title: Novel disease resistance specificities result from sequence exchange between tandemly repeated genes at the Cf-4/9 locus of tomato.
abstract: Tomato Cf genes confer resistance to C. fulvum, reside in complex loci carrying multiple genes, and encode predicted membrane-bound proteins with extracytoplasmic leucine-rich repeats. At least two Cf-9 homologs confer novel C. fulvum resistance specificities. Comparison of 11 genes revealed 7 hypervariable amino acid positions in a motif of the leucine-rich repeats predicted to form a beta-strand/beta-turn in which the hypervariable residues are solvent exposed and potentially contribute to recognition specificity. Higher nonsynonymous than synonymous substitution rates in this region imply selection for sequence diversification. We propose that the level of polymorphism between intergenic regions determines the frequency of sequence exchange between the tandemly repeated genes. This permits sufficient exchange to generate sequence diversity but prevents sequence homogenization.
authors.affiliation: The Sainsbury Laboratory, John Innes Centre, Norwich, United Kingdom.
authors.forename: M
authors.initials: M
authors.lastname: Parniske
authors.forename: K E
authors.initials: KE
authors.lastname: Hammond-Kosack
authors.forename: C
authors.initials: C
authors.lastname: Golstein
authors.forename: C M
authors.initials: CM
authors.lastname: Thomas
authors.forename: D A
authors.initials: DA
authors.lastname: Jones
authors.forename: K
authors.initials: K
authors.lastname: Harrison
authors.forename: B B
authors.initials: BB
authors.lastname: Wulff
authors.forename: J D
authors.initials: JD
authors.lastname: Jones
mesh_terms: D000595:Amino Acid Sequence; D001483:Base Sequence; D017124:Conserved Sequence; D017343:Genes, Plant; D014644:Genetic Variation; D007113:Immunity, Innate / Q000235:genetics; D007438:Introns; D007930:Leucine; D008084:Lipoxygenase / Q000737:chemistry; D018551:Solanum lycopersicum / Q000235:genetics*; D008540:Meiosis; D008562:Membrane Glycoproteins / Q000096:biosynthesis / Q000737:chemistry / Q000235:genetics*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D005810:Multigene Family; D010935:Plant Diseases / Q000235:genetics*; D010940:Plant Proteins / Q000096:biosynthesis / Q000737:chemistry / Q000235:genetics*; D011110:Polymorphism, Genetic; D017433:Protein Structure, Secondary; D011995:Recombination, Genetic; D012091:Repetitive Sequences, Nucleic Acid; D016415:Sequence Alignment; D012689:Sequence Homology, Nucleic Acid
chemical_list: C109609:Cf protein, Lycopersicon esculentum; D008562:Membrane Glycoproteins; D010940:Plant Proteins; D008084:Lipoxygenase; D007930:Leucine