Anthocyanin biosynthetic genes are coordinately expressed during red coloration in apple skin

Five genes of anthocyanin biosynthetic enzymes, chalcone synthase (CHS; EC 2.3.1.74), flavanone 3-hydroxylase (F3H; EC 1.14.11.9), dihydroflavonol 4-reductase (DFR; EC 1.1.1.219), anthocyanidin synthase (ANS; EC 1.14.11.X), and UDP glucose:flavonoid 3-O-glucosyltransferase (UFGluT; EC 2.4.1.X), were isolated, and their expression was investigated to elucidate the molecular mechanism for red coloration in apple 〚Malus sylvestris (L.) Mill. var. domestica (Borkh.) Mansf.〛 skin. In ‘Orin,’ a yellow apple cultivar, no significant levels of anthocyanin were detectable, whereas in ‘Jonathan’ and ‘Fuji,’ both red apple cultivars, anthocyanin concentrations increased during fruit development. At the ripe stage, the level of anthocyanin concentration was about three times higher in ‘Jonathan’ than in ‘Fuji.’ The accumulation of transcripts for the five genes was induced at the later developmental stages in all three cultivars. The levels for the expression of the five genes basically corresponded to the anthocyanin concentrations; that is, the induction of the genes in ‘Orin’ was less pronounced, and that in ‘Fuji’ and ‘Jonathan’ was notable, with much higher expression levels in ‘Jonathan’ than in ‘Fuji’. These results indicate that the five genes are coordinately expressed during fruit development and that their levels of expression are positively related to the degree of anthocyanin concentration. This is the first report that characterizes the relationship between the expression of anthocyanin biosynthetic genes and apple fruit coloration.