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

The Cf genes in tomatoes are responsible for resistance against Cladosporidium fulvum. There are several copies of this gene and 11 of these copies were analyzed for amino acid composition. Results revealed seven hypervariable amino acid residues in the leucine-rich domain. The predicted structure of the protein exposes these residues to the solvent. Further analysis of this domain reveals selection for sequence diversification.