WHAT MAKES A RED POTATO RED: IDENTIFYING AMINO ACIDS THAT INFLUENCE SUBSTRATE SPECIFICITY OF POTATO DFR

Pigmented potatoes (Solanum tuberosum L.) are a rich source of anthocyanin pigments. Dihydroflavonol 4-reductase (DFR) is a rate limiting enzyme in the flavonoid pathway that gives rise to the anthocyanin pigments pelargonidin (red), cyanidin (pink) and delphinidin (purple) by reducing dihydrokaempferol (DHK), dihydroquercetin (DHQ) and dihydromyricetin (DHM), respectively. It has previously been shown that dfr corresponds to the R locus in potato, where one specific allele is able to direct synthesis of red pigments and other alleles are unable to do so. To test whether either of two amino acids (alanine at position 143, cysteine at position 154) in a putative substrate binding region determines ability to produce red anthocyanins, six chimeric constructs of dfr were made by reciprocal exchanges between red and non-red alleles. These constructs, as well as wild type red and non-red alleles, were introduced into the potato cultivar Prince Hairy (genotype dddd rrrr P-), which has pale blue flowers. The flowers of engineered lines were monitored for shifts to purple coloration and anthocyanins were analyzed using UHPLC/MS. Although individual amino acid changes altered both flower color and anthocyanin profiles, possessing alanine at position 143 and cysteine at 154 gave the largest effect. Editing both of these positions may be sufficient to convert white potatoes to red potatoes, and vice-versa