Expression analysis of anthocyanin biosynthetic genes in apple skin: Effect of UV-B and temperature

We investigated the expression of the five anthocyanin biosynthetic genes, chalcone synthase (CHS), flavanone 3-hydroxylase (F3H), dihydroflavonol 4-reductase (DFR), anthocyanidin synthase (ANS), and UDP-glucose:flavonoid 3-O-glucosyltransferase (UFGluT) during ripening in five early ripening apple cultivars (‘Iwai’, ‘Sansa’, ‘Tsugaru’, ‘Homei-Tsugaru’, and ‘Akane’), as well as under UV-B and temperature treatments. Anthocyanin biosynthesis increased progressively during ripening, with the onset of rapid accumulation occurring at 107 days after full bloom (DAFB) in the four apple cultivars except ‘Iwai’. Generally, increase in the expression levels of all five biosynthetic genes in fruit skin coincided with increase of anthocyanin concentration. When the fruit was bagged about 1 month prior to commercial harvest to prevent anthocyanin biosynthesis, the expression of CHS, ANS and UFGluT was substantially depressed in fruit skin, whereas that of all five genes including CHS, ANS and UFGluT was enhanced by UV-B and low temperature treatments with the accumulation of anthocyanins. The accumulation level of the main anthocyanin pigment, cyanidin 3-galactoside, in the fruits under UV-B and low temperature treatment, was less than that in the field-ripened fruits, while cyanidin 3-arabinoside was relatively the same level. Our results showed that UV-B and low temperature were important factors for anthocyanin accumulation in apple fruit skin by inducing the expression of the anthocyanin biosynthetic genes, especially CHS, ANS and UFGluT genes.