Homologues of the Cf-9 disease resistance gene (Hcr9s) are present at multiple loci on the short arm of tomato chromosome 1

The tomato Cf-4 and Cf-9 genes map at a genetically complex locus on the sh ort arm of chromosome 1 and confer resistance against Cladosporium fulvum t hrough recognition of different pathogen-encoded avirulence determinants. C f-4 and Cf-9 are members of a large gene family (Hcr9s, Homologues of Clado sporium fulvum resistance gene Cf-e), some of which encode additional disti nct recognition specificities. A genetic analysis of the majority of Hcr9s suggests that their distribution is spatially restricted to the short arm o f chromosome 1. Two loci of clustered Hcr9 genes have been analyzed physica lly that mapped distal (Northern Lights) and proximal (Southern Cross) to t he Cf-4/9 locus (Milky Way). Sequence homologies between intergenic regions at Southern Cross and Milky Way indicate local Hcr9 duplication preceded c luster multiplication. The multiplication of clusters involved DNA flanking Hcr9 sequences as indicated by conserved lipoxygenase sequences at Souther n Cross and Milky Way. The similar spatial distribution of Hcr9 clusters in different Lycopersicon spp. suggests Hcr9 cluster multiplication preceded speciation.