Role of chalcone synthase and dihydroflavonol reductase in light dependent accumulation of anthocyanins in 'Toyonoka' strawberry fruits

The effects of light intensity perceived by the fruit surface on anthocyanin biosynthesis were compared between 'Nyoho' and 'Toyonoka' strawberries. Fruit of 'Toyonoka' was collected at green fruit stage (G; 2 weeks after anthesis), white fruit stage (W; about 3 weeks after anthesis), onset of pigmentation (OP; 1-2 days after white fruit stage), pink fruit stage (P; 34 days after white fruit stage), and fun pigmentation stage (FP; 8 days after white fruit stage). The expression of chalcone synthase (CHS) gene was highest at G stage, but remained present during pigmentation. The expression of dihyroflavonol 4-reductase (DFR) gene was low at OP stage and then increased as fruit pigmented. This suggested that DFR but not CHS is involved in developmental regulation of anthocyanin biosynthesis. When fruit of 'Toyonoka' were shaded by wrapping with aluminum foil after W stage, the accumulation of anthocyanin was remarkably reduced. In contrast, shading of 'Nyoho' fruits after W stage did not reduce anthocyanin accumulation. Northern blot analysis showed that the expression of both genes was not affected by fruit shading, suggesting that both CHS and DFR are not involved in light dependent biosynthesis of anthocyanin in 'Toyonoka' strawberry fruits.