MYB diplotypes at the color locus affect the ratios of tri/di-hydroxylated and methylated/non-methylated anthocyanins in grape berry skin

Color variation in grape skin is mainly determined by the quantity and composition of anthocyanins. Anthocyanin quantities are mainly determined by the myeloblastosis (MYB) diplotypes at the color locus. We investigated whether MYB diplotypes also control the anthocyanin composition. Using a population derived from an interspecific hybrid (Vitis labruscana x Vitis vinifera) cross, we performed quantitative trait locus (QTL) analyses for the ratios of tri/di-hydroxylated and methylated/non-methylated anthocyanins. We detected the color locus on LG2 as a major QTL for the ratio of tri/di-hydroxylated anthocyanins. We also found two major QTLs, the color locus on LG2 and a region close to the anthocyanin O-methyltransferase (AOMT) locus on LG1, for the ratio of methylated/non-methylated anthocyanins. Using the same population and a population from another interspecific hybrid cross, we investigated the relationship between the genotypes of the markers closest to the major QTLs, the ratios of tri/di-hydroxylated and methylated/non-methylated anthocyanins, and the expression levels of the genes for flavonoid 3',5'-hydroxylase (F3'5'H), flavonoid 3'-hydroxylase (F3'H), and AOMT. We suggest that MYB diplotypes at the color locus affect the ratio of tri/di-hydroxylated anthocyanins through trans-regulation of F3'5'H/F3'H expression ratio. We also suggest that MYB diplotypes and the AOMT genotypes affect the ratio of methylated/non-methylated anthocyanins through the regulation of AOMT expression. Our findings provide new knowledge about the genetic control of anthocyanin composition and contribute to a better understanding of the genetic mechanisms that control grape skin color.