PROCEDURES AND MATERIALS FOR CONFERRING DISEASE RESISTANCE IN PLANTS

Abstract: The present invention provides nucleic acids encoding polypeptides which confer resistance to Xanthomonas spp. The nucleic acids can be used to produce transgenic plants resistant to the pathogen.

Description: PROCEDURES AND MATERIALS FOR CONFERRING DISEASE RESISTANCE IN PLANTS This is a continuation in part of copending U.S. patent application No. 08/567,375, filed December 4, 1995, which is a continuation in part of U.S. provisional patent application No., 60/004,645. It is also a continuation in part of copending U.S. patent application No. 08/475,891, filed June 7, 1995, which is a continuation in part of copending U.S. patent application No. 08/373,374, filed January 17, 1995. These applications are incorporated herein by reference. Field Of The Invention The present invention relates generally to plant molecular biology. In particular, it relates to nucleic acids and methods for conferring disease resistance in plants. Statement as to Rights to Inventions Made Under Federally Sponsored Research and Development This invention was made with Government support under Grant No. GM47907, awarded by the National Institutes of Health and Grant No. 9300834, awarded by the United States Department of Agriculture. The Government has certain rights in this invention. BACKGROUND OF THE INVENTION Loci conferring disease resistance have been identified in many plant species. Genetic analysis of many plant-pathogen interactions has demonstrated that plants contain loci that confer resistance against specific races of a pathogen containing a complementary avirulence gene. Molecular characterization of these genes should provide means for conferring disease resistance to a wide variety of crop plants. Those plant resistance genes that have been characterized at the molecular level fall into four classes. One gene, Hml in corn, encodes a reductase and is effective against the fungal pathogen Cochliobolus carbonum (Johal et al. Science 258:985-987 (1992)). In tomato, the Pto gene confers resistance against Pseudomonas syringae that express the avrPto avirulence gene (Martin et al. Science 262:1432 (1993)). The predicted Pto gene encodes a serine threonine protein kinase. The tomato Cf-9 gene confers resistance to races of the fungus Cladosporium fulvum that carry the avirulence gene Avr9 (Jones et al. Science 266:789- 793 (1994). The tomato Cf-9 gene encodes a putatitive extracellular LRR protein. Finally, the RPS2 gene of Arabidopsis ihaliana confers resistance to P. syringae that express the avrRpt2 avirulence gene (Bent et al. Science 265: 1856-1860 (1994)). RPs2 encodes a protein with an LRR motif and a P- loop motif. Bacterial blight disease caused by Xanthomonas spp. infects virtually all crop plants and leads to extensive crop losses worldwide. Bacterial blight disease of rice (Oryza sativa), caused by Xanthomonas oryzae pv. oryzae (Xoo), is an important disease of this crop. Races of Xoo that induce resistant or susceptible reactions on rice cultivars with distinct resistance (Xa) genes have been identified. One source of resistance (Xa21) had been identified in the wild species Oryza longistaminata (Khush et al. in Proceedings of the International Workshop on Bacterial Blight of Rice. (International Rice Research Institute, 1989) and Ikeda et al. Jpn J. Breed 40 (Suppl. l):280-281 (1990)). Xa21 is a dominant resistance locus that confers resistance to all known isolates of Xoo and is the only characterized Xa gene that carries resistance to Xoo race 6. Genetic and physical analysis of the Xa21 locus has identified a number of tightly linked markers on chromosome 11 (Ronald et al. Mol. Gen. Genet. 236: 113-120 (1992)). The molecular mechanisms by which the Xa21 locus confers resistance to this pathogen were not identified, however. Considerable effort has been directed toward cloning plant genes conferring resistance to a variety of bacterial, fungal and viral diseases. Only one pest resistance gene has been cloned in monocots. Since monocot crops feed most humans and animals in the world, the identification of disease resistance genes in these plants is particularly important. The present invention addresses these and other needs. SUMMARY OF THE INVENTION The present invention provides isolated nucleic acid constructs comprising an RRK polynucleotide sequence, which hybridizes to SEQ. ID. No. 1 or to SEQ. ID. No. 3 under stringent conditions. Exemplary RRK polynucleotide sequences are Xa21 sequences which encode an Xa21 polypeptide as shown in SEQ. ID. No. 4. The RRK polynucleotides encode a protein having a leucine rich repeat motif and/or a cytoplasmic protein kinase domain. The nucleic acid constructs of the invention may further comprise a promoter operably linked to the RRK polynucleotide sequence. The promoter may be a tissue-specific promoter or a constitutive promoter. The invention also provides nucleic acid constructs comprising a promoter sequence from an RRK gene linked to a heterologous polynucleotide sequence. Exemplary heterologous polynucleotide sequences include structural genes which confer pathogen resistance on plants. The invention further provides transgenic plants comprising a recombinant expression cassette comprising a promoter from an RRK gene operably linked to a polynucleotide sequence as well as transgenic plants comprising a recombinant expression cassette comprising a plant promoter operably linked to an RRK polynucleotide sequence. Although any plant can be used in the invention, rice and tomato plants may be conveniently used. The invention further provides methods of enhancing resistance to Xanthomonas in a plant. The methods comprise introducing into the plant a recombinant expression cassette comprising a plant promoter operably linked to an RRK polynucleotide sequence. The methods may be conveniently carried out with rice or tomato plants. Definitions The term "plant" includes whole plants, plant organs (e.g., leaves, stems, roots, etc.), seeds and plant cells and progeny of same. The class of plants which can be used in the methods of the invention is generally as broad as the class of higher plants amenable to transformation techniques, including both monocotyledonous and dicotyledonous plants. A "heterologous sequence" is one that originates from a foreign species, or, if from the same species, is substantially modified from its original form. For example, a promoter operably linked to a heterologous structural gene is from a species different from that from which the structural gene was derived, or, if from the same species, one or both are substantially modified from their original form. An "RRK gene" is member of a new class of disease resistance genes which encode RRK polypeptides comprising an extracellular LRR domain, a transmembrane domain, and a cytoplasmic protein kinase domain (as shown in e.g., RLK5, Pto and Fen (Martin et al. Plant Cell 6:1543-1552 (1994)). As used herein, an LRR domain is a region of a repeated unit of about 24 residues as shown in Figure 1 and found in Cf-9 and RLK5). Using the sequences disclosed here and standard nucleic acid hybridization and/or amplification techniques, one of skill can identify members of this class of genes. For instance, a nucleic acid probe from an Xa21 gene detected polymorphisms that segregated with the blast (Pyricularia oryzae) resistance gene (Pi7) in 58 recombinant inbred lines of rice. The same probe also detected polymorphism in nearly isogenic lines carrying xa5 and XalO resistance genes. In some preferred embodiments, members of this class of disease resistance genes can be identified by their ability to be amplified by degenerate PCR primers which correpsond to the LRR and kinase domains. For instance, primers have been used to isolate homologous genes in tomato. Exemplary primers for this purpose are tcaagcaacaatttgtcaggnca a g at a c/t cc (for the LRR domain sequence GQIP) and taacagcacattgcttgatttnan g/a tcncg g/a tg (the kinase domain sequence HCDIK). An "Xa21 polynucleotide sequence" is a subsequence or full length polynucleotide sequence of an Xa21 gene, such as the rice Xa21 gene, which, when present in a transgenic plant confers resistance to Xanthomonas spp. (e.g. , X. oryzae) on the plant. Exemplary polynucleotides of the invention include the coding region of SEQ. ID. No. 3. An Xa21 polynucleotide is typically at least about 3100 nucleotides to about 6500 nucleotides in length, usually from about 4000 to about 4500 nucleotides. An "Xall polypeptide" is a gene product of an Xall polynucleotide sequence, which has the activity of Xall, i.e., the ability to confer resistance to Xanthomonas spp. Xall polypeptides, like other RRK polypeptides, are characterized by the presence of an extracellular domain comprising a region of leucine rich repeats (LRR) and/or a cytoplasmic protein kinase domain. Exemplary Xall polypeptides of the invention include SEQ. ID. No. 4. In the expression of transgenes one of skill will recognize that the inserted polynucleotide sequence need not be identical and may be "substantially identical" to a sequence of the gene from which it was derived. As explained below, these variants are specifically covered by this term. In the case where the inserted polynucleotide sequence is transcribed and translated to produce a functional RRK polypeptide, one of skill will recognize that because of codon degeneracy, a number of polynucleotide sequences will encode the same polypeptide. These variants are specifically covered by the term "RRK polynucleotide sequence". In addition, the term specifically includes those full length sequences substantially identical (determined as described below) with an RRK gene sequence and that encode proteins that retain the function of the RRK protein. Thus, in the case of rice RRK genes disclosed here, the above term includes variant polynucleotide sequences which have substantial identity with the sequences disclosed here and which encode proteins capable of conferring resistance to Xanthomonas or other plant diseases and pests on a transgenic plant comprising the sequence. Two polynucleotides or polypeptides are said to be "identical" if the sequence of nucleotides or amino acid residues, respectively, in the two sequences is the same when aligned for maximum correspondence as described below. The term "complementary to" is used herein to mean that the complementary sequence is identical to all or a portion of a reference polynucleotide sequence. Sequence comparisons between two (or more) polynucleotides or polypeptides are typically performed by comparing sequences of the two sequences over a segment or "comparison window" to identify and compare local regions of sequence similarity. The segment used for purposes of comparison may be at least about 20 contiguous positions, usually about 50 to about 200, more usually about 100 to about 150 in which a sequence may be compared to a reference sequence of the same number of contiguous positions after the two sequences are optimally aligned. Optimal alignment of sequences for comparison may be conducted by the local homology algorithm of Smith and Waterman Adv. Appl. Math. 2: 482 (1981), by the homology alignment algorithm of Needleman and Wunsch J. Mol. Biol. 48:443 (1970), by the search for similarity method of Pearson and Lipman Proc. Natl. Acad. Sci. (U.S.A.) 85: 2444 (1988), by computerized implementations of these algorithms (GAP, BESTFTT, FASTA, and TFASTA in the Wisconsin Genetics Software Package, Genetics Computer Group (GCG), 575 Science Dr., Madison, WI), or by inspection. "Percentage of sequence identity" is determined by comparing two optimally aligned sequences over a comparison window, wherein the portion of the polynucleotide sequence in the comparison window may comprise additions or deletions (i.e., gaps) as compared to the reference sequence (which does not comprise additions or deletions) for optimal alignment of the two sequences. The percentage is calculated by determining the number of positions at which the identical nucleic acid base or amino acid residue occurs in both sequences to yield the number of matched positions, dividing the number of matched positions by the total number of positions in the window of comparison and multiplying the result by 100 to yield the percentage of sequence identity. The term "substantial identity" of polynucleotide sequences means that a polynucleotide comprises a sequence that has at least 60% sequence identity, preferably at least 80%, more preferably at least 90% and most preferably at least 95%, compared to a reference sequence using the programs described above (preferably BESTFIT) using standard parameters. One of skill will recognize that these values can be appropriately adjusted to determine corresponding identity of proteins encoded by two nucleotide sequences by taking into account codon degeneracy, amino acid similarity, reading frame positioning and the like. Substantial identity of amino acid sequences for these purposes normally means sequence identity of at least 40%, preferably at least 60%, more preferably at least 90%, and most preferably at least 95%. Polypeptides which are "substantially similar" share sequences as noted above except that residue positions which are not identical may differ by conservative amino acid changes. Conservative amino acid substitutions refer to the interchangeability of residues having similar side chains. For example, a group of amino acids having aliphatic side chains is glycine, alanine, valine, leucine, and isoleucine; a group of amino acids having aliphatic-hydroxyl side chains is serine and threonine; a group of amino acids having amide-containing side chains is asparagine and glutamine; a group of amino acids having aromatic side chains is phenylalanine, tyrosine, and tryptophan; a group of amino acids having basic side chains is lysine, arginine, and histidine; and a group of amino acids having sulfur- containing side chains is cysteine and methionine. Preferred conservative amino acids substitution groups are: valine-leucine-isoleucine, phenylalanine-tyrosine, lysine-arginine, alanine-valine, and asparagine-glutamine. Another indication that nucleotide sequences are substantially identical is if two molecules hybridize to each other under appropriate conditions. Appropriate conditions can be high or low stringency and will be different in different circumstances. Generally, stringent conditions are selected to be about 5°C to about 20°C lower than the thermal melting point (Tm) for the specific sequence at a defined ionic strength and pH. The Tm is the temperature (under defined ionic strength and pH) at which 50% of the target sequence hybridizes to a perfectly matched probe. Typically, stringent wash conditions are those in which the salt concentration is about 0.02 molar at pH 7 and the temperature is at least about 60°C. However, nucleic acids which do not hybridize to each other under stringent conditions are still substantially identical if the polypeptides which they encode are substantially identical. This may occur, e.g., when a copy of a nucleic acid is created using the maximum codon degeneracy permitted by the genetic code. For Southern hybridizations, high stringency wash conditions will include at least one wash in 0.1X SSC at 65 °C. Nucleic acids of the invention can be identified from a cDNA or genomic library prepared according to standard procedures and the nucleic acids disclosed here (e.g. , SEQ. ID. Nos. 1 or 3) used as a probe. Low stringency hybridization conditions will typically include at least one wash using 2X SSC at 65 °C. The washes are preferrably followed by a subsequent wash using IX SSC at 65 °C. As used herein, a homolog of a particular RRK gene (e.g., the rice Xall gene disclosed here) is a second gene (either in the same species or in a different species) which encodes a protein having an amino acid sequence having at least 25% identity or 45% similiarity to (determined as described above) to a polypeptide sequence in the first gene product. It is believed that, in general, homologs share a common evolutionary past. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 shows a comparison of leucine rich repeat proteins. Figure 2A-F show partial restriction maps of BAC and cosmid clones containing regions that hybridized to Xα2i -specific probes. Figure 3 shows a restriction map of pB822, the most active copy. Figure 4 shows the results of assays measuring Xanthomonas resistance in transgenic plants comprising the Xall gene from the pB822 clone. Figure 5 shows the map position of TRK1. Figure 6 shows the map position of TRL1. DESCRIPTION OF THE PREFERRED EMBODIMENTS This invention relates to plant RRK genes, such as the Xall genes of rice. Nucleic acid sequences from RRK genes, in particular Xall genes, can be used to confer resistance to Xanthomonas and other pathogens in plants. The invention has use in conferring resistance in all higher plants susceptible to pathogen infection. The invention thus has use over a broad range of types of plants, including species from the genera Juglans, Fragaria, Lotus, Medicago, Onobrychis, Trifolium, Trigonella, Vigna, Citrus, Linum, Geramum, Manihot, Daucus, Arabidopsis, Brassica, Raphanus, Sinapis, Atropa, Capsicum, Datura, Hyoscyamus, Lycopersicon, Nicotiana, Solanum, Petunia, Digitalis, Majorana, Ciahorium, Helianthus, Lactuca, Bromus, Asparagus, Antirrhinum, Heterocallis, Nemesis, Pelargonium, Panieum, Pennisetum, Ranunculus, Senecio, Salpiglossis, Cucumis, Browaalia, Glycine, Pisum, Phaseolus, Lolium, Zea, Avena, Hordeum, Secale, Triricum, and, Sorghum. The Example section below, which describes the isolation and characterization of Xall genes in rice, is exemplary of a general approach for isolating Xall genes and other RRK genes. The isolated genes can then be used to construct recombinant vectors for transferring RRK gene expression to transgenic plants. Generally, the nomenclature and the laboratory procedures in recombinant DNA technology described below are those well known and commonly employed in the art. Standard techniques are used for cloning, DNA and RNA isolation, amplification and purification. Generally enzymatic reactions involving DNA ligase, DNA polymerase, restriction endonucleases and the like are performed according to the manufacturer's specifications. These techniques and various other techniques are generally performed according to Sambrook et al. , Molecular Cloning - A Laboratory Manual, Cold Spring Harbor Laboratory, Cold Spring Harbor, New York, (1989). The isolation of Xall and related RRK genes may be accomplished by a number of techniques. For instance, oligonucleotide probes based on the sequences disclosed here can be used to identify the desired gene in a cDNA or genomic DNA library. To construct genomic libraries, large segments of genomic DNA are generated by random fragmentation, e.g. using restriction endonucleases, and are ligated with vector DNA to form concatemers that can be packaged into the appropriate vector. To prepare a cDNA library, mRNA is isolated from the desired organ, such as leaf and a cDNA library which contains the RRK gene transcript is prepared from the mRNA. Alternatively, cDNA may be prepared from mRNA extracted from other tissues in which RRK genes or homologs are expressed. The cDNA or genomic library can then be screened using a probe based upon the sequence of a cloned RRK gene such as rice Xall genes disclosed here. Probes may be used to hybridize with genomic DNA or cDNA sequences to isolate homologous genes in the same or different plant species. Alternatively, the nucleic acids of interest can be amplified from nucleic acid samples using amplification techniques. For instance, polymerase chain reaction (PCR) technology to amplify the sequences of the RRK and related genes directly from genomic DNA, from cDNA, from genomic libraries or cDNA libraries. PCR and other in vitro amplification methods may also be useful, for example, to clone nucleic acid sequences that code for proteins to be expressed, to make nucleic acids to use as probes for detecting the presence of the desired mRNA in samples, for nucleic acid sequencing, or for other purposes. Appropriate primers and probes for identifying RRK sequences from plant tissues are generated from comparisons of the sequences provided herein. For a general overview of PCR see PCR Protocols: A Guide to Methods and Applications. (Innis, M, Gelfand, D., Sninsky, J. and White, T., eds.), Academic Press, San Diego (1990), incorporated herein by reference. Polynucleotides may also be synthesized by well-known techniques as described in the technical literature. See, e.g., Carruthers et al. , Cold Spring Harbor Symp. Quant. Biol. 47:411-418 (1982), and Adams et al. , J. Am. Chem. Soc. 105:661 (1983). Double stranded DNA fragments may then be obtained either by synthesizing the complementary strand and annealing the strands together under appropriate conditions, or by adding the complementary strand using DNA polymerase with an appropriate primer sequence. Isolated sequences prepared as described herein can then be used to provide RRK gene expression and therefore Xanthomonas resistance in desired plants. One of skill will recognize that the nucleic acid encoding a functional RRK protein (e.g. , SEQ. ID. Nos. 2 and 4) need not have a sequence identical to the exemplified gene disclosed here. In addition, the polypeptides encoded by the RRK genes, like other proteins, have different domains which perform different functions. Thus, the RRK gene sequences need not be full length, so long as the desired functional domain of the protein is expressed. As explained in detail below, the proteins of the invention comprise an extracellular leucine rich repeat domain, as well as an intracellular kinase domain. Modified protein chains can also be readily designed utilizing various recombinant DNA techniques well known to those skilled in the art. For example, the chains can vary from the naturally occurring sequence at the primary structure level by amino acid substitutions, additions, deletions, and the like. Modification can also include swapping domains from the proteins of the invention with related domains from other pest resistance genes. For example, the extra cellular domain (including the leucine rich repeat region) of the proteins of the invention can be replaced by that of the tomato Cf-9 gene and thus provide resistance to fungal pathogens of rice. These modifications can be used in a number of combinations to produce the final modified protein chain. To use isolated RRK sequences in the above techniques, recombinant DNA vectors suitable for transformation of plant cells are prepared. Techniques for transforming a wide variety of higher plant species are well known and described in the technical and scientific literature. See, for example, Weising et al. Ann. Rev. Genet. 22:421-477 (1988). A DNA sequence coding for the desired RRK polypeptide, for example a cDNA or a genomic sequence encoding a full length protein, will be used to construct a recombinant expression cassette which can be introduced into the desired plant. An expression cassette will typically comprise the RRK polynucleotide operably linked to transcriptional and translational initiation regulatory sequences which will direct the transcription of the sequence from the RRK gene in the intended tissues of the transformed plant. For example, a plant promoter fragment may be employed which will direct expression of the RRK in all tissues of a regenerated plant. Such promoters are referred to herein as "constitutive" promoters and are active under most environmental conditions and states of development or cell differentiation. Examples of constitutive promoters include the cauliflower mosaic virus (CaMV) 35S transcription initiation region, the 1'- or 2'- promoter derived from T-DNA of Agrobacterium tumafaciens, and other transcription initiation regions from various plant genes known to those of skill. Alternatively, the plant promoter may direct expression of the RRK gene in a specific tissue or may be otherwise under more precise environmental or developmental control. Such promoters are referred to here as "inducible" promoters. Examples of environmental conditions that may effect transcription by inducible promoters include pathogen attack, anaerobic conditions, or the presence of light. Examples of promoters under developmental control include promoters that initiate transcription only in certain tissues, such as leaves, roots, fruit, seeds, or flowers. The operation of a promoter may also vary depending on its location in the genome. Thus, an inducible promoter may become fully or partially constitutive in certain locations. The endogenous promoters from the RRK genes of the invention can be used to direct expression of the genes. These promoters can also be used to direct expression of heterologous structural genes. Thus, the promoters can be used in recombinant expression cassettes to drive expression of genes conferring resistance to any number of pathogens, including fungi, bacteria, and the like. To identify the promoters, the 5' portions of the clones described here are analyzed for sequences characteristic of promoter sequences. For instance, promoter sequence elements include the TATA box consensus sequence (TATAAT), which is usually 20 to 30 base pairs upstream of the transcription start site. In plants, further upstream from the TATA box, at positions -80 to -100, there is typically a promoter element with a series of adenines surrounding the trinucleotide G (or T) N G. J. Messing et al., in Genetic Engineering in Plants, pp. 221-227 (Kosage, Meredith and Hollaender, eds. 1983). If proper polypeptide expression is desired, a polyadenylation region at the 3 '-end of the RRK coding region should be included. The polyadenylation region can be derived from the natural gene, from a variety of other plant genes, or from T-DNA. The vector comprising the sequences from an RRK gene will typically comprise a marker gene which confers a selectable phenotype on plant cells. For example, the marker may encode biocide resistance, particularly antibiotic resistance, such as resistance to kanamycin, G418, bleomycin, hygromycin, or herbicide resistance, such as resistance to chlorosluforon or Basta. Such DNA constructs may be introduced into the genome of the desired plant host by a variety of conventional techniques. For example, the DNA construct may be introduced directly into the genomic DNA of the plant cell using techniques such as electroporation, PEG poration, particle bombardment and microinjection of plant cell protoplasts or embryogenic callus, or the DNA constructs can be introduced directly to plant tissue using ballistic methods, such as DNA particle bombardment. Alternatively, the DNA constructs may be combined with suitable T-DNA flanking regions and introduced into a conventional Agrobacterium tumefaciens host vector. The virulence functions of the Agrobacterium tumefaciens host will direct the insertion of the construct and adjacent marker into the plant cell DNA when the cell is infected by the bacteria. Transformation techniques are known in the art and well described in the scientific and patent literature. The introduction of DNA constructs using polyethylene glycol precipitation is described in Paszkowski et al. Embo J. 3:2717-2722 (1984). Electroporation techniques are described in Fromm et al. Proc. Natl. Acad. Sci. USA 82:5824 (1985). Ballistic transformation techniques are described in Klein et al. Nature 327:70-73 (1987). Using a number of approaches, cereal species such as rye (de la Pena et al. , Nature 325:274-276 (1987)), corn (Rhodes et al. , Science 240:204-207 (1988)), and rice (Shimamoto et al. , Nature 338:274-276 (1989) by electroporation; Li et al. Plant Cell Rep. 12:250-255 (1993) by ballistic techniques) can be transformed. Agrobacterium tumefaciens-meditoted transformation techniques are well described in the scientific literature. See, for example Horsch et al. Science 233:496-498 (1984), and Fraley et al. Proc. Natl. Acad. Sci. USA 80:4803 (1983). Although Agrobacterium is useful primarily in dicots, certain monocots can be transformed by Agrobacterium. For instance, Agrobacterium transformation of rice is described by Hiei et al, Plant J. 6:271-282 (1994). Transformed plant cells which are derived by any of the above transformation techniques can be cultured to regenerate a whole plant which possesses the transformed genotype and thus the desired Λ/tøf-controlled phenotype. Such regeneration techniques rely on manipulation of certain phytohormones in a tissue culture growth medium, typically relying on a biocide and/or herbicide marker which has been introduced together with the RRK nucleotide sequences. Plant regeneration from cultured protoplasts is described in Evans et al. , Protoplasts Isolation and Culture, Handbook of Plant Cell Culture, pp. 124-176, MacMillilan Publishing Company, New York, 1983; and Binding, Regeneration of Plants, Plant Protoplasts, pp. 21-73, CRC Press, Boca Raton, 1985. Regeneration can also be obtained from plant callus, explants, organs, or parts thereof. Such regeneration techniques are described generally in Klee et al. Ann. Rev. of Plant Phys. 38:467-486 (1987). The methods of die present invention are particularly useful for incorporating the RRK polynucleotides into transformed plants in ways and under circumstances which are not found naturally. In particular, the RRK polypeptides may be expressed at times or in quantities which are not characteristic of natural plants. One of skill will recognize that after the expression cassette is stably incorporated in transgenic plants and confirmed to be operable, it can be introduced into other plants by sexual crossing. Any of a number of standard breeding techniques can be used, depending upon the species to be crossed. The effect of the modification of RRK gene expression can be measured by detection of increases or decreases in mRNA levels using, for instance, Northern blots. In addition, the phenotypic effects of gene expression can be detected by measuring lesion length as in plants. Suitable assays for determining resistance are described below. The following Examples are offered by way of illustration, not limitation. Example 1 Plant genes may also be isolated using map-based cloning methods. This strategy consists of identifying DNA markers that are tightly linked to the gene or genes of interest. One requirement for the success of map-based cloning and physical analysis of large chromosomal regions is the availability of libraries containing large inserts of genomic DNA. Recently, Shizuya, H., et al. , Proc. Natl. Acad. Sci. 89, 8794-8797 (1992), described a bacterial artificial chromosome (BAC) system to clone large DNA fragments of the human genome. This system utilizes an F-factor-based vector and is capable of maintaining human genomic DNA fragments of >300 kb. DNA can be cloned with high efficiency, manipulated easily and stably maintained in E. coli. The following is a description of the use of this technique to isolate genes of the invention. Isolation of BAC and cosmid clones carrying _Xα27-related sequences BAC Clones A. MATERIALS AND METHODS Preparation of high molecular weight DNA in rice An International Rice Research Institute (IRRI) rice line, IR-BB21 carrying Xa-21 was used as the plant material. The plants were grown in the greenhouse for 3-5 weeks. Leaf tissue was harvested and washed with distilled water before grinding. High molecular weight DNA was extracted from rice tissue essentially as described by Hatano, S., et al., Plant Sciences, 83, 55-64, (1992) and Zhang, H.B., et al., Plant J. 7:175-184 (1994), with the following modifications: approximately 20 grams of leaf tissue was ground into powder using a cold mortar and pestle in liquid nitrogen. The powder was suspended by stirring in 200 ml cold nuclei-extraction (NE) buffer (1 MM spermidine, 1 mM spermine, 10 mM Na 2 EDTA, 10 mm Trizma base, 80 mM KCI, 0.5% Triton-X 100 and 0.4 M sucrose, pH 9.4). The mixture was filtered through two layers of cheesecloth into a GSA bottle and centrifuged at 1200 g at 4°C for 20 min. The supernatant was poured off and the nuclear pellet (pale green) was resuspended in 50 ml cold NE Buffer. The resuspended pellet was then filtered through an 80-micron sieve into a 50 ml tube to remove green tissue debris and then centrifuged at 1000 g for 10 min. The pellet was resuspended and centrifuged as above without passing through the 80-micron sieves. The nuclear pellet (about 5xl0 8 nuclei/ml) was resuspended in 2.5 ml of SCE buffer (1M sorbitol, O.1M NaCitrate, 60 mM EDTA, pH 7.0) and embedded in 2.5 ml 1 % low-melting-point (LMP) agarose (Ultrapure). 80 μl plugs were incubated in 25 ml ESP solution (0.5M EDTA, pH 9.3, 1 % sodium laurel sarcosine, 5 mg/ml proteinase K, Boehringer Mannheim) at 50 °C for two days with one change of the buffer. Each plug contained about 5 μg DNA. Partial digestion of high molecular weight DNA and size fraction by PFGE Agarose plugs were dialyzed twice against TE (10 mm Tris-HCI and 1 mM EDTA, pH 8.0) plus 1 mm PMSF (phenylmethyl sulphonyl fluoride) at 50°C for one h, and then equilibrated with Hindin buffer (50 mM NaCl, 10 mM Tris-HCI, 10 mM MgCl 2 and 1 mM dithiothreitol, pH 7.9) twice at room temperature for one hr. Plugs were melted at 65 °C for 15 min and kept at 37°C for 5 min before partial digestion. Five to seven units of HindDI (NEB, USA) per plug were added to the DNA solution and incubated at 37°C for 30 min. The reaction was stopped by addition of 1/10 volume of 0.5 M EDTA, pH 8.0. Partially digested DNA was immediately loaded into a 0.8% LMP agarose gel with a pipette tip cut off to an inside diameter of 2 mm and separated by PFGE (CHEF DR II system, BioRad, USA). Two different PFGE methods were used for the library construction. Firstly, the gel was subjected to electrophoresis at 15OV, using an 8 s initial and 8 s final switch time for 16 h at 14°C. The unresolved DNA (≥200 kb) was focused into a thin band. Secondly, the gel was subject to electrophoresis at 150V, ramped switching time from 60 to 90 s for 16 h at 14 °C. For both methods, the gel containing the partially digested DNA was cut and soaked in TE while the marker lanes of the gel were stained with ethidium bromide. The agarose slice containing fragments larger than 200 kb (the first PFGE method) or agarose slice containing 250-350 kb (the second method) was excised from the gel. The agarose slice was equilibrated in TE for 2 h at 4°C, placed in a 1.5 ml tube, melted at 65 °C for 10 min, digested with Gelase (Epicentre, USA) (one unit of enzyme per 100 mg agarose) and incubated at 45 °C for one hr. The DNA solution was directly used for the ligation reaction. Isolation and preparation of vector, and ligation reaction The vector, pBeloBAC II, was provided by Drs. H. Shizuya and M. Simon (California Institute of Technology, USA). This vector contains the lacz gene inserted into the vector pBAC108L. Shizuya, et al. (1992). A single colony was inoculated into 5 ml LB media containing 12.5 μg/ml chloramphenicol and grown at 37°C for 4-5 h before adding to 6 liters of LB media. The inoculum was grown for about 16 h at 37°C to an ODβoo,,,,, 1.3-1.5. The plasmid was isolated using Qiagen's plasmid maxi isolation kit (Qiagen, USA). Vector DNA was further purified by cesium chloride/ethidium bromide equilibrium centrifugation at 45,000 RPM for 60 h. The rotor was decelerated to 35,000 RPM for one hr. to allow the gradient to relax, using a fixed anger rotor 70.1 (Beckman, USA). The plasmid was digested with HindlU to completion and assayed by gel electrophoresis. Vector ends were dephosphorylated with HK phosphatase (Epicenter, USA) at 30°C for one hr., using 1 unit of the enzyme per 1 μg of vector ]DNA. The HK phosphatase was inactivated by heating at 65 °C for 30 min. The ligation was carried out in a 100 μl volume in which about 40 ng of the size-selected rice DNA (about 85 μl) was ligated to 10 ng of H n ϋl-digested vector (1 μl) molar ratio of about 10 to 1 in vector excess) with 400 units of T4 DNA ligase (NEB, USA) at 16°C overnight. Before transformation, the litigation was dialyzed against TE in an ULTRAFREE-MC filter tube (Millipore, USA) at 4°C overnight. BAC transformation Transformation of competent E. coli DΗ10B cells (GIBCOBRL, USA) was carried out by electroporation using a Cell-Porator (GIBCO-BRL, USA) at the following settings: voltage: 400; charge rate: fast; voltage booster resistance: 4,000; capacitance: 330 μ; impedance: low. Thirteen μl of competent cells were mixed with 0.5-1.0 μl of ligation solution for each electroporation. After electroporation, cells were transferred to 1 ml SOC solution (2% Bacto tryptone, 0.5% Bacto yeast extract, 10 MM NaCl, 2.5 mM KCI, 10 mM MgCl 2 , 10 mM MgSO 4 , 20 mM Glucose, pH 7.0) and incubated at 37°C with gentle shaking (90-95 RPM,) for 45 min. The cells were spread on LB plates containing chloramphenicol (12.5 μg/ml), X-gal (40 μg/ml) and IPTG (isopropylthio-jS-D-galactoside) (0.072 μg/ml). Plates were incubated at 37 β C for 24 h. White colonies containing rice DNA inserts were picked to a new LB plate for a second color screen. The BAC clones were transferred to 384-well microtiter plates (Genetix, UK) containing 60 μl of LB freezing buffer (36 mM K 2 HP0 4 , 13.2 mM KH 2 PO 4 , 1.7 mM Citrate, 0.4 MM MgSO 4 , 6.8 mM (NH 4 ) 2 SO 4 , 4.4% v/v Glycerol, 12.5 μg/ml chloramphenicol, LB) and incubated at 37 C C for 24 h. Since more than 95% of the colonies were still white on the second screen, only one screen was used in the subsequent experiments, and white colonies were directly picked to 384-well microtiter plates. The library was replicated in duplicate and stored in two different -80°C freezers. Filter preparation The BAC clones in each 384-well microtiter plate were replicated onto a Hybond N + filter (Amersham, USA). The filter was put into a plastic box containing LB/agar with 12.5 μg/ml chloramphenicol and the box was kept at 37°C overnight until the colonies were about 2-3 mm in diameter. Treatment of the filters was as described. Nizetic, D., et al., Nucl. Acids Res. 19, 182 (1990); Hoheisel, J.D., et al, Cell, 73, 109-120 (1993). Hybridization and washing conditions were the same as described in Hoheisel, et al. (1993). Probes were labeled using random primer extension. Feinberg, A.P. and Vogelstein, B., Anal. Biochem. 132, 6-13 (1983); Addendum 137, 266-267 (1984). B. RESULTS The BAC library described above of consists of 11,000 clones. The library was constructed using two different approaches. A first half of the library having 7269 BAC clones was made with one size selection using a compression zone method as described in Ramsay, M. and Wicking, C, Protocols in Human Molecular Genetics, 197-221 (1991). A second half of the library having 3731 clones was made using double size-selection of partially digested DNA. Double size-selection failed, however, to increase the average DNA insert size. Apparently, there were small DNA molecules still present in the size-selected DNA solution (only 250-350 kb DNA isolated). Subsequent experiments demonstrated that double size-selection of DNA between 350-500 kb for ligation yielded larger average insert size in BAC clones. Out of 54 random BAC clones chosen from the library, 50 clones contained rice DNA (93.0%). Some of the clones (7%) contained no inserts. The DNA insert sizes ranged between 30 - 250 kb with an average of 125 kb. High molecular weight DNA used to construct the BAC library was isolated from purified rice nuclei. Most of the chloroplasts and mitochondria were removed by low speed centrifugation (< 1000 g). The low frequency of chloroplast or mitochondrial clones found in the inventive BAC library (<O.3%) reduces the possibility of organellar/nuclear DNA co-ligation. The BAC library was used to construct a contiguous set of clones (contig) spanning the Xall locus. Two _Xfl27-linked DNA markers, RG103 (1 kb, see, Ronald, et al. Mol. Gen. Genet. 236:113-120 (1992)) and pTA818 (1.2 kb, equivalent to RAPD818 in Ronald, et al.) were used to screen the BAC library. RG103 is found in 8 copies in the .Xla27-containing line and hybridizes with 8 genomic HindlU DNA fragments in this line. All of these fragments are genetically and physically linked to the Xall disease resistance locus. pTA818 hybridizes with 2 DNA fragments and at least one of these fragments is linked to the Xall locus. Ronald, et al. (1992). 7296 BAC clones were probed-with ρTA818 (2 copies) and RG103 (8 copies). Seven and five BAC clones hybridizing with RG103 and pTA818, respectively, were identified. BAC DNA was isolated from these clones and digested with HindlU. The DNA fragments were separated by PFGE. Southern analysis showed that the 7 RG1O3 hybridizing BAC clones carried 4 different copies of the RG103 genomic HindlU fragments. The probe was hybridized with a 4.3 kb DNA fragment and 9.5 kb fragment, a 9.6 kb fragment and a 6.2 kb fragment. The size of the DNA fragments are deduced from lambda DNA digested with HindlU. Four BAC clones were isolated that carried one copy of the pTA818 HindlU fragment and one BAC clone was identified that contained the other copy. One of the pTA818 containing BACs also hybridized with the marker PTA248 (equivalent to RAPD248 in Ronald, et al. (1992), confirming that these two cloned RAPD markers are within 60 kb of each other. Ronald, et al. (1992). The identification of 12 BAC clones hybridizing with 2 cloned DNA sequences (corresponding to 10 DNA fragments in the rice genome) is slightly lower than the 20 clones expected based on screening 2x genome equivalents (7296 clones, 450,000 kb genome, 125 kb average insert size). Specifically, the pTA818 sequences and four (out of eight) of the RG103 hybridizing sequences are over represented in this portion of the library. By contrast, the other four RG103 hybridizing sequences are under represented. The DNA insert sizes of these clones ranged from 40 to 140 kb. Cosmid Clones A. MATERIALS AND METHODS Preparation of high molecular weight (HMW) DNA from rice leaves. The rice line, 1188 carrying the Xa-21 locus, was used as the plant material for isolation of HMW DNA. 120 g 4-6 weeks old leaf tissue was harvested and ground into fine powder using a cold mortar and pestle in liquid nitrogen. The powder was then suspended by stirring in 800 ml cold H buffer [4 mM spermidine, 1 mM spermine, 10 mM EDTA, 10 mM Tris-HCI, 80 mM KC1, 0.5 M sucrose, lmM PMSF (phenylmethyl sulphony fluoride, add just before use), 0.5% (v/v) Triton-X 100, 1/1000 (v/v) 3-mercaptoethanol (add just before use), pH 9.5]. The mixture was filtered through an 80-micron sieve into GSA bottles and the pellet resuspended in 400 ml H buffer and filtered again. The two filtrate volumes were combined and centrifuged at 3500 rpm for 10 min at 4°C. The pellet was resuspended in 300 ml washing buffer (same as H buffer except PMSF and /3-mercaptoethanol) and centrifuged at 3500 rpm for 10 min at 4°C. The pellet was washed two additional times until the color of the pellet was pale green. The pellet was resuspended in 40 ml washing solution and the nuclei were lysed by adding an equal volume of lysis buffer ( 2% Na laurel sarcosine, 100 mM Tris-HCI, 0.5 M EDTA, pH 9.5) containing 2 mg/ l proteinase K (Boehringer Mannheim). Proteins were removed by incubation at 50°C for 5 hr and then extraction of the solution (by gentle inversion) with an equal volume of phenol-chloroform-isoamyl alcohol (24:24:1) for 30 min at room temperature. The HMW DNA was precipitated by gently layering 1/10 vol. of 3M sodium acetate (pH 5.5), 2 vol. of ethanol and inverting several times. Finally, the DNA was removed from the ethanol using wide-mouth pipette tips, washed with 70% ethanol, dried and dissolved into 1 ml of TE (10 mM Tris-HCI, lmM EDTA, pH8.0) at 4°C overnight without shaking. Normally, 250 ug HMW DNA can be isolated from 120 g leaves. Preparation of insertion DNA (A) Partial digestion of HMW DNA Pilot experiment. 30 ug (70ul) of HMW DNA was mixed with 10 ul of 10 x Sau3AI buffer (NEB) and pre-warmed at 37°C for 5 min. 20 ul (2 units) of Sau3AI was then added to the DNA solution, gently mixed with a wide-mouth pipette tip and incubated at 37°C. 15 ul aliquots were removed at 0, 5, 10, 20, 30 and 70 min and immediately mixed with 5 ul 0.5 M EDTA (pH8.0) on ice to stop the reaction. The samples were analyzed by electrophoresis through a 0.3% agarose/TBE gel at 2 V/cm gel length for 36 hr in the cold room. Large-scale partial DNA digestion was achieved by repetition of the pilot experiment using the optimized incubation time intervals of 20 min at 37°C. (B) Size-selection The partially digested DNA was fractionated on a sucrose density gradient of 5 to 40% by centrifuge in an SW27 rotor at 26,000 rpm at 20°C for 13 hr. 0.8 ml fractions (20 total) were collected by carefully placing a capillary tube at the bottom of the centrifuge tube and pumping out the gradient at a very slow speed. 20 ul of each samples was assayed on a 0.3% agarose gel at 2 V/cm gel length for 36 hr. DNA fractions with approximately 35-50 kb were pooled together. After diluting the sucrose with an equal vol. of H2O, the DNA was precipitated with 2 vol. ethanol. The partial fill in reaction was achieved using standard protocols. Ligation, packaging and transfection The cosmid vector, pHC80, was kindly provided by Dr. Scot Hulbert. Vector and insert DNA were ligated in a 2 to 1 molar ratio, at a final concentration of 0.8 ug/ul. The ligation reaction was carried out with 600 units of T4 DNA ligase (NEB, USA) at 16°C for overnight. The ligated DNA was in vitro packaged with Gigapackϋ packaging extract (Stratagene, USA) and transfected into competent cell, E.coli NM554, according to the Stratagene manual. Library screening 61440 cosmid colonies (more than five genome equivalents) in 160 384-well microtiter plates were transferred onto Hybond N+ filters (Amersham, USA) in two type densities. In the first method, the cosmid clones were replicated in low density (1536 colonies/11.5x15 cm filter) using manual replicators (Genetix, U.K.) and grown on LB/agar with 100 ug/ml ampicillin for overnight. Forty filters were made to cover the whole cosmid library. In the second method, the cosmid clones were replicated in high density arrays using a Beckman Biomek™ robotic workstation and grown using the same method as above. Using 3 x 3 arrays, 3456 colonies were transferred onto an 8.5 x 12cm filter. In order to exactly localize the positive colonies on a negative background, a reference cosmid colony (containing the RG103 marker) was plated in the first position of each 3 x 3 grid. The remaining eight offset position were plated with colonies from eight microtiter plates of the cosmid library. In this case, 20 filters in size of 8.5 x 12 cm each can cover the whole library. For hybridizations with a unique probe, the RG103 probe was mixed with the unique probe in a ratio of 1:4 to produce the reference pattern. Bacteria on the filters were lysed and fixed using the steaming water bath procedure with the following modification: colonies were placed face up on top of two pieces of 3 MM Whatman soaked in lysis solution (0.5 M NaOH, 1.5 M NaCl) for 4 min at room temperature, the plastic boxes containing the filters were incubated in a steaming water bath at 85 °C for 6 min and then the filters were transferred to 3 MM Whatman soaked in neutralization buffer (1 M Tris-HCI (pH7.4), 1.5 M NaCl) for 4 min. Proteins and cell debris were removed by submergence in 50 ml proteinase K solution (50 mM Tris-HCI (pH8.5), 50 mM EDTA (pH8.0), 100 mM NaCl, 1 % (w/v) Na-lauryl-sarcosine, 250 ug/ml proteinase K) and incubated at 37°C for 20 min. The filters were gently washed in 2 X SSC solution for 5 min at room temperature, dried and UV treated the filters at 10 cm for 2.5 min. Hybridization was performed according to standard procedures as follows: filters were subjected to prehybridization solution (7% SDS, 0.5 M Na 2 PO 4 (pH 7.2), 1 mM EDTA, 100 ug/ml ssDNA) at 65°C for 2 hr to overnight. Probes were labeled using the random primer extension procedure and hybridization was performed at 65 °C with shaking overnight. The filters were washed briefly in (40 mM Na 2 PO 4 (pH 7.2), 0.1 % SDS) at room temperature and the filters were incubated in the same solution at 65 °C for 20 min with gentle shaking. B. RESULTS Three Xα27-linked markers (RG103, RAPD 248 and RAPD 818) were used to screen the cosmid library. Genomic Southern analysis showed that the copy numbers of these three markers in resistant lines are 8, 1 and 2 respectively (unpublished results). Six positive cosmid clones hybridizing with the RG103 marker were identified and confirmed by further Southern analysis. However, no positive clones were identified to contain RAPD248 and RAPD818. Example 2 Characterization of the Xall genes Five cosmid clones and 1 BAC clone isolated in Example 1 were further characterized by restriction enzyme mapping. Figures 2A-2E are partial restriction maps of the cosmid clones. Figure 2F is a partial restriction map of the BAC clone. An open reading frame in one of the clones, pB806, was identified (SEQ. ID. No. 1). It includes the promoter region, the predicted intron and a partial 3' sequence. SEQ. ID. No. 2 shows the predicted amino acid sequence. The predicted intron has been spliced out. The predicted amino acid sequence has revealed two features of the protein which indicate it is encoded by a member of the new class of plant disease resistance genes referred to here as RRK genes. First, the extracellular domain of the proteins encoded by these genes comprise a block of about 23 tandem leucine-rich repeats (LRR) with an average length of 24 amino acids. The LRR motif has been implicated in protein-protein interactions and ligand binding in a variety of proteins. The extracellular domain also comprises a region between the LRRs and the signal peptide which contain a motif, SWNTS, which is conserved among a number of proteins, including, Cf-9, PGIP, and RLK5. In addition, the protein comprises a region with high sequence identity to receptor-like protein kinases (RLPKs) such as RLK5 and TMK1 (Walker et al. Plant J. 3:451 (1993); Chang et al. Plant Cell 4: 1263 (1992); Valon et al. Plant Molec. Biol. 23:415 (1993)) as well as the tomato resistance gene product, Pto (Martin et al. Science 262: 1432 (1993). The signal domain, the extracellular domain (including the LRR region), the transmembrane domain and the cytoplasmic kinase domain are identified in SEQ. ID. No. 2. Figure 3 is a restriction map of a second clone, pB822, which was used to construct the plasmid used in the transformation experiments described in Example 3, below. The Xall gene in this clone has also been sequenced (SEQ. ID. No. 3). The predicted amino acid sequence (SEQ. ID. No. 4) revealed the same motifs identified in SEQ. ID. No. 2. The protein kinase domain carries 11 subdomains containing 15 conserved residues diagnostic of protein kinases and is flanked by a 31 aa juxtamembrane domain (aa 677-707) and a C terminus domain. The presumed intron is located between the two highly conserved residues P and E (aa 892 and aa 893) in the putative catalytic domain. The consensus sequences present in subdomains VI (DIKSSN) and Vm (GTIGYAAPE) strongly suggest that Xa-21 has serine/threonine kinase (as opposed to tyrosine) activity. Previous work has demonstrated that phosphorylated RLK5 protein interacts with the kinase interacting domain (KID) of a type 2C serine-threonine protein phosphatase (Stone et al , Science 266:793-795 (1994)). The KID binds the phosphorylated LRR containing proteins, RLK5 and TMK1, but fails to bind the S-related receptor kinases ZmpKl and RLK4. These results suggests that the Arabidopsis KID is functionally analogous to the SH2 domain of animal proteins. Sequence alignment of the Arabidopsis receptor like kinases RLK5, TMK1 with Xa-21 reveals a set of conserved amino acids (N/Q)X(L/V)S(G/S)(L/A)(F/V)(P/E) surrounding a serine residue that is carboxy terminal to the last residue (arginine) highly conserved in all protein kinases (position 999 in Xa21 gene product). The carboxyl terminal position of this consensus in these proteins is similar to the carboxyl terminal phosphotyrosine of the Rous sarcoma virus oncogene product pp60 c-Src which is essential for binding to SH2 domain containing proteins. These conserved amino acids are lacking in the S related receptor kinases ZmpKl, RLK4 and SRK6 and in intracellular kinases which do not bind KID. Thus, this region act as a high affinity and specific binding site for proteins containing KID. Modification of the amino acid sequence of this region of Xall can thus be used to alter affinity for the KID protein and thus control intracellular signalling in response to ligand binding of the LRR domain. Example 3 Plant transformation using an Xall gene The Xall gene described above was used to transform rice plants to demonstrate that the genes could confer Xanthomonas resistance to susceptible plants. The gene was introduced into susceptible rice strains using a variation of the methods of Li et al , Plant Cell Rep. 12:250-255 (1993). Briefly, co-transformation was carried out using the hygromycin construct pMON410 (from Monsanto) and a bluescript vector containing the sequences of interest. In addition, the Kpn fragment of pB822 was cloned into the pTA818 vector, which is derived from Invitrogen vector per 1000 and contains the lkb fragment RAPD818 (Ronald et al , supra). The resulting plasmid is referred to as pC822. The plants were selected on hygromycin (30mg/L) and then screened for resistance to Xoo race 6. Standard methods were used to test Xanthomonas resistance in the transformants. The assays were carried out according to the methods of Kaufman et al Plant Disease Rep. 57:537-541 (1973). Briefly, Xoo race 6 was grown on PSA plates for 3 days. The bacteria were scraped up, resuspended in water and the OD adjusted to 10 9 colony forming units per ml. Scissors were dipped in the suspension and leaves from the transformed plants (4 months post bombardment) were cut 5 cm from the tip. Plants were scored for the presence of lesions 11 days post inoculation. Figure 4 shows lesion length data from experiments using an expression vector comprising the gene from the pC822 clone. Individuals derived from independent transformants 106, -9, -22, -11, -17, -1, -12, -4, 16, and -29 carry the pC822 construct and showed increased resistance as compared to susceptible untransformed controls (IR24), as well as rice plants transformed with the vector (1-15). Example 4 Isolation of RRK genes from Tomato As noted above the Xa21 sequence can be used to isolate RRK genes from other plant species using a degenerate primer or low stringency hybridization approach. This example describes the isolation and characterization of two RRK genes from tomato using a degenerate primer approach. Degenerate primers were prepared so that the PCR (polymerase Chain Reaction) products should amplify between the LRR and kinase domains and therefore span the transmembrane domain. The forward primers were taken from motifs conserved in the LRR region of Xa21 and several other plant proteins (e.g. , Cf-9, RLK5, and PG1P). The reverse primers were taken from motifs conserved in the Xa21 kinase domain and other plant serine-threonine kinase domains( e.g., RLK5, Pto, and Fen (Martin et al. Plant Cell 6: 1543-1552 (1994)). The degenerate primers used for amplification of PCR products were as follows: 1. LRR region TCA AGC AAC AAT TTG TCA GGN CA(A/G) AT(A/C/T) CC (SEQ. ID.No. 5) 2. Kinase region TAA CAG CAC ATT GCT TGA TTT NAN (G/A)TC NCG (G/A)TG (SEQ.ID. No. 6) TAA CAG CAC ATT GCT TGA TTT NAN (G/A)TC (G/A)CA (G/A)TG (SEQ. ID. No. 7). TAA CAG CAC ATT GCT TGA TTT NAN (G/A)TC (T/C)CT (G/A)TG (SEQ. ID. No. 8) The PCR The PCR conditions were as follows (20 micro liter reaction): First cycle: 94C for 30sec (denaturing) 55C for 30sec (annealing) 72C for lmn (extension) For the next 19 cycles, the annealing temperature dropped down 1C every cycle. After the 20 cycles are finished, the reaction was incubated for 10 min at 72C . After the initial amplification using these degenerate primers, a second round of amplification was performed with the following specific primers: TAAGCAACAATTTG (SEQ. ID. No. 9) and TAACAGCACATTGCTTGA (SEQ. ID. No. 10) The conditions for this amplification was as follows: 35 cycles 94C for 15sec 55C for 15sec 72C for 15sec At the end of the 35 cycles, the reaction was incubated for 72C for lOmin The PCR products were cloned and used as probes to a tomato cDNA library. The library was constructed from tomato cDNA thatwas primed with oligo DT primers, ligated to EcoRI adaptors and cloned into a lambda GT11 vector. These primers were used to isolate two tomato PCR products and cDNAs belonging to the RRK family of disease resistance genes. The first clone TRKl (Tomato Receptor Kinase 1) is a 250bp PCR product and was used to isolate partial cDNAs. The DNA sequence is shown in SEQ. ID. No. 11. The deduced amino acid sequence of TRKl is shown in SEQ. ID. No. 12. This clone is present as one or two copies in the tomato genome and onecopy maps to the short arm of chromosome 1 in the proximity of a resistance gene to Xanthomonas campestris pv. vesicatoria (Rxl) (Zu et al. Genetics 141:675-682 (1995)) (see, Figure 5). The second clone TRLl (Tomato Receptor Like 1) is a 496bp PCRproduct. The DNA sequence is shown in SEQ. ID. No. 13. The deduced amino acid sequence is SEQ. ID. No. 14. TRLl maps within a few cM of men (see, Figure 6) a mutation on chromosome 3 that causes spotty necrosis on plants, typical of a defense phenotype. These results indicate that the Xa21 gene can beused to isolate RRK genes from other plant species. For example, the TRKl and TRLl genes that were isolated are important components of plant signal transduction pathways leading to a defense response. These genes are useful to engineer disease resistance in tomato and other plant species. The above examples are provided to illustrate the invention but not to limit its scope. Other variants of the invention will be readily apparent to one of ordinary skill in the art and are encompassed by the appended claims. All publications, patents, and patent applications cited herein are hereby incorporated by reference. SEQ. ID. No.1 RRK-F aagcr t tctaaatra r-taactcraagrcrgrrarrarcccsaag-cacarcatcatcatac ataaratr-rratarrcacgacarccrraagcraaatgcrr-rtggccafcctcrtatcrrtt taaaσaaat"rsrcϊ=ccaarraagarσagagτgτcrtcraσcaa«"--gccagrϊτ.t » acaa tg t crrtgagtccrcacacartrtcargatgr-caccaaraaatracggacgccgrgtttag ttc aaagrtt tcrtcaaacrracaacrtiircaatcgcarcaaaactti'εcrccracacac acaaacrtrcaactrttccarcacatcσrrccaatrtcaaccaaacrtccaattrtggrat gaacraaacaeagceaaaaacaaaarergrgt.gt.tatggc g crgxrragatteraacrrtt ccatracarcaaacrtrccracaracacσaacrt caacrrrtccgrcacarcgr'εtcaat ttftraaaacrrccarrrttaacgrggaacraaacacaaccrararaacggaatfsgtcaa aaacrcaarggrgaaagrcacaccccacaggaaσggcgcgcrcεagrcaagaca-ccar-caa acaggracacaggrrgracragcrtgrcargr ratcrtgcgrctgcgagacgraaarcca tgceaaacaaaagrgcrrcraragagaratcataaggatarggrtrggggccararccaac tgctcaggagagarctcgrrcggaggrgaggrragargtrcacctcrccacacataacgaa ggcgarerrcrrcgcara gar aggca-ctagaraaaataaccrtaaaaaataaatcaara tgatrrt-'rtagaaaaaaarTzraracacraagtaraaσcatrgrcaaggaggaaσaaaca cacacrczcatatagaσagaraσaaacaragcraraσgraσrgrcacrgagrarrtrccat cacgcatacccataraaaatragggggrgrracarccaraggrgraaagrtttggcatgrr aratcgagrartacgraqaatgccgtarraggrgrccgggcacraacaaaaaaaraarrac agaarcsgrtagtaaaccgcgagataaarrεattaagccraacraatcceatcatraacaa atgr racc ragcaccacarrgrcaaarcatggagcaatraggtrtiaaaagatrcgrcrc gcaaat agtcataatcrgrgcaarragr-πatrrtragacratatttaagacr-cgracag grgrr aaacgτ-cgacgrgacarggrgcaaaarrrtagggegtt-carcragacacrcscrr aatragaaaσrraggaaσaggcggraaagaacgcagcatgacrgaaacrttgaaaarrtga taaggracaccaacrggagrarcr-trarrttcartgaaσacrrtgaccagaaσagcr ga cccgrtrrrcrrggag'cagccagcaa'cgτttca'C'ccrr'crccrtttgcrgggacttcrtrt tattttttttgacaggagccattrgc gggacfcgggatcccrrtactgtrataggaccag tgcrtqaarcraaacacrgcarrgatcagcrcagcrcar gragcgcactccrccgcargc ATGGCC^GΛTCACC ACGTCGCΤCATGATCTCTT TTTGCTGCTGCTCCTCTTGATCGGCC CAGCGAGCAGTGACGATGATGCTGCTGCTCCTGCTGCTCGTACCAGTACAGGCCGCGTCCC GGCGACGAACTCGCGCTGCTCTCTT CAAGTCATCCCTGCTACACCAGGGGGGCTTGTACG CTGGCATCTTGGAACACGTCCGGCCACGGCCAGCACTGCACATGGG7GGGTGTTGTGTGCG GCCGCCCGCGCCCG ACCCACACAGGGTGGTGAAGCTG RGCTGCGCTCGTCCAACCTGTC CGGGATCATCTCGCCGTCGCTGGGCAACCTGTCCTTCCTCAGGGAGCTGGACCTCAGCGAC AΛCTACCTCTCCGGCGAGATACC-ACCGGAGCTCAGCCGTCTAGCAGGCTTCAGCTGCTGG AFICTGAGCGGTAACTCCATCCAAGGGAGCATCCACGCGGCCΛTTGGAGCATGCACCAAGTT GJU-ATCCCTAGACCTCAGCCΛC_JΛCCAACTGAGATTGGΤGCC^^ TTTGTACCT CACJICΑULTGGTTATGTCAGIGΛGAGATTCCATCTGATTTTGGGCAATCTCA C ACGCCTTCAGTATT GATTTGACCTGCAACAGATTATCACGGAG ΓATACCTTCATCGC TΛGGGCAGC7 AGCAGC_AG7C7ATTGACTATGAATTTTGTG TACGAΛCAATC7AACTGGC ATGATCCC-_^UITTCTATCΎGGAAC TTTCGTCTCTAGCAGCGTΎ AGCTGΎCAAGCGAAAA ACAAGCTAGGTCGTATGATCCCTACAAATGCATTCAAAACCCTTCACCTCC CGAGGTGGT AGATATGGG ACTAACCGATTCCATGGCAAΛATCCCTGCCTCAGTTGC AATGCTT TCAT CTGACACGGCTTCAGATTGATGGCAACTTGTTCAGTGGAATTATCACCTCGGGGTTTGGAA A > T_AT7GGGGGTTCATT7CTGACC7AACAAATTGCTCCAAATTACAAACATTGGACT7GGGA GJU U^TAACCTGGGCGGAGTTCTTCCTAATTCGTTTTCAVATCTTTCCACT CGCTTAGTT TTCTT^CACTTGATTTGAATAAGATCACAGGAAGCΛTTCCAAAGGATATTGGCAATCTTAT T C ^ITTACAACATCTCTATCTCTGCAACAACAATTTCAGAGGGTCACTTCCATCATCGTTG Sea. ..-. 1 ::r.c:r.ueo VΛ **—Λ<-rt-r. m mAGAAAC77AGGCA7777AG7CGCZ7ACGAAAACAAC77GAGCGG77CGATCC CATTGGCZATAGGAAAT TTACTGAAC77AATAT2TTACTGCTCGGCACCAACAAAT7CAG TGG77GGA7ACCA7ACACAC7C7 AAACC7CACAAAC77G77G7CA77AGGCC7C7CGCAC C7CGCACCACAA7CAGGG77GGA7AC 7ACACA7C7ZAACC77ACAAC7S7G7CATAGCC7 7CAC7A7ACC7AG7GGG7CCCAAA7ACZCGAGG7GAAA77AA77CAAA7AG7CCAAACACC TA7CAAAAAGA7GA7CAA7G7A7CAAAAAA7ACAC77GGAGGGA7CAGA7ACCGACAAGAA A7AGGGCA7C7GAAAAA7C7AG7AGAA77CA7GCAGAA7CGAA7AGA7A7CAG7AAAATCC CTAACACGC77GG7GA77GCCAGC7r77ACGG7A7C7TTA7C7GCAAAA7AA7TTSTTATC TGG7AGCA7CGCA7CAGCC77GGG7CAGC7GAAAGG7C7CGAAAC7777GA7C7CTCAAGC C7CGA7G77G7CCGA77AC7AGAGAACAGAAAGCA777T CAGC7C7ACC7A7777C7T7 C7C7GG7CGCAGCAC7GGCCA7 C777CA7CAC777AC77G 77A7AACC7GGAACAAGAG AAC7AAAAAGGGAGC Z 77CAAGAAC7777A7GAAAGG CACC A77GG7C7r77A7CCG Λu _. _. VJ J inAΛΛU nA nw 4 VJU . _. «.. -.-_k.«.un.t_-r_-rk_. __ . -i._..ιvιu_ _._. -luni Λi * __ u • uftnυv.n_...-_ unr_nιni u^un n^ uvr__. _._.._- <_ i__nnun_,ntj * -. A I __ - -. J -»JAUC CC7GAACC7G77C7ACAC7G7GA7G77AAA7CAAGCAA7G7CC7G77AGA7777GA7A7GG 7AGCGCA7G77GGAGA77C7GGGC77GCAAGAA7AG77G77GA7GGGACC7CA77GA7ACA ACAG7CAACAAGC7CGA7GGGA777AGAGGGACAA77GG 7A7GCAGCACGAggccagcaa grccrrccagrarr^rgcarrrrczgarcrcragrgs-rarargaaacagrrrrracc cta gtgaaacrqarggagaararaagcaarraarrgaacraarraaar gcacaaaaacaagac tattrgccatarcrarTcagargcraaararagcragrtcaragaggracararfrεt rt ataraggaarcragagcracracacacrraaarcaaatrargggrgrtrrcrgcrcracac tgcaarargaaacgarrarcaqaaqgarcaaarrrgagraaar rgrcaarrrracarrra agaaacaci'Errr'rrtgrarcracragrrarracaarrrrrrartrcaagaacr'cgcattg accarαaaaaqracr ggtacracrtcraarrcrcacarggaggrggrgaaaataatatag atacaaaaacgaaαratcatargrrgrg-cgaratacraraarczcaargaacacaaacagg arccgracaaaagraatrggccatcatagcaacrgatrgcr-zggggraacrgraragcaca arcacaccaaarrrcrrragacargrarrrgraaarragarrcr aaagrtaaacacgaaa tttcatrggrarrrargrrr rrrataraaraaaaarraarccaaccr-rtacarcraccat ttgcccagccatc-rtrgtrarrtgrgaratrraacacgraarrtracataar'catacatec aagrr rrrrrattraacacr 3 gaaatrrgaaarcgrarrrccracrcaaacaGAG7A7GG CG7CGGG ACA77GCA7CAACACA7GGAGATA77TACAGC7ATGGAATTC7AG7G TGGAA ATAG7AACCGGGAAGCGGCCAAC7GACAG7ACA7T AGACCCGA777GGGCC7CCG7CAG7 ACG77GAAC7GGGCC7ACA7GGCAGAG7GACGGA7G7TG77GACACGAAGC7CA7TTTGGA TTC7GAGAAC7GGC7GAACAG7ACAAA7AATrC7CC__A7G7AGAAGAA7CAC7GAA7GCAT7 GT77CGC7GC77AGAC77GGG77G7G77GC7C7CAGGA77TNCCA77GAG7AGACGCCACC CGGAGA7A7CACCGACGAAC7GAatgccarcaaacagaarc-r rccggagrrgrrtccagt g grgaaggrgcgagcctsgaacrcrgatgrtargrcrtgraargrrrtarrgccacragr ctrcagarrggaargcrcrtccgarcagactrcrtcagrggratcraccacacgarcacta aagrcarcgrggcrarrrccrgatccagcararcrgatcatgcargrrcrgrgrrϊtatac crgrarr tacrcrgaarrgccacaccrcaacccrgccϊctgrttgr'csggcaracaaaag atagrga gagrararrgrttcaggggcrrrcragrrggcgrg-ccrcgcttaccggcacgca cgcaqcccgagggrggg-crtcrrrrrti ' srrccatrg'crartccg'crgcrtttrrccaccac ggraqat trrt " s rt 3 gga -cca f -r =cg "sgr"s tc 3 a gc argcrg SEQ. ID. No. 3 ORF 3918 [3075 bp interupted by one intron ( 843 bp) ] ATGATATCACTCCCATTATTG CTC TCGTCCTGTTGTTCTCTC CG CTG CTGCTCTG CCCTTCAAGCAGTGACO ATGGTGATGCTGCCGGCGACGAACTCGCGCTGCTCT-^ TCAAGTCATCCCTGCTATACCAGGGGGGCCAGTC GGCA7CTTGGAACACGTCCGGCCACGGCCAGCACTGCACATGGGTGGGTGTTGTGTGCGGCCGCCCCCCCCGC CACCCACACΛGGGTGGTGAAGCΤCCTGCTGCCCΤCC CCAACCTGTCCGGΒATCATCTCGCCGTCGCTCGGCA TGTCCTTCCTCAGGGAGCTGGACCT-CGGCGA ΥVCTACCTCTCCGGCGAGATACCACCGGAGCTCAGCCGTCT CAGGCTRCAG-_RRGCTGGAGCTGAGCGATAACTCCATCC_^GGGAGCATCCCCGCGGCCARRGGAGCATGCACC TTGAC_ATCGCTAGACCTCAGCCAC__AACCAACTGCGAGCTATCATCCCACGTGAGATTCGTGCCACCTTGAAAC TCTOGAATTTGTACCTTTACAAAAATGGTTTCTCAGGAGAGATTCCATCCGCTTTGGGCAATCTCACTAGCCT GGACTTTGATTTGAGCTTC_AAC»GATTATCAGGAGCTATACCRRTCATCACTGCXWCAGCTCAGCAGTCTATTC ATGAATTTGGGACAGAACAATCTAAGTGGGATGATCCCΑUVTTCRATCTGGAACCTTTCGTCTCTAAΒAGCCT GTGTCAGAGAAAACAAGCTAGGTGGTATGATCCCTACAAATGCAT CAAAACCCTTCACCTCCTCGAGGTGAT TATGGGCACTAACCXITTTCCATGGCAAAATCCCTGCCTCAGTTGCTAATGCTTCTCATTTGACAGTGATTCAΒ TATGGCAACTTGTTCAGTGGAATTATCACCTCGGGGTTTCGAAGGTTAAGAAATCTCACAGAACTGTATCTCT GAAATTTGTTTCAAACTAGAGAACAAGATGATTGGGGGTTCATTTCTGACCTAACAAATTGCTCCAAATTACA ATTGAACTΥGCGAGAAAATAACCTGGGGGGAGTTCTTCCTAATTCCTTTTCCAATCT7TCCACTTCCCTTAG'L" CTTGCACTTGAATTGAATAAGATCACAGGAAGCATTCCGAAGGATATTGGCAATCTTATTGCCTTACAACATC ATCT-TTCCAAAUVCAATTTAGAGGGTCTCRRCCATCATCCTTGGGCAGGCTTAAAAACTTAGGCATTCTACT CTACGAAAACAACTTGAGCGGTTCGATCCCCTTGGCCATAGGAAATCTΓACTCAACTTAATATCTTACTGCTC ACCAACLAAATTCAGTGGTTGGATACCATACACACTCTCAAACC CACAAACTTCTTGTCATTAGGCCTTTCAA ATAACCTTAGTGGTCCAATACCCACTGAATTATTCAATATTCAAACACTATCAATAATGATCAATGTATCAAA TAACTTGGAGGGATCAATACCACAAGAAATAGGGCATCTCAAAAATCTAGTAGAATTTCATGCAGAATCGAAT TTATCΑGGTAAAATCCCTAACACCCTTGGTCATTGCCAGCTCTTACGGTATCTTTATCTGCAAAATAATTTGT CTCGTAGCATCCCATCAGCCRTGGGTCAGCTGAAAGGTCTCGAAACT TTGATC CTCAAGCAACAATTTCTC CCAGATACCCACATCCT AGCAGATATTACTATGCTTCATTCCTTGAACCTTTCTT^ CTCCCAACCATTCGTCCT-ΓTCCCACCTCCATCCCGGATCTCAATCCAAGCCAATGCCAAACTCTGTCGTGCAA TCTGCCCCCAGCACTGCCCATCCTCTCATCACTCTACTTGCTTATAACCTGGCACAAGAGAACTAAAAAGGCA CCRRCAAGAACT CCATCAAAGGCCACCCATTGGTCTCTTATTCCCAGTTCGTAAAAGCAACAGATGGTT CG CCAC-__AATTTCTTGGGTTCTGGATCATTTCGCTCAGTATACAAAGGAAAGCTTAATATCCAAGAT»TCTTGC GAAGGTACTAAAGCΓTCAAAATCCTAAGGCGCTCAAGAGTTTCACTCCCGAATGTGAAGCACTACGAAATATG CΛ7CGAAATCT7CTCAAGATAG7TACAAT7TCCTCGAGCATTGATAACACAGGGAACCATTTCAAAGCAATTG ATGACRRCATCCCC-AACGGCAGTCTCGAAGATTCGATACACCCTGAAACAAATGATCAAGCAGACCAGAGCCA GAATCTCCATCGAAGACTCACCATACTACTTGATCTTCCCTCCGCACTGGACTATCTTCACCCCCATGGCCCT CCTCTTCTACACTCTGATATTAAATCAAGCAATCTGCTCTTAGATTCTGATATCCTAGCCCATCTTCGAGATT GGCTTCCAAGAATA I GTTGATGGGACC CATTCATAAUVCAGTCAACAAGCTCGATGGGATTTATAGGGAC TGGCTATCCAGCACCAGGTCAGCAAGTCCTTCCACTATTTTGCATTTTCTGATCTCTAGTCCTATATGAAATA TTTACCTCTAGTGAAACTGATGGAGAATATAAGTAATTAATTCAACTAATTAAATTGCACAAAAATAAGATTA GCCATATCTATTCAGATGCTAAATATACCTACTTCATAGAGGTACAGATTL'TTTTATATACGACTCTAGACCT ACACACTCAAATCAAATTATCGGTGTTTTCTCCTCTACACTCCAATATGAAATGATTATTACTTCTACATGAA ATGCAGGAGTTTEAGAAGGATCAAATTTGACTAAATTTTTTCAATTCTACATTTAAGAAACACTRRTTTT CA GCTAGTTACATTTTTTTATTTCACGAGCTTACATTGACCATGAAAAATACTTGGCACTACTTACTAATTCCCA GGAGG7AGTGAAAATAATATAGATACAAAAACGAAATA7CCTATGTTGTGTGA7ATACTATAATCACAATCAA AAACAGGATTCCTACAAAAGTAATTAGCCATCATAGCAACTCATTCCTTCGGGTAACTCTATAGCACAATCAT AAATTTCTTTAGATATGTATCTGTAAATTAGATTCTTAAAGTTAAATATGAAATTTCATTGGTATTTATGTTT TATATAATAAAAATTAATCCAGCCTTTGCATCTATCATRTGTCCAGACATCCTTGTTATTTGTGATATTTAAC TMULTTTACATAATTATACATC GTTCTTTTTATTTAACACTGTAAATTTCAAATCCTACATGTTATAAAG GTACTATATTTCCTG RC_AAACAGAGTATCGCGTTGGGCTCATTCCATCAACGCATGGAGATATTTACAGCTA AATTC ΓAGTGCTGGAAATAGTAACCCGGAAGCCGCCAACTGACAGTACATTCAGACCCGATTTCGGCCTCCCT TACGTTGAACTGGGCCTACATGGCAGAGTGACGGATGTTGTTGACACGAAGCTCATTTTGGATTCTGAGAACT TCAACAGTAC_AAATAATTCTCCATGTAGAAGAATCACTGAATGCATTGTTTGGCTGCTTAGACTTGGGTTGTC CTCΓCAGGAATTCCCATCGAGTAGAACGCCAACCGGAGATATCATCCACGAACTGAATGCCATCAAACAGAAT TCCGGATTGTTTCCAGTGTCTGAAGGTGGGAGCCTTGAATTCTGA SEQ. ID. No.4 1025 amino acids A MISLPL FV LFSA CPSSS 23 B DDDGDAAGDEI_AI_I.SFKSSI_ YQGGC;SLASWN 55 TSGHGQHCTWVGWCGRRRRRHPHR 80 GAPSRTSMKGHP VSYSQ VKATDG 707 FAPTNLLGSGSFGSVYKGKZ.N1QDHVAVKVLKLENPKAXJSFTA 751 ECEALRNMRHRN VKIVTICSSΣDNRGNDFKAIVYDFMPNGSLE 795 DWΣHPETNDQADQRHLNI_HRRVTII DVACALDYI_HRHGPEPVV 839 KCOZKSSNVLLOSDHVAHVGDFGLARZLVDGTSLZQQSTS 879 SMGFZGTZGYAAP/EYGVG ZASTHGDZYSYGZ V EZ 916 VTGKRPTDSTFRPDLGLRQYVE G HGRVTDWDTK Σ DSENW 960 NSTNNSPCRRITECIV LRLGLSCSQE PSSRTPTGDIIDE 1004 NAΣ QNLSGLFPVCEGGSΣ.EF 1025 SEQ. ID. No. 5 TCAAGCAACAATTTGTCAGGNCA A/G AT A/C/T CC SEQ. ID. No.6 TAACAGCACATTGCTTGATTTNAN G/ATCNCG G/A TG SEQ. ID. No.7 TAA CAG CAC ATT GCTTGA TTTNAN (G/A)TC (G/A)CA (G/A)TG SEQ. ID. No.8 TAACAG CAC ATT GCTTGATTTNAN(G/A)TC (T/C)CT(G/A)TG SEQ. ID. No.9 TAAGCAACAATTTG SEQ. ID. No.10 TAACAGCACATTGCTTGA SEQ. ID. No. 11 TRKl open reading frame (DNA sequence) TCGACGTCGAACAATCGCTTGTCTGGTGCACΓTCCTAGTGCTATTGGAAA CTATTCAGGGCTGAAGAATCTTGTGTTAACTGGAAATGGTTTCTCAGGTG ATATCCCΓTCTGATATTGGCAGACTAAAGAGCATCTTAAAGCTGGACCTG AGTAGAAACAACΓTCTCTGGCACAATCCCTCCTCAGATTGGTAACTGTCT TTCCΓTAACΓTACTTGGATΓTGAGCCAAAATCAACΓΓTCTGGTCCTATCC CAGTTCAAATΓGCΓCAAATTCACATCTTAAATTACATCAATATTTCCTGG AATCACΓΓCAACGAGAGCCTTCCCGCGGAGATTGGCTTGATGAAGAGTTT AACTΓCAGCAGATTTTTCCCACAATAACTTATCTGGATCAATACCTGAAA CAGGCCAATATΓTATATTTCAACTCAACΓΓCCTTCACCGGCAACCCTTAT CTCTCTGGATCCGACTCGACTCCTAGCAACATTACATCCAACTCACCGTC AGAACTTGGAGACGGAAGTGACAGCAGAACTAAGGTTCCTACAATATACA AGTTCATATTTGCATTΓGGGCΓCITATTCTGCΓCCCΓCATTTTCGTTGTC TTAGCAATAATCAAGACAAGAAAGGGGAGTAAGAATTCAAATTTGTGGAA GCTGACAGCATTTCAGAAGCTTGAGTTCGGAAGTGAAGACGTCTTGCAGT GCTTGAAAGACAACAACGTCATAGGGAGAGGTGGAGCAGGGATAGTGTAT AAGGGAACTATGCCAAATGGTGATCATGTCGCGGTGAAGAAATTGGGAAT AAGCAAAGGCΓCACATGATAACGGCCTATCTGCTGAACTTAACACATTAG GGAAGATCAGGCATAGGTACATTGTGAGACTGCTCGCGTTTTGTTCAAAC AAGGAAGTCAACTTGCTAGTTTATGAGTACATGCTAAATGGAAGCΓTAGG TGAAGTGCTTCATGGGAAGAACGGCGGGCAACTCCAATGGGAAACTAGGC TAAAAATAGCCATAGAAGCTGCCAAGGGCCTTTCTTATTTGCACCACGAT TGCTCCCCTATGATAATCCACCGCGATGTCAAGTCCAACAATATATTGTT GAACrCTGAACTTGAAGCTCATGTTGCAGATTTTGGATTAGCCAAGTACT TTCGTAACAATGGTACCTCTGAGTGCATGTCTGCAATTGCAGGATCTTAT GGCTACATTGCTCCAGAATATGCATACACGCTGAAAATTGATGAGAAAAG CGATGTGTATAGCTTTGGAGTGGTGTTGTTGGAGCTTATAACAGGACGAA GGCCAGTAGGAAATTTTGGAGAAGAAGGAATGGACATTGTACAATGGGCG AAAACGGAGACAAAATGGAGCAAAGAAGGGGTGGTGAAAATCTTGGATGA GAGGCTAAAAAATGTTGCAATTGTTGAAGCTATGCAAGTATTTTTTGTAG CAATGCTTTGTGTTGAAGAGTACAGCATTGAGAGGCCTACAATGAGGGAA GTAGTCCAAATGCTTTCTCAAGCTAAACAACCAAATACTTTCCAAATCCA ATAA SEQ. ID. No. 12 STS LNRI^GALPSAIGNYSGLKNLVLTGNGFSGDIPSDIGRIJCSILKLDLSRNNFSGΗ PPQIGNCLSLTYIJDLSQNQLSGPIPVQIAQIHILNYIMSWNHFNESLPAEIGLMKSLT SADFSHNNLSGSIPETGQYLYFNSTSFTGNPYLSGSDSTPSNΓΓSNSPSELGDGSDSRT KΛΦΗYKFFFAFGLLFCSLIFVVLAIIKTRKGSKNSNLWKLTAFQKLEFGSEDVLQCL KDNNVGRGGAGIVYKGTMPNGDHVARSAGFAAASSRGGIVYKGTMPNGDHVAVK _ _,GISKGSHDNGLSAELNTLGKIRHRYIVRLLAFCSNKEVNLLVYEYMLNGSLGEV LHGKNGGQLQWETRLKIAIEAAKGLSYLHHDCSPMΠHRDVTCSNNILLNSELEAHV ADFGLAKYFRNNGTSECMSAIAGSYGYIAPEYAYTLKIDEKSDVYSFGVVLLELΓΓG RRPVGNFGEEGMDΓVQWAKTETKWSKEGVV LDERLKNVAIVEAMQVFFVAML CVEEYSIERPTMREVVQMLSQAKQPNTFQIQ SEQ. ID. No. 13 TRLl DNA sequence TCAAGCAACAATTTRTCAGGACAAATACCTTCAGGCTTGGCCAATGTGAC CACACTGGCAGCATΓTAACGTTTCTTTCAATAATCTGTCTGGGCCACTGC CTCTTAACAAAGATTΓGATGAAGTGTAATAGTGTTCAGGGAAACCCCTTT CTGCAATCGTGCCATGTATTTTCTCTATCAACACCTTCTACAGATCAGCA GGGAAGAATAGGGGACTCACAAGATTCTGCTGCGTCTCCTTCAGGTTCAA CCCAGAAAGGAGGGTGCAGCGGTTTCAACTCCATAGAGATTGCATCCATA ACATCΓGCGGCAGCΓATΓGTGTCAG'I'ΓCΓΓ IUGCTCTGATAGTCCTGTT CΓTTTACACCAGAAAATGGAATCCAAGATCTAGAGTTGCTGGATCTACCA GGAAAGAAGTCACAGTGTTΓACAGAAGTTCCGGTTCCTTTAACATTTGAA AATGTAGTGCGGGCCACAGAGATCTCAAATCAAGCAATGTGCTGTT

Claims: WHAT IS CLAIMED IS: 1. An isolated nucleic acid construct comprising an RRK polynucleotide sequence, which polynucleotide hybridizes to SEQ. ID. No. 1 or to SEQ. ID. No. 3 under stringent conditions. 2. The nucleic acid construct of claim 1, wherein the RRK polynucleotide sequence encodes an RRK polypeptide having an leucine rich repeat motif. 3. The nucleic acid construct of claim 1, wherein the RRK polynucleotide sequence encodes an RRK polypeptide having a cytoplasmic protein kinase domain. 4. The nucleic acid construct of claim 1 , wherein the polynucleotide sequence is a full length gene. 5. The nucleic acid construct of claim 1, wherein the RRK polynucleotide sequence is an Xall gene which encodes an Xall polypeptide as shown in SEQ. ID. No. 2. 6. The nucleic acid construct of claim 5, wherein the Xall polynucleotide sequence encodes an Xall polypeptide as shown in SEQ. ID. No. 4. 7. The nucleic acid construct of claim 5, wherein the Xall polynucleotide is as shown in SEQ. ID. No. 1. 8. The nucleic acid construct of claim 5, wherein the Xall polynucleotide is as shown in SEQ. ID. No. 3. 9. The nucleic acid construct of claim 1, further comprising a promoter operably linked to the RRK polynucleotide sequence. 10. The nucleic acid construct of claim 9, wherein the promoter is a tissue-specific promoter. 11. The nucleic acid construct of claim 9, wherein the promoter is a constitutive promoter. 12. A nucleic acid construct comprising a promoter sequence from an RRK gene linked to a heterologous polynucleotide sequence. 13. The construct of claim 12, wherein the heterologous polynucleotide sequence is a structural gene which confers pathogen resistance on plants. 14. The construct of claim 12, wherein the promoter is from SEQ. ID. No. 1. 15. A transgenic plant comprising a recombinant expression cassette comprising a plant promoter operably linked to a Xall polynucleotide sequence. 16. The transgenic plant of claim 15, wherein the plant promoter is a heterologous promoter. 17. The transgenic plant of claim 15, wherein the plant is rice. 18. The transgenic plant of claim 15, wherein the plant is tomato. 19. The transgenic plant of claim 15, wherein the RRK polynucleotide sequence is an Xall polynucleotide which encodes an Xall polypeptide as shown in SEQ. ID. No. 2 or SEQ. ID. No. 4. 20. The transgenic plant of claim 19, wherein the polynucleotide sequence is as shown in SEQ. ID. No. 1 or in SEQ. ID. No. 3. 21. A method of enhancing resistance to Xanthomonas in a plant, the method comprising introducing into the plant a recombinant expression cassette comprising a plant promoter operably linked to an RRK polynucleotide sequence. 22. The method of claim 21, wherein the plant tissue is from rice. 23. The method of claim 21, wherein the plant tissue is from tomato. 24. The method of claim 21, wherein the polynucleotide encodes an Xall polypeptide as shown in SEQ. ID. No. 2 or SEQ. ID. No. 4. 25. The method of claim 21, wherein the polynucleotide sequence is as shown in SEQ. ID. No. 1 or SEQ. ID. No. 3. 26. The method of claim 21, wherein the promoter is a tissue-specific promoter. 27. The method of claim 21, wherein the promoter is a constitutive promoter. 28. A method of isolating an RRK sequence in a plant, the method comprising: providing DNA prepared from the plant; contacting the DNA with a primer with a sequence from SEQ. ID. No. 1 or SEQ. ID. No. 3; and determining whether amplification has occurred. 29. The method of claim 28, wherein the DNA is cDNA. 30. A sequence from an RRK gene isolated by the method of claim 28. 31. A method of isolating an RRK sequence in a plant, the method comprising providing DNA prepared from the plant; contacting the DNA with a primer with a sequence based on the amino acid sequence of SEQ. ID. No. 2 or SEQ. ID. No. 4; and determining whether amplification has occurred.

Inventors: RONALD PAMELA C, SONG WEN-YUANG, SZABO VERONIQUE, WANG GUO-LIANG, RONALD, PAMELA, C., SONG, WEN-YUANG, Szabo, Veronique, Wang, Guo-Liang
Applicants: RONALD PAMELA C, SONG WEN YUANG, SZABO VERONIQUE, UNIV CALIFORNIA, WANG GUO LIANG, RONALD, PAMELA, C., SONG, WEN-YUANG, Szabo, Veronique, THE REGENTS OF THE UNIVERSITY OF CALIFORNIA, Wang, Guo-Liang
Application year: 1996
Main classification: C12N15
IPC codes: A01H1, A01H5, A01N63, A01N65, A01P3, B65D85, C07K14, C12N5, C12N15, C12Q1