Candidate gene analysis of anthocyanin pigmentation loci in the Solanaceae

Crop species in the Solanaceae, which includes tomato (Lycopersicon esculentum), potato (Solanum tuberosum), pepper (Capsicum spp.), and eggplant (S. melongena), exhibit natural variation in the types, levels, and tissue-specific expression patterns of anthocyanin pigments. While the identities of the genes underpinning natural variation in anthocyanin traits in these crops are largely unknown, many structural genes and regulators of anthocyanin biosynthesis have been isolated from the solanaceous ornamental species Petunia. To identify candidate genes that may correspond to loci controlling natural variation in the four crops, 13 anthocyanin-related genes were localized on a tomato F-2 genetic map. Gene map positions were then compared to mapped mutants in tomato and through comparative genetic maps to natural variants in potato, eggplant, and pepper. Similar map positions suggest that the tomato mutants anthocyaninless, entirely anthocyaninless, and anthocyanin gainer correspond to flavonoid 3'5'-hydroxylase (f3'5'h), anthocyanidin synthase, and the Petunia Myb domain trancriptional regulatory gene an2, respectively. Similarly potato R, required for the production of red pelargonidin-based pigments, P, required for production of purple delphinidin-based pigments, and I, required for tissue-specific expression in tuber skin, appear to correspond to dihydroflavonol 4-reductase, f3'5'h and an2, respectively. The map location of an2 also overlaps pepper A and eggplant fap10.1, lla10.1, lra10.1, sa10.1, pa10.1 and ca10.1, suggesting that a homologous regulatory locus has been subjected to parallel selection in the domestication of many solanaceous crops. To test the hypothesis that tomato anthocyaninless corresponds to f3'5'h, a portion of the gene was sequenced. A premature stop codon was observed in an anthocyaninless mutant, but not in wild-type.