Evolution of the SH3 locus in coffee species. A. Current organization of the SH3 locus in Coffea canephora (Cc) and C. arabica (sub-genome Ea and sub-genome Ca). B - A model of the evolution of locus SH3 in coffee plants involving genome expansion and retraction by gene duplication and deletions. Gray arrows indicate members of the SH3 family. Open arrows indicate other non-R genes flanking R genes in the locus as numbered in . Short arrows indicate truncated versions of corresponding genes.