New insight into the genetics of color in grape
Résumé
Grapes may either be white or colored, ranging from the lightest pink to the darkest purple tone depending on the quantity and composition of anthocyanins accumulated in the berry skin. QTL mapping on cross-derived progeny and association mapping on natural diversity were combined to decipher the genetic architecture of anthocyanin content and composition in berry skin, a crucial trait for both wine quality and human nutrition. For the total anthocyanin content in the skin of mature berries on a segregating population of 191 progenies, we identified 2 QTLs accounting for 62% and 7.1% of the total variation. Further studying candidate genes from these QTL intervals on a core collection of natural resources (141 individuals), we identified Myb genes highly associated with total content of anthocyanins. Using a multivariate regression method, we demonstrated that four polymorphisms accounted for 86% of the observed variation, with all these polymorphisms leading to structural changes in the MYB proteins. Skin color tones are not only due to the overall pigment concentration but also to variation in pigment composition, mostly due to hydroxylation, methylation and acylation differences. For all these variations, the major QTL on LG2 played a key role. In addition, specific QTLs were found for each of the composition variable: on LG6, explaining 13% of the hydroxylation variation, on LG1, explaining up to 17% of the methylation variation and on LG7 and LG13, explaining 11 and 7% of the variation in p-coumaric acylation. For the hydroxylation level, the specific QTL on LG6 co-localized with candidate VvF3' 5' H genes and two genic SNPs within two of those genes were identified as associated to the variation. For the methylation variation, the specific QTL on LG1 co-localized with a cluster of O-methyltransferase genes among which VvAOMT3.2 showed a strong association.