RNAi-mediated silencing and overexpression of the FaMYB1 gene and its effect on anthocyanin accumulation in strawberry fruit

Strawberry (Fragaria × ananassa) contains anthocyanins which are important secondary metabolites and key contributors to the antioxidant capacity and nutritional value of the fruit. Anthocyanin biosynthetic genes have been identified. However, the detailed mechanism responsible for anthocyanin accumulation and regulation of biosynthetic genes during strawberry fruit ripening remain unclear. In the present study, we examined the effect of a Fragaria × ananassa myeloblastosis 1 homolog, FaMYB1, on anthocyanin accumulation in the strawberry fruit receptacle. Expression analysis shows that FaMYB1 transcripts increased in response to irradiance but not to abscisic acid treatments. Down-regulation of FaMYB1 was achieved in planta using Agrobacterium-mediated RNA interference (RNAi). As a result, FaMYB1-RNAi fruits exhibited a significant increase in anthocyanin content. Conversely, overexpression of FaMYB1 resulted in a decrease in anthocyanin content. Overexpression of FaMYB1 also significantly reduced expression of genes encoding anthocyanidin synthase and flavonoid glycosyltransferase, whereas down-regulation of FaMYB1 resulted in a significant decrease in the amount of transcripts of leucoanthocyanidin reductase. These data suggest that FaMYB1 might negatively control anthocyanin biosynthesis in the strawberry fruit at the branching-point of anthocyanin/proanthocyanidin biosynthesis.