Novel disease resistance specificities result from sequence exchange between tandemly repeated genes at the Cf-4/9 locus of tomato

• Published in: Cell 1997-12, Vol.91 (6), p.821-832
• Main Authors: Parniske, M, Hammond-Kosack, K E, Golstein, C, Thomas, C M, Jones, D A, Harrison, K, Wulff, B B, Jones, J D
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; Base Sequence; Conserved Sequence; Genes, Plant; Genetic Variation; Immunity, Innate - genetics; Introns; Leucine; Lipoxygenase - chemistry; Lycopersicon esculentum - genetics; Meiosis; Membrane Glycoproteins - biosynthesis; Membrane Glycoproteins - chemistry; Membrane Glycoproteins - genetics; Models, Molecular; Molecular Sequence Data; Multigene Family; Plant Diseases - genetics; Plant Proteins - biosynthesis; Plant Proteins - chemistry; Plant Proteins - genetics; Polymorphism, Genetic; Protein Structure, Secondary; Recombination, Genetic; Repetitive Sequences, Nucleic Acid; Sequence Alignment; Sequence Homology, Nucleic Acid
• ISSN: 0092-8674
• DOI: 10.1016/s0092-8674(00)80470-5

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.