THE TOMATO CF-5 DISEASE RESISTANCE GENE AND 6 HOMOLOGS SHOW PRONOUNCED ALLELIC VARIATION IN LEUCINE-RICH REPEAT COPY NUMBER

The tomato Cf-2 and Cf-5 genes confer resistance to Cladosporium fulvu m and map to a complex locus on chromosome 6. The Cf-5 gene has been i solated and is predicted to encode a largely extracytoplasmic protein containing 32 leucine-rich repeats (LRRs), resembling the previously i solated Cf-2 gene, which has 38 LRRs. Three haplotypes of this locus f rom Lycopersicon esculentum, L. pimpinellifolium, and L. esculentum va r cerasiforme were compared, and five additional homologs of Cf-5 were sequenced. All share extensive sequence identity, particularly within the C-terminal portions of the predicted proteins. In striking contra st to the Cf-9 gene family, six of seven homologs in the Cf-2/Cf-5 gen e family vary in LRR copy number, ranging from 25 to 38 LRRs. Cf-5 and one adjacent homolog differ by only two LRRs. Recombination events th at vary the LRR copy number in this region could provide a mechanism f or the generation of new specificities for recognition of different li gands. A recombination breakpoint between the Cf-2 and Cf-5 loci was f ully characterized and shown to be intragenic.