RGH3
CAPS
F: ATGRCTGATGCMTTTRTGTC
50
HaeIII

R: CCYAAGTASAGAAAACACTGC

4-PLOOP

F: GGiATGGGiGGiYTiGGiALRGAC
68

4-GLPL

R: TACiACAATiGCAAGiGGTAAMCC

4-GLO2

F: GTGTCTCTCAAGAGTACAACAC
56

R: GCTCGAACATCAAGTAGTTTCC

Blb3-start

F: ATGGCTGATGCCTTTCTRTCATTTG
55

Blb3-end

R: TCAGGAATCTCCTTTAAATTTGGAC

Blb3-prom

F: TCTTCCTTAGCATTCGTAGC
55

R: CTTTAGGAATACTAGTTTTGATTG

Blb3-ter

F: AGCTTTTCTGCCAAGCACATTGG
55

R: GTACCCTCCGTTTGTCGTTTGATC

Blb3-LRR-1-8

F: CTCTTTATGTATCAGACATGGC
55

R: CAACATCTTTCCACTGATCAC

Blb3-prom-end

F: CCCCAAGTTGTATAATGGTTG
55

Blb3-orf-bg

R: TGCTTGAGTGATTGAATCTCC

Sto-orf-bg

R: GGCCATATTCAGACTGGGAG

Blb3-spe

F: AGCTTTTTGAGTGTGTAATTGG
55

R: GTAACTACGGACTCGAGGG

TABLE 3

Amino acid sequence identity between Rpi-blb3 and Rpi-blb3 gene homologuess, including Rpi-abpt, R2 and R2-like.

blb3GH-B-
abptGH-C-
R2-likeGH-8-
R2GH-G3-
blb3GH-
abptGH-
R2-likeGH-
R2-likeGH-
R2-likeGH-
R2GH-
R2GH-

(Rpi-blb3)
(Rpi-abpt)
(R2-like)
(R2)
A
A
2
3
5
2
3

LZ-NBS-LRR
95.9
97.3
92.6
81.7
86.3
86.4
89.9
91.4
94.2
84.7

LZ
97.9
97.9
89.4
86.5
90.1
86.5
86.5
86.5
97.9
89.4

NBS
95.4
95.4
91
91.6
93.5
89.6
89.4
91.6
94.6
89.1

LRR
95.6
99.1
95.6
70
77.6
82.6
92.1
93.5
92.4
77.9

blb3GH-B-
R2GH-
R2GH-
R2GH-
R2GH-

R2GH-
R2GH-
R2GH-
R2GH-
R2GH-

(Rpi-blb3)
5
7
8
9

11
12
13
14
15

LZ-NBS-LRR
87.9
88.2
91
86.6

87
85
86.9
84
83.8

LZ
89.4
97.2
88.7
89.4

90.1
89.4
97.9
87.9
90.1

NBS
93.2
92.4
90.7
89.4

89.1
88.8
88.6
88.8
87.7

LRR
81.5
79.7
92.4
82.4

83.2
78.8
80.3
76.8
76.8

blb3GH-B-
R2GH-
R2GH-
R2GH-
LeBacGH-
LebacGH-
LeBacGH-
LeBacGH-
LeBacGH-

Rpi-

(Rpi-blb3)
16
D3
65
1
2
3
4
5
RPP13
blb1

LZ-NBS-LRR
86.7
89.7
92.8
75.6
55.7
70.9
78.3
47.6
34.9
24.4

LZ
87.9
88.7
89.4
80.9
81.6
77.3
78
52.5
31.9
19.9

NBS
89.1
89.9
92.1
80.1
57.5
81.2
86.4
53.7
50.1
32.4

LRR
83.2
92.1
95
67.4
42.6
56.5
69.4
40
23.2
20.6

indicates data missing or illegible when filed

TABLE 4

Characteristics of P. infestans isolates used in this study, and their putative virulence profiles.

Isolate
Year
Geographic origin
Mating type
Obtained from
Virulence profile

90128
1990
Geldrop, Netherlands
A1
Govers, Phytopathology WUR
1.3.4.7.8.11

USA618
unknown
Toluca Valley, Mexico
A2
Bill Fry, Cornell, USA
1.2.3.6.7.11

89148-09
1989
Netherlands

Govers, Phytopathology WUR
0

IPO-0

Netherlands

Kessel, PRI, WUR
0

IPO-C

Kessel, PRI, WUR
1.2.3.4.6.7.10.11

VK98014
1998
Veenkolonién, Netherlands
A1
Kessel, PRI, WUR
1.2.4.11

Dinteloord

Dinteloord, Netherlands

Kessel, PRI, WUR
1.2.4

EC1

Ecuador

Birch, SCRI, Scotland
3.4.7.11

F95573
1995
Flevoland, Netherlands
A1
Govers, Phytopathology, WUR
1.3.4.7.10.11

IPO-428-2
1992
Ede, Netherlands
A2
Kessel, PRI, WUR
1.3.4.6.7.8.11

Katshaar

Katshaar, Netherlands

Kessel, PRI, WUR
1.3.4.7.10.11

PIC 99177
1999
Metepec, Mexico

Kessel, PRI, WUR (Flier et al., 2002)
2.7

PIC 99183
1999
Metepec, Mexico

Kessel, PRI, WUR (Flier et al., 2002)
1.3.7

PIC 99189
1999
Metepec, Mexico

Kessel, PRI, WUR (Flier et al., 2002)
1.3.4.7.8.10

PIC 99190
1999
Metepec, Mexico

Kessel, PRI, WUR (Flier et al., 2002)
1.3.4.7

PY23*
1999
GGO

Govers, Phytopathology, WUR
1.3.4.7

*PY23: INF-1 non producing derivative of the wild type P.. infestans isolate 88069 (Kamoun et al; 1998; van West et al; 1999).

TABLE 5

Overview of resistance screening with a diverse set of P. infestans isolates

spp
Genotype
Gene
Chr.
py 23
IPO-0
90128
H30P04
VK98014
IPO428-2
Dintel
Katshaar

BLB
Blb8005-8
Rpi-blb1
8
R
R
R
R
R
R
R
R

BLB
Blb2002
Rpi-blb2
6
R
R
R
R
R
R
R
R

BLB
Blb99-256-3
Rpi-blb3
4
R
R
R
R
R
R
R
R

BLB
707TG11-1
Rpi-abpt
4
R
R
R
R
R
R
R
R

BLB
AM3778-16
R2-like
4
R
R
R
R
R
R
R
R

DMS
BET95-4200-3
R2
4
R
R
R
R
R
R
Rq
R

cv. Desiree
—
—
S
S
S
S
S
S
S
S

cv. Bintje
—
—
S
S
S
S
S
S
S
S

spp
Genotype
F95573
EC1
89148-09
99190
99183
99189
IPO-C
USA618
99177

BLB
Blb8005-8
R
R
R
R
R
S
R
R
R

BLB
Blb2002
R
R
R
R
R
R
R
R
R

BLB
Blb99-256-3
R
R
R
S

S
S
S
S

BLB
707TG11-1
R
R
R

S

S
S
S

BLB
AM3778-16
R
R
R
S

S
S
S
S

DMS
BET95-4200-3
R
R
R
S
S
S
S
S
S

cv. Desiree
S
S
S
S
S
S
S
S
S

cv. Bintje
S
S
S
S
S
S
S
S
S

R: resistant (incompatible interaction, no symptom or localized HR-like necrosis)

S: susceptible (compatible interaction, spreading lesion with sporulation)

Rq: intermediate phenotype (sporulation on 2 to 3 leaflets per compound leaf and localized HR on the other leaflets

DESCRIPTION OF THE FIGURES

FIG. 1. Genetic and physical map of the Rpi-blb3 (A) and Rpi-abpt (B) loci. Indicated are the relative positions of markers, the number of recombinants identified between markers, overlapping BAC clones that span the R-loci, and the relative positions of candidate genes (Blb3GH and AbptGH) that were targeted for complementation analysis.

FIG. 2. Genetic complementation for late blight susceptibility. Typical disease phenotype 8 days after inoculation with a sporangiospore suspension of Phytophtora infestans isolates 90128.

Blb-99-256-3: resistant parental clone; cv. Desiree: potato cultivar used for transformation; Blb25A-2-4 and Blb25A-2-5: primary transformants harboring RGH-Blb25A; Blb25B-2-1 and Blb25B-2-2: primary transformants harboring RGH-B1b25B (Rpi-blb3).

FIG. 3. Gateway strategy used to clone Rpi-abpt, R2 and R2-like. LR recombination of the three entry clones bearing the DNA fragments Rpi-blb3 promoter, candidate gene, and Rpi-blb3 terminator, with the Multisite Gateway destination binary vector pKGW-MG, leading to the functional gene expression clone.

FIG. 4. Transient complementation in Nicotiana benthamiana leaves. Typical disease phenotypes 7 days after inoculation with a sporangiospore suspension of P. infestans isolates IPO-0 (avirulent), 90128 (avirulent) and IPO-C (virulent on all except Rpi-sto) .

Control: wt N. benthamiana; pBP-Rpi-blb3: genomic Rpi-blb3 gene construct; pKGW-Rpi-blb3, -abpt, -R2-like, -R2, Rpi-sto1: multisite

Gateway gene constructs in which gene expression is regulated by the Rpi-blb3 promoter and terminator sequences.

FIG. 5. Phylogenetic tree based on the amino acid sequences of Rpi-blb3, Rpi-blb3 gene homologues amplified from late blight resistant potato clones harboring Rpi-abpt (AbptGH), R2-like (R2-likeGH) or R2 (R2GH), RGHs present on the tomato BAC clone AF411807, RPP13-Nd and Rpi-blb1. Boxed is the group containing Rpi-blb3, Rpi-abpt, R2 and R2-like.

FIG. 6. Amino acid sequence alignment of Rpi-blb3, Rpi-abpt, R2-like, R2, and a non functional R2 gene homologue R2GH-2. The full amino acid sequence of Rpi-blb3 and homologues is shown. Indicated are the 14 LRR repeats (1-14), in which the leucine(like) residues have been shown in bold.

FIG. 7. Sequence affiliation analysis between Rpi-blb3 gene homologues. Depicted are only informative polymorphic sites (IPS) of the nucleotide sequences of 7 Rpi-blb3 homologs, including Rpi-blb3, Rpi-abpt, R2 and R2-like. The vertical number at the top of each column indicates the corresponding nucleotide position in the full consensus sequence. Highlighted are the IPS that are different from the Rpi-blb3 sequence. Indicated at the bottom is the domain from which each IPS is from (LZ, NBS or LRR) and also relative positions of four putative recombination blocks (region A-D)

FIG. 8. Nucleotide sequence of clone Blb25-B2 (8461 bp) containing the Rpi-blb3 gene and regulatory sequences. The Rpi-blb3 coding region of 2544 by is highlighted in lower case (2944-5487). The upstream 2732 nt (211-2942) and the downstream 882 nt (5488-6370) harbour the regulatory sequences.

FIG. 9. Nucleotide sequence of the cds of Rpi-abpt.

FIG. 10. Nucleotide sequence of the cds of R2.

FIG. 11. Nucleotide sequence of the cds of R2-like

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FUNCTIONAL R-GENE FROM SOLANUM BULBOCASTANUM

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