Expression of anthocyanin biosynthetic genes in Malus sylvestris L. 'Mutsu' non-red apples

The expression of five anthocyanin biosynthetic genes of chalcone synthase (MdCHS), flavanone 3-hydroxylase (MdF3H), dihydroflavonol 4-reductase (pDFR), anthocyanidin synthase (MdANS) and UDP glucose-flavonoid 3-O-glucosyltransferase (pUFGluT) was investigated during fruit development in the skin of non-red 'Mutsu' apples (Malus sylvestris (L.) Mill. var. domestica (Borkh) Mansf.). MdCHS, MdF3H and pDFR appeared in the skin of non-bagged fruit from 81 d after full bloom (DAFB) to 167 DAFB, but MdANS and pUFGluT did not appear. When the fruit was bagged during fruit development and unbagged before the maturation, anthocyanin was produced in the exposed portion but not in the shaded portion. All five genes including MdANS and pUFGluT were detected in the exposed portion at 165 DAFB. In the shaded portion, MdANS was detected, but pUFGluT was not. The skin colour of the shaded portion after unbagging in the bagged fruit was more yellow than that in non-bagged fruit. This result suggests that the yellowing of the skin may relate to the expression of MdANS. All five anthocyanin biosynthetic genes were detected at 20 DAFB despite the absence of anthocyanin. The roles of genes in the anthocyanin biosynthetic pathway may differ from one development stage to the next.