Plant defense-related genes regulated in response to plant-pathogen interactions and methods of use

Abstract

Compositions and methods of use for the expression of plant pathogen defense-related and signaling genes are provided. The compositions include nucleotide sequences identified from tomato that show specific patterns of gene expression associated with the Avr-Pto mediated defense response in tomato plants resistant to bacterial speck disease caused by Pseudomonas syringae pathovar tomato [strain T1(A)]. The nucleotide sequences are specific to genes that are up-regulated or down-regulated in response to the interaction of AvrPto and Pto in the presence of Prf. These compositions have agricultural utility for increasing resistance to a variety of biotic and abiotic stresses, including plant pathogens.

Description

BACKGROUND OF THE INVENTION

[0003] 1. Field of the Invention

[0004] The invention pertains to the field of genetic engineering of plants. More particularly, the invention pertains to the genetic manipulation of plants, through transformation and\or breeding, by expressing or manipulating the regulation of expression of certain polynucleotides that enhance plant disease resistance.

[0005] 2. Description of the Related Art

[0006] Biotic stress is major cause of loss in yield and quality of crop produce. It is caused by infection by plant pathogens, infestation by insects and other pests and parasitism by another organism. Developing plants that can resist or tolerate biotic and/or abiotic stress impacts positively on the quality and yield of crop plants. Understanding of the molecular mechanisms used by plants to resist, tolerate or avoid biotic and/or abiotic stress provides new strategies of crop improvement for stress tolerance.

[0007] Plants possess defense mechanisms, which enable the plants to prevent or limit the spread of plant pathogens. For example, in response to pathogen infection, plants trigger a cascade of signal transduction pathways that result in the activation of a defense response. Two types of relatively well-characterized defense responses are: 1) localized defense response, called the hypersensitive (HR) response, and 2) systemic response induced by signaling molecules moving from a location of infection to uninfected parts of a plant (systemic acquired resistance) or systemic induction of proteinase inhibitors (systemic wound response). The products of such induction of defense responses are known to enhance resistance against a broad range of biotic and/or abiotic stresses. Polynucleotides encoding such gene products can be used to enhance resistance to biotic and/or abiotic stresses, through various strategies, which are well known in the art, such as, for example, genetic engineering (e.g., transformation by, for example, particle bombardment or Agrobacterium-type vectors) and\or marker assisted breeding methods.

[0008] Resistance to bacterial speck disease is mediated by the dominant Pto gene in tomato and the corresponding avirulence gene avrPto in Pseudomonas syringae (Ps) pathovar tomato [strain T1(A)]. Pto, isolated by a mapped-based cloning strategy (Martin et al. 1992), encodes a protein kinase (Loh and Martin 1995), which is the molecular receptor for the bacterial avirulence factor encoded by the avrPto gene (Tang et al. 1996). Yeast two hybrid screens indicate that Pto interacts with and phosphorylates another protein kinase (Ptil; Zhou et al. 1995) as well as transcription factors (Pti 4/5/6) that directly bind to an element in the promoter region of defense-related genes (Zhou et al. 1997). The insecticide fenthion elicits an HR-like response, similar to that induced by avirulent bacteria, with this phenotype being conditioned by the highly similar and closely linked gene Fen (Martin et al. 1994). Expression of both sensitivity to fenthion and resistance to Pseudomonas strain T1(A) requires the action of another tomato gene, Prf, indicating a potential convergence of signal transduction pathways for the two phenotypes (Salmeron et al., 1996). Rapid and genotype-differential defense gene expression can be detected after both treatments within 4 hr (Halterman, 1999; Jia and Martin, 1999). A model of response to bacterial speck disease and fenthion treatment has been described by Zhou, et al. (1997).

SUMMARY OF THE INVENTION

[0009] Methods and compositions for expression in plants, or manipulation of expression of plant pathogen defense-related and signaling genes are provided. The compositions comprise nucleotide sequences identified from tomato that show specific patterns of gene expression associated with the Avr-Pto mediated defense response in tomato plants resistant to bacterial speck disease caused by Pseudomonas syringae pathovar tomato [strain T1(A)]. Some of the nucleotide sequences are specific to 227 genes that are induced in response to the interaction of AvrPto and Pto in the presence of Prf, while others are specific to 129 genes that are down-regulated in response to the interaction of AvrPto and Pto in the presence of Prf. The compositions find use in agriculture, especially for increasing resistance of plants to a variety of plant pathogens, methods of modifying the signaling pathways and methods of inducing specific genes or decreasing expression of specific genes, resulting in a favorable resistance response in the plants. Methods for regulating the expression of a gene in response to a stimulus also are provided. The methods comprise stably transforming the genome of plants with the nucleotide sequences of the invention operably linked to a suitable promoter that drives the expression in a plant cell, and decreasing expression of the nucleotide sequences of the invention. Methods for marker assisted selection in breeding strategies also are provided.

BRIEF DESCRIPTION OF THE DRAWING

[0010] FIGS. 1A and 1B show an illustration of trace indexing, as used for identification of specific nucleotides at a specific position immediately following a restriction-site of the cDNA fragment. See Materials and Methods for details on the trace indexing process. The color of the trace indicates the last nucleotide of the unlabelled primer used in the competitive PCR reaction (blue=A, Red=C, Green=G and black=T). FIG. 1A—Identification of the nucleotides in R2 position. FIG. 1B—Identification of the nucleotides in J2 position. The detected nucleotides of the corresponding cDNA fragments are indicated next to each peak in the digital images.

[0011] FIG. 2 shows a chart depicting the various experimental treatments used to treat leaves.

[0012] FIG. 3 shows a chart depicting a Pseudomonas syringae disease response model.

[0013] FIG. 4 shows a chart depicting the CuraGen GeneCalling procedure.

[0014] FIG. 5 shows a cartoon depicting the GV2260 Agro transient assay.

[0015] FIG. 6 shows a graphic map of the pQuiet2 vector used for VIGS.

[0016] FIG. 7 shows a graphic representation of the PCR method, illustrating how the VIGS library was normalized to reduce the frequency of highly expressed genes.

[0017] FIG. 8 shows a graphic representation of the “VIGS strategy” used for library screening.

[0018] FIG. 9 shows a graph of the resistance response for induced or up-regulated genes.

[0019] FIG. 10 shows a graph of the resistance response for suppressed or down-regulated genes.

[0020] FIG. 11 shows the resistance response for an induced gene in the jasmonic acid synthesis pathway.

[0021] FIG. 12 shows Northern blot hybridization data using clones for a subset of the polynucleotide sequences of the invention. Plant samples from PtoR (R), PtoS (S) and Prf-3 were used in the RNA-gel blots at 0, 2, 4 and 8 hours after infection by the pathogen, Pseudomonas syringae pathovar tomato [strain T1(A)].

[0022] FIGS. 13 A-S shows the phenotypes of several plants wherein VIGS was used to silence specific genes modulated in the resistance response.

DETAILED DESCRIPTION OF THE INVENTION

[0023] Materials and Methods

[0024] 1. Plant Material and Treatments

[0025] Tomato seeds were placed on Whatman paper in Petri plates to ensure uniform germination. Germinated seeds (8 for each treatment, 96 total,) were planted singly in 1″ cells and grown for ˜2 weeks. Eight uniform plants per treatment were transplanted into 5″ pots, with 2 plants in each pot (4 pots per treatment). This planting schedule was repeated 3 consecutive weeks to allow for repetition of the entire experiment if necessary. However, all plant material processed was result from a single experimental cohort. Approximately 2 weeks after repotting, plants were subjected to several different treatments. Three tomato genotypes were infiltrated with the avirulent bacteria T1(A). Rio Grande Pto-R (RG Pto-R) responds with a macroscopic HR after ˜8-12 hr. The ptoS genotype has a single nucleotide mutation in Pto, causing these plants to respond with visible disease symptoms after ˜18 hr. Finally, plants with the prf-3 mutation have a ˜1 kb deletion in the Prf gene, disrupting the Pto pathway and resulting in susceptibility. The ptoS and prf-3 mutations are in the RG Pto-R genotype and the plants are thus isogenic. Plants were vacuum infiltrated as described (Jia and Martin, 1999) and brought back to the greenhouse for 4 hours. Control plants were infiltrated with buffer only. RG Pto-R were also vacuum infiltrated with a solution of fenthion (Halterman, 1999). As a control to identify expression induced by fenthion (but not related to the Pto pathway), the prf-3 mutant line was also be infiltrated with fenthion. At the appropriate time point following each treatment, leaf tissue from the two plants in a pot (avoiding both the youngest and oldest leaflet) was harvested together, placed in liquid nitrogen, and stored at −80 C. This was repeated for three (of the four total) pots for each treatment, resulting in three replicates. The fourth pot was saved so that the expected phenotype can be confirmed. RNA was then be isolated from 3-5 grams of tissue by the hot phenol method (Jia and Martin, 1999). The quality of the RNA preparation was assessed by formaldehyde gel-electrophoresis and spectrophotometry, and then stored in 70% ethanol.

TABLE 1
Experimental samples and treatments
Tomato				Treatment
genotype	Treatment	Time point	Replicates	Notation
RG Pto_R	T1(A)	4 hr post infiltration	3	PtoR_T1A
	2.2 × 107
ptoS	T1(A)	4 hr post infiltration	3	ptoS_T1A
	2.2 × 107
prf_3	T1(A)	4 hr post infiltration	3	prf3_T1A
	2.2 × 107
RG Pto_R	fenthion	4 hr post infiltration	3	PtoR_Fn
prf_3	fenthion	4 hr post infiltration	3	prf3_Fn
RG Pto_R	vacuum	4 hr post infiltration	3	PtoR_Ctrl
	infiltration
	(control)

[0026] 2. RNA Profiling Analysis

[0027] RNA profiling studies were conduced using GeneCalling. GENECALLING™ is a differential expression analysis, RNA profiling technology, which is described in U.S. Pat. No. 5,871,697 and in Shimkets et al., Nature Biotechnology 17:798-803 (1999), the complete disclosures both of which are hereby incorporated herein by reference in their entirety. Poly-A mRNA was isolated from each of the RNA samples and double-stranded cDNA was synthesized from each of the poly-A mRNA samples (Shimkets, et al., 1999). Each cDNA sample was subjected to digestion with 96 pairs of restriction endonucleases. The digested product was ligated to two specific adapters at each end and subjected to quantitative PCR amplification using two primers labeled with FAM (J-primer) and Biotin (R-primer) specific to the two adapters (Bruce et al., 2000). After electrophoresis of the PCR-amplified product, the relative intensity of the cDNA fragments was measured by laser excitation of the FAM-label. DNA fragments of known sizes (sizing-ladder) were simultaneously electrophoresed to accurately (±0.1 base pairs) determine the sizes of the cDNA fragments. The electrophoresis data were stored as digital gel images with the relative intensity of the cDNA fragments in the Y-axis and the fragment size in base pairs in the X-axis. The RNA profiling was repeated three times for each cDNA sample.

[0028] Pair-wise in silico comparisons were made between the treatments using the digital trace images to identify cDNA fragments modulated at least 2-fold. The replicated data were used to calculate the statistical significance of the difference, as described in prior publications (Shimkets, et al., 1999; Bruce et al., 2000). Secondary comparisons were made using the data from specific pair-wise comparisons to identify specific gene expression patterns associated with a biological response.

[0029] The PCR-amplified product from the four treatments was subjected to Trace Indexing (see FIG. 1) to obtain additional nucleotide sequences of the cDNA fragments. Trace Indexing was done using a competitive PCR procedure (Shimkets et al., 1999 and Bruce et al., 2000), which involved re-amplification of the PCR product from RNA-profiling under same conditions, except with the addition of an unlabeled oligonucleotide primer. The unlabeled primers were designed such that each group of primers were identical to the labeled primers (J- and R- primers) except that the 3′ end of the primers were extended to include one (A, T, G or C) or two (NA, NT, NG or NC) nucleotides immediately following the unique restriction-site at each end (J and R). A total of four groups of such unlabeled primers were designed (J1, J2, R1 and R2). The digital trace-images obtained by 4 different unlabelled primers within a group were superimposed to detect the specific nucleotides at a specific position immediately following the restriction site of the cDNA fragments, by observing which of the four primers oblate the peak intensity of a given band in a trace. Likewise, the bands in a given digital trace of a treatment were indexed for up to four additional nucleotides, based on the oblation of the intensities of the corresponding fragments by specific unlabeled primers.

[0030] The differentially modulated cDNA fragments were classified into known and novel genes by querying the available GenBank tomato sequence database using the data on fragment size (base pairs) and the restriction-site specific sequences for every cDNA fragment. The list of genes thus identified was further evaluated using the data from Trace Indexing. The confidence on the association of the known gene with the cDNA fragments was derived from the total number of additional nucleotides matched between the gene and all associated cDNA fragments, using the nucleotide data from trace indexing. The genes with maximum number of nucleotide matches from all associated cDNA fragments were selected as putative defense-related genes. The cDNA fragments without a significant association with known genes were annotated as putative novel genes and were cloned and sequenced. The association of a cDNA fragment with known or novel sequence was finally confirmed by the competitive PCR-method with an unlabeled oligonucleotide primer containing 20 to 23 nucleotides of sequence specific to the known or novel sequence associated with the cDNA fragment. The confirmation that the cDNA fragment is part of the sequence was obtained when the unlabeled oligonucleotide successfully competed with the labeled primer and oblated the intensity of the cDNA fragment of interest, while the intensities of the remaining cDNA fragments in the digital gel image were the same as those in the original gel image (Shimkets et al., 1999 and Bruce et al., 2000).

[0031] 3. Virus-Induced Gene Silencing (VIGS)

[0032] One very powerful method for studying gene function is post-transcriptional gene silencing [PTGS; also known as RNA interference (RNAi)]. We used virus induced transient gene silencing (VIGS) to determine the role of differentially modulated genes, identified through GeneCalling, in disease resistance. Transient VIGS, based on potato virus X (PVX), is a technically simple and rapid method to assess function of genes in the Solanaceae. This method relies on the construction of a PVX derivative that contains the plant gene of interest (e.g., differentially modulated gene fragment obtained through GeneCalling) targeted for silencing. When the transgenic virus infects a plant, a double-stranded RNA species is formed which triggers sequence-specific gene silencing. PVX-based gene silencing has been shown to be especially effective in Nicotiana benthamiana. N. benthamiana is an excellent surrogate species for studying defense responses of tomato because its large fleshy leaves lend themselves to infection by many of the same pathogens that attack tomato (e.g., Pseudomonas, Phytophthora). Another advantage of N. benthamiana is that the tomato Pto gene is functional in this species, and therefore the Pto-AvrPto interaction can be easily studied using an Agrobacterium-based transient assay. Hence, we performed our VIGS assays in N. benthamiana.

[0033] In order to genetically dissect the Pto-mediated disease resistance pathway, a Fast-Forward genetics strategy based on Virus-Induced Gene Silencing (VIGS) was developed. We constructed a Nicotiana benthamiana (Nb) cDNA library in a PVX-based vector. We chose Nb instead of tomato for two simple reasons: silencing is more straightforward and the Pto/avrPto signaling pathway is conserved in this species. The Nb Mixed Elicitor cDNA (cNbME) library was made with Nb tissue treated with different abiotic elicitors (Salicylic Acid, Jasmonic Acid, ethylene) and undergoing Pto/avrPto mediated hypersensitive response (HR), Ps pv. tomato T1-mediated non-host HR, disease caused by Ps p.v tabaci and tissue expressing transiently avrPto (to analyze avrPto virulence-response).

[0034] Two time points for each treatment were included, as well as control or untreated tissue. RNA samples were extracted, analyzed for RNA quality control and pooled for mRNA purification. The cDNA library was constructed following the SSH method (Clontech, PCR-Select kit) with some modifications: the cDNA population was normalized instead of subtracted, size selected (0.3-1. Kb) and the inserts were made compatible with the gateway cloning system. The library was cloned in a PVX-based vector, which includes a mini-binary vector with the PVX cDNA sequence cloned within the T-DNA region and under control of the CaMV 35S promoter. NbME cDNAs were cloned within the PVX cDNA between the triple block and the Coat Protein via Gateway Reaction (yielding a chimeric virus) and the library was transformed into Agrobacterium tumefaciens (GV2260 strain).

[0035] Biotic treatments used to induce defense responses in leaf tissue include: AvrPto-Pto HR and AvrPto-dependent virulence (transient assay using EHA105); Agro (35S::avrPto)+ Agro (35S::Pto); Agro (35S::avrPto). Each Agro culture was diluted to OD600=0.2, mixed with the same volume and hand infiltrated with a syringe. Time points taken were 24 and 48 hours postinfection. For the non-host HR treatment, P. syringae pv. tomato T1 (titer 10 8) time points were 4 and 18 hours post-infiction, and P. syringae pv. tabaci and P. syringae pv. tabaci (avrPto) (titer 10 6) time points were 24 and 72 hours postinfection. Tissue silenced with PVX::PP2A was also included.

[0036] Elicitor treatments included INA 1.3 mM: 4, 24 h, (foliar spray application, incubation in Petri dish with lid at lab bench [INA=CGA41396 from CIBA]; Jasmonic acid 100 μM: 4, 12 hours (foliar spray application, incubation in closed chamber); Ethylene 50 ppm: 2, 12 hours (sealed chamber incubation). An equal amount of tissue from each time point/treatment was pooled and mRNA was obtained.

[0037] Amplicon vector pQ2 includes a 5′ modified PVX vector derived from pP2C2S (obtained from D. Baulcombe) in pOP8 mini-binary vector and converted into the gateway system. pOP8 derives from the mini-binary vector pCB302-3, in which the bar gene in the T-DNA region has been replace with the nptII gene and the multicloning site has been modified to make it compatible with PVX cloning sites.

[0038] For screening of the cNbME library and silencing Nb to identify genes involved in Pto-mediated disease resistance, Nb seedlings were agro-infected by pricking the leaves with a toothpick. The chimeric virus infects the plants, spreads and silencing develops after 2½ to 3 weeks. Two plants were infected/clone and two well-silenced leaves/plant were screened and scored for any alterations in:

[0039] Pto-mediated HR (co-agro-infiltration of cultures that carry a 35S::Pto and 35S::avrPto plasmid; agro-infiltration of the constitutively active Pto mutant Pto(Y207D);

[0040] Chlorosis generated by avrPto-mediated virulence (agro-infiltration of 35S::avrPto); or

[0041] Disease response caused by Ps pv tabaci.

[0042] In parallel, Nb plants were infected with PVX (empty vector, negative control), PVX::prf (positive control; prf is necessary for the Pto-mediated HR in Nb, its silencing abrogates Pto-mediated HR) and PVX::pds to assess the quality and timing of the silencing process (pds=phytoene desaturase; plants silenced for this clone develop photobleached leaves). The identity of any clone that gave any alteration in the responses listed above compared with the control plant (infected with the empty PVX vector) was determined by sequencing. At least 2,400 clones were screened initially, and approximately 130 clones were initially identified that gave any alteration in any of the responses scored.

[0043] A subset of 130 clones were selected (based on clone ID and on % of response inhibition) and cloned into a Tobacco Rattle Virus-based (TRV) silencing vector, in order to confirm and further characterize the phenotype conferred.

[0044] Two new assays were added:

[0045] Cf9/Avr9 HR (co-agro-infiltration of cultures that carry a 35S::Cf9 and 35S::avr9 plasmid), to determine Pto pathway specificity.

[0046] Ps pv tomato T1 (high titer) for non-host HR.

[0047] An average of 6-8 independently silenced plants/clone (two leaves/plant) were screened in each experiment and the results of the screening were compared with the controls (empty TRV infected plants and TRV::prf silenced plant). In most of the experiments, partial inhibition in the Pto+avrPto response was observed in the control plants (empty TRV vector infected plant). The % shown in the table for Pto-mediated HR inhibition represents the % of the inhibition above the % in control plants.

[0048] Results

[0049] 1. RNA Profiling Analysis

[0050] Table 2 shows the comparisons made between the samples to identify cDNA fragments differentially modulated. Secondary comparisons were made to identify a subset of the cDNA fragments specifically induced in plants expressing the defense response genes (PtoR_T1A). The Genbank EST sequences that were identified to be associated with these fragments were used in competitive PCR to confirm the association of these genes with cDNA fragments identified. The sequences of the cDNA fragments, as confirmed by competitive PCR, are disclosed herein (see Sequence Listing).

TABLE 2
List of primary comparison made to identify cDNA-fragments
differentially modulated
	cDNA Fragments
		Total	Differentially
Job ID	Primary Comparison*	Assayed	Modulated**
29612	PtoR_T1A vs. PtoR_Ctrl	32995	3657	(11.1%)
29632	PtoR_T1A vs. pfr3_T1A	33935	2184	(6.4%)
29652	PtoR_T1A vs. ptoS_T1A	34380	1845	(5.4%)
29672	PtoR_Fn vs. ptoS_Fn	34779	435	(1.3%)
29692	PtoR_Fn vs. PtoR_Ctrl	32488	1022	(3.1%)
32992	PtoR_T1A vs. PtoR_Fn	32815	3315	(10.1%)
33012	PtoR_T1A vs. PtoS_Fn	33557	3319	(9.9%)
33032	PtoR_Fn vs. ptoS_T1A	35073	1373	(3.9%)
33052	PtoR_Fn vs. prf3_T1A	34196	897	(2.6%)
33072	PtoR_Ctrl vs. ptoS_T1A	34461	1524	(4.4%)
33092	PtoR_Ctrl vs. prf3_T1A	34032	904	(2.7%)
33112	PtoR_Ctrl vs. ptoS_Fn	34024	1400	(4.1%)
33132	ptoS_T1A vs. prf3_T1A	36686	293	(0.8%)
33134	ptoS_T1A vs. ptoS_Fn	36725	1256	(3.4%)
33152	prf3_T1A vs. ptoS_Fn	35859	1474	(4.1%)
*Annotations for samples are described in Table 1.
**minimum N-fold = 2, P-value = 0.15, values in the parentheses are percent of the total fragments assayed.

[0051] Certain aspects of the invention are published in an article entitled Comprehensive transcript profiling of Pto- and Prf-mediated host defense responses to infection by Pseudomonas syringae pv. tomato, in The Plant Journal (2002) 32, 299-315 (and Supplemental Discussion thereof), the complete disclosure of which is hereby incorporated herein by reference in its entirety. The article details the identification of 432 genes that are modulated in tomato plants, in the resistance response to Pseudomonas syringae pathovar tomato [strain T1(A)].

[0052] 2. Identification of Functional Classes of Genes

[0053] We have identified and disclose herein 227 genes that are induced or up-regulated in the resistance response, specific to the response involving the interaction of AvrPto, Pto, and Prf. The expression data for these genes are provided in the Table 2 of Provisional Application No. 60/348,792, filed Jan. 14, 2002, entitled “PLANT DEFENSE RELATED GENES AND METHODS OF USE,” and are incorporated herein by reference. The sequences for these genes are provided in the Provisional Application as Appendices: Appendix 1 contains 197 sequences that were identified from the public database, Appendix 2 contains 30 sequences that were identified in house through cloning and sequencing, and Appendix 3 contains 16 sequences representing a subset of the 30 in house gene sequences that were extended using ESTs from the public database.

[0054] The 227 up-regulated genes were annotated using BLAST results from the public database. These annotations were used to classify the genes based on the proposed functional role of these genes. We have rank ordered the genes based on their functional role: 14 sequences were classified as novel, 35 sequences were classified as unknown, 28 sequences were classified in signaling pathways, 18 sequences were classified as transcription factors, 5 sequences were classified as hormone responsive, 3 sequences were classified in the Jasmonic acid biosynthesis pathway, 2 sequences were classified in the oxidative burst pathway, 24 sequences were classified as general plant-defense-related, 5 sequences were classified as proteases, 1 sequence was classified in the Shikimate pathway, 2 sequences were classified in ubiquination pathway, and 14 sequences were classified in the phenylpropanoid pathway. The remaining 76 sequences were classified in other function roles.

[0055] We also identified and disclose herein 129 genes that are down-regulated in the defense response, specific to the response involving the interaction of AvrPto with Pto, and\or Prf. The expression data for these genes are provided in Table 2 of Provisional Application No. 60/390,249, filed Jun. 20, 2002, entitled “PLANT DEFENSE RELATED GENES REGULATED IN RESPONSE TO PLANT-PATHOGEN INTERACTIONS AND METHODS OF USE,” and are incorporated herein by reference. Of the 129 down-regulated genes described, 125 were found in the public database, while the remaining 4 sequences were identified in house, through cloning and sequencing. These genes were annotated using BLAST results from the public database. These annotations were used to classify the genes based on the proposed functional role of the genes. We grouped these genes based on their functional role in Table 2 of the Provisional Application.

[0056] Several classes of these genes contribute to our understanding of the resistance response, and are described below.

[0057] Cell wall reinforcement: Phenylpropanoids have been proposed to serve as flower pigments (anthocyanin), UV protectants, defense chemicals (phytoalexins, insect repellents), allelopathic agents, and signal molecules in plant-microbe interactions. Furthermore, phenylpropanoids are the building units of polymeric support structures, such as lignin or lignin-like cell wall components. This study revealed that almost 4% of the resistance response genes belong to phenylpropanoid pathway (includes 4 anthocyanin biosynthesis genes) and they are induced during plant defense. Cell wall reinforcement and thickening is associated with plant defense during resistance response. In our study we have shown that, along with phenylpropanoid genes, other cell wall thickening genes are up-regulated and most of the genes encoding cell wall degrading enzymes are down-regulated during the resistance response.

[0058] Programmed Cell Death: Programmed cell death (PCD) constitutes the main form of cell death in animals, plants and other organisms. In plants PCD is a typical phenomenon during hypersensitive response triggered by an incompatible plant pathogen interaction. In this study we have shown that 4 PCD related genes are induced during the resistance response. The Arabidopsis LSD1 gene encodes zinc-finger type transcription factor that acts as a negative regulator of hypersensitive induced plant cell death. In this study we have shown that a tomato gene homologous to LSD1 is induced during the resistance response. Thus, it appears that the cells neighboring the infected cell are trying to suppress cell death by up-regulating the anti-death pathway. In contrast, a gene homologous to apoptosis antagonizing transcription factor (AATF) is down-regulated during the resistance response.

[0059] Senescence: PCD leads to senescence and we saw that genes encoding senescence related proteins like thiolase, cysteine protease, ascorbate oxidase and certain transcription factors were up-regulated as part of the plant defense mechanism. Overlap between the leaf senescence and pathogen-defense programs have been reported in the literature. Obvious visual symptoms of leaf senescence are loss of chlorophyll pigments due to decline in photosynthesis and chloroplast disintegration. It has been suggested that in cells undergoing HR, a decline in photosynthesis might act as an inducer of senescence. In this study, we show that certain chloroplast-associated transcription factors that are believed to be negative regulators of chloroplast gene expression are induced during the resistance response. These data indicate that the plant is shutting down the chloroplast as part of the defense mechanism, apparently to initiate senescence.

[0060] Oxidative burst: The oxidative burst that precedes PCD has been suggested to be a primary event responsible for triggering the cascade of defense responses in various plant species against infection with avirulent pathogens or pathogen-derived elicitors. Here we show that a tomato gp91-phox gene, along with a 2-nitropropane dioxygenase-like gene that is involved during oxidative burst, are induced during Pto mediated disease resistance.

[0061] Cell protectants: The oxidative burst may be followed by activation of genes encoding antioxidant enzymes in tissue surrounding the initial infection site to protect the surrounding cells against oxidative damage. We found that several of these cell protectant genes, such as annexin, peptide methionine sulfoxide reductase, glutathione peroxidase and glutathione S-transferase, are induced during the resistance response. Alkaloids are antimicrobial compounds that defend cells against pathogen attack. Using GeneCalling, we have shown that two genes involved in alkaloid biosynthesis are up-regulated during the resistance response.

[0062] Ubiquitination pathway: An interesting class of genes that is differentially expressed during plant disease resistance response are the genes involved in the ubiquitination pathway. Much speculation has been made by other research groups about the role of ubiquitination pathway during R gene mediated disease resistance. In animals, protein ubiquitination is not only essential for the normal physiological turnover of proteins, but also appears to have been adapted as part of an intracellular surveillance system that can be activated by altered, damaged, or foreign proteins and organelles. Here we show that certain genes, such as ubiquitin and ubiquitin activating enzyme, involved in ubiquitination-mediated protein degradation, are induced during Pto mediated disease resistance. In addition to induction of the ubiquitination pathway, several proteases are induced that also appear to target the degradation of pathogen effector proteins that enter the plant cell.

[0063] Water transport: Water is essential for pathogen multiplication in the plant tissue. One of the Pst disease symptoms is water soaked lesions on tomato leaves. Water is almost certainly essential to produce these symptoms. Here we show that aquaporin 1, aquaporin 2, ZmSIP2-1 and PIP2-1, genes involved in water transport, are suppressed during Pto mediated disease resistance.

[0064] Protein synthesis: Plant cell machinery undergoes tremendous stress during a defense response to make necessary plant defense-related proteins. All these extra proteins have to be made in a very short time and hence require efficient translation machinery. Here we show that 2 out of 3 protein synthesis genes, identified to be differentially expressed, are induced during the resistance response.

[0065] Signaling: Signaling is an essential part of any biological process. Since plant defense mechanisms are very complicated processes involving numerous protein-protein interactions, signaling plays a vital role. In this study, we have shown that 18 different kinases and 4 phosphatases are induced during the resistance response.

[0066] Stress-related genes: Stress-related genes are generally induced in response to any external stimulus. They are induced to activate the plant defense mechanism against any external stimulus. Here we have shown that several general stress-related genes, such as heat shock proteins, are induced during the resistance response.

[0067] Transport: Transport of nutrients and ions across cell membranes plays a major role in maintaining cellular homeostasis. Maintaining cellular homeostasis is a real challenge when a plant is under stress. We have found that several proteins involved in nutrient or protein transport are induced during the resistance response.

[0068] Transcription factors: The most striking observance among the resistance response genes is the preponderance of transcription-factor-related genes. The rapid induction of these genes suggests that they are integral members of an early-response plant defense network under Pto and Prf control. EREBP transcription factors are members of a large family of transcription factors thought to control expression of many genes during the defense responses induced by a number of biotic and abiotic stresses. It has been suggested that EREBPs regulate the expression of the genes encoding them via interaction with GCC boxes (found in promoters of several PR genes) in their promoters. In this study we have shown that EREBP protein encoding genes Pti4, a Pti4 homolog and Pti6 genes are induced during the resistance response. Two other genes encoding EREBP like proteins also are induced during the resistance response. WRKY proteins have recently been identified as a new family of transcription factors. They have been shown to have regulatory function in response to pathogen infection and other stresses. We identified 4 genes that encode WRKY domain-containing transcription factors, and all of them are induced during the resistance response. SCR is a member of a novel class of transcription factors with similarity to the basic domain of the basic-leucine zipper (bZIP) transcription factors. SCR regulates asymmetric cell division that is essential for generating the radial organization of the Arabidopsis root. Five genes encode SCARECROW (SCR) like transcription factors and all of them are induced during the resistance response. To our knowledge, this is the first report showing the involvement of SCR-like transcription factors in plant defense. NAC domain-containing proteins are a novel class of transcription factors to which belongs the ATAF subfamily of transcription factors. Several NAC domain-containing transcription factors have been implicated to play a role in plant defense. NAC proteins have been shown to directly interact with plant viral proteins to confer resistance against certain viruses. In this study, we have shown that two NAC domain-containing transcription factors are induced during the resistance response. We also identified 4 Zinc-finger type transcription factors that are induced during the resistance response. Zinc-finger type transcription factors are shown to be involved in variety of functions from plant development to senescence. It is interesting to note that we have identified a homolog of zinc-finger protein encoding LSD1 that is induced during the resistance response. LSDI acts as a negative regulator of hypersensitive induced plant cell death in Arabidopsis. Other classes of transcription factors that are differentially modulated during the resistance response include homeodomain-leucine zipper, myb-like, helix-loop-helix and chloroplast- associated transcription factors.

[0069] Unknown and Novel genes: Approximately 19% of the disease resistance response genes identified in this study appeared to have unknown functions. Most likely these genes are plant defense-specific genes. Interestingly, a class of genes that contribute to almost 6% of the resistance response genes has no homology to any translated protein or DNA sequence in the public database (thus classified as novel genes).

[0070] Conclusions

[0071] We have described the discovery of differentially modulated cDNA fragments associated with defense response in tomato by transcription profiling of the genome in resistant and susceptible genotypes treated with the pathogen, Pseudomonas syringae pathovar tomato [strain T1(A)]. We have described the identification of genes that are up or down regulated in the defense response that are specific to the response involving the interaction of Avr-Pto with Pto, and\or Prf. We have described the functional role classifications of these genes and discussed relevant genes in the context of their involvement in the defense response pathways. Our procedure for gene silencing, either in the resistant plant, if the gene is up-regulated or the susceptible plant, if the gene is down regulated, is provided. These results provide targets for inducing the defense response in tomato and other plants and markers for aiding in the identification and selection of resistant or susceptible lines in breeding strategies.

[0072] For example, the genes jasmonic acid regulatory protein (SEQ ID No: 1) and 12-oxo-phytodienoate reductase (SEQ ID No: 3) have been implicated to regulate jasmonic acid biosynthesis, which in turn induces a defense response. The gene trans-cinnamate 4-monooxygenase 4-hydroxylase (SEQ ID No: 2 and SEQ ID No: 4) is involved in synthesis of secondary metabolites, which have implicated to be associated with defense response. Further, our profiling experiments clearly show that the aquaporin gene (SEQ ID No: 5) clearly is down-regulated in the defense response.

[0073] It will be apparent to those skilled in the art that the polynucleotides of the present invention are useful for creating plants that are resistant to plant pathogens by numerous methods that are well known in the art. In one example, a polynucleotide of the present invention is linked to a pathogen-inducible promoter and a plant is transformed with the construct, such that the plant expresses the polynucleotide sequence upon challenge by a plant pathogen, thereby imparting improved resistance to the plant. In an alternative example, the promoter used is a constitutive promoter. Suitable promoters are numerous and are well known in the art. In yet another alternative example, conventional breeding methods are used to select for a plant having increased expression of a polynucleotide sequence of the invention. The present invention is suitable for the production of pathogen resistant plants from a wide variety of species, including, but not limited to: rice, wheat, barley, rye, cotton, sunflower, peanut, corn, potato, sweet potato, bean, pea, chicory, lettuce, endive, cabbage, cauliflower, broccoli, turnip, radish, spinach, onion, garlic, eggplant, pepper, celery carrot, squash, pumpkin, zucchini, cucumber, apple, pear, melon, strawberry, grape, raspberry, pineapple, soybean, tobacco tomato, sorghum, sugarcane, banana, Arabidopsis thaliana, Saintpaulia, petunia, pelargonium, poinsettia, chrysanthemum, carnation, rose, and zinnia. The plants can be engineered to express the polynucleotides of the invention by any number of well known methods, which will be apparent to those skilled in the art. Further, it will be understood by those skilled in the art that the invention is not limited to tomato genes or to the exact polynucleotide sequences disclosed herein; the invention also encompasses sequences having at least 40% or more nucleotide sequence identity with those sequences expressly disclosed herein.

[0074] Accordingly, it is to be understood that the embodiments of the invention herein described are merely illustrative of the application of the principles of the invention. Reference herein to details of the illustrated embodiments is not intended to limit the scope of the claims, which themselves recite those features regarded as essential to the invention.

[0075] References

[0076] Bruce, W., Folkerts, O., Gamaat, C., Crasta, O., Roth, B., and Bowen, B. 2000. Expression profiling of the maize flavonoid pathway genes controlled by estradiol-inducible transcription factors CRC and P. Plant Cell 12:65-80

[0077] Halterman, Dennis. 1999. Characterization of the Fenthion Response in Tomato and the Identification of Genes that Encode Fen-Interacting Proteins. Ph.D. Thesis, Purdue University.

[0078] Jia Y. and G. B. Martin (1999). Rapid transcript accumulation of pathogenesis-related genes during an incompatible interaction in bacterial speck disease resistant tomato plants. Plant Molecular Biology, 40:455-465.

[0079] Jia, Y., Loh, Y. -T., Zhou, J. and G. B. Martin (1997). Alleles of Pto and Fen occur in bacterial speck-susceptible and fenthion-insensitive tomato lines and encode functional protein kinases. Plant Cell 9:61-73.

[0080] Loh, Y. -T. and G. B. Martin (1995). The disease resistance gene Pto and the fenthion sensitivity gene Fen are closely related, functional protein kinases. Proceedings of the National Academy of Sciences USA 92:4181-4184.

[0081] Martin, G. B., A. Frary, T. Wu, S. Brommonschenkel, J. Chunwongse, E. D. Earle, S. D. Tanksley (1994). A member of the Pto gene family confers sensitivity to fenthion resulting in rapid cell death. Plant Cell 6:1543-1552.

[0082] Martin, G. B., S. H. Brommonschenkel, J. Chunwongse, A. Frary, M. W. Ganal, R. Spivey, T. Wu, E. D. Earle, and S. D. Tanksley (1993). Map-based cloning of a protein kinase gene conferring disease resistance in tomato. Science 262:1432-1436.

[0083] Shimkets, R. A., Lowe, D. G., Tai, J. T., Sehl, P., Jin, H., Yang, R., Predki, P. F., Rothberg, B. E., Murtha, M. T., Roth, M. E., Shenoy, S. G., Windemuth, A., Simpson, J. W., Simons, J. F., Daley, M. P., Gold, S. A., McKenna, M. P., Hillan, K., Went, G. T., and Rothberg, J. M. (1999) Gene expression analysis by transcript profiling coupled to a gene database query. Nat Biotechnol. 17:798-803.

[0084] Tang, X. M. Xie, Y. J. Kim, J. Zhou, D. F. Klessig, G. B. Martin (1999). Overexpression of Pto activates defense responses and confers race-nonspecific resistance. Plant Cell, 11:15-29.

[0085] Tang, X., R. Frederick, D. Halterman, J. Zhou, and G. B. Martin (1996). Initiation of plant disease resistance by physical interaction of AvrPto with Pto kinase. Science 274:2060-2063.

[0086] Zhou, J., X. Tang, and G. B. Martin (1997). The Pto kinase conferring resistance to tomato bacterial speck disease interacts with proteins that bind a cis-element of pathogenesis-related genes. EMBO J. 16:3207-3218.

[0087] Zhou, J., Y. -T. Loh, and G. B. Martin (1995). The Pto kinase conferring resistance to bacterial speck disease in tomato physically interacts with and phosphorylates a second kinase, Ptil. Cell 83:925-935.

Claims

1. A genetically engineered plant, comprising: a plant engineered to express a recombinant polynucleotide or to manipulate expression of a plant gene, wherein said recombinant polynucleotide or plant gene shows a specific pattern of expression associated with the Avr-Pto mediated defense response.

2. The plant of claim 1, wherein said recombinant polynucleotide is derived from a tomato plant resistant to bacterial speck disease caused by Pseudomonas syringae pathovar tomato.

3. The genetically engineered plant of claim 1, wherein said plant is selected from the group consisting of rice, wheat, barley, rye, cotton, sunflower, peanut, corn, potato, sweet potato, bean, pea, chicory, lettuce, endive, cabbage, cauliflower, broccoli, turnip, radish, spinach, onion, garlic, eggplant, pepper, celery carrot, squash, pumpkin, zucchini, cucumber, apple, pear, melon, strawberry, grape, raspberry, pineapple, soybean, tobacco tomato, sorghum, sugarcane, and banana.

4. The genetically engineered plant of claim 1, wherein said plant is selected from the group consisting of Arabidopsis thaliana, Saintpaulia, petunia, pelargonium, poinsettia, chrysanthemum, carnation, rose, and zinnia.

5. The genetically engineered plant of claim 1, wherein said recombinant polynucleotide is selected from the group consisting of SEQ ID No: 1 through SEQ ID No: 375.

6. A genetically engineered plant, comprising a recombinant polynucleotide (i) selected from the group consisting of SEQ ID No: 1 through SEQ ID No: 375; or (ii) hybridizes, under stringency conditions comprising a hybridization medium which includes from 0.9×SSC to 5×SSC, at a temperature of 42° C., to a DNA molecule complementary to a sequence selected from the group consisting of SEQ ID No: 1 through SEQ ID No: 375; or (iii) comprises a nucleotide sequence which is complementary to the nucleic acid molecules of (i) and (ii).

7. A method of making a transgenic plant cell comprising the steps of providing a DNA molecule according to claim 6 and transforming a plant cell with the DNA molecule under conditions effective to yield transcription of the DNA molecule.

8. A method of making a transgenic plant comprising the steps of transforming a plant cell with a DNA molecule according to claim 6 under conditions effective to yield transcription of the DNA molecule and regenerating a transgenic plant from the transformed plant cell.

9. A method of imparting disease resistance to a plant comprising the steps of: a) transforming a plant cell with a DNA molecule of claim 1; and b) regenerating a transgenic plant from the transformed plant cell, wherein the transgenic plant expresses the DNA molecule under conditions effective to impart disease resistance.

10. The method according to claim 9, wherein said recombinant polynucleotide or plant gene shows a specific pattern of expression associated with the Avr-Pto mediated defense response.

11. The method according to claim 9, wherein said under conditions effective to impart disease resistance to the treated plant.

12. The method according to claim 11, wherein said plant is selected from the group consisting of rice, wheat, barley, rye, cotton, sunflower, peanut, corn, potato, sweet potato, bean, pea, chicory, lettuce, endive, cabbage, cauliflower, broccoli, turnip, radish, spinach, onion, garlic, eggplant, pepper, celery carrot, squash, pumpkin, zucchini, cucumber, apple, pear, melon, strawberry, grape, raspberry, pineapple, soybean, tobacco tomato, sorghum, sugarcane, and banana.

13. The method according to claim 11, wherein said plant is selected from the group consisting of Arabidopsis thaliana, Saintpaulia, petunia, pelargonium, poinsettia, chrysanthemum, carnation, rose, and zinnia.

14. The method according to claim 11, wherein said recombinant polynucleotide is selected from the group consisting of SEQ ID No: 1 through SEQ ID No: 375.