ZeMYB9 regulates cyanidin synthesis by activating the expression of flavonoid 3'-hydroxylase gene in .

Petal color in is characterized mainly by anthocyanin accumulation. The difference in the content of anthocyanins, especially cyanidins, affects petal coloration in , but the underlying regulatory mechanism remains elusive. Here, we report one R2R3-MYB transcription factor from subgroup 6, ZeMYB9, acting as a positive regulator of anthocyanin accumulation in . Up-regulated expression of and flavonoid 3'-hydroxylase gene () was detected in the cultivar with higher cyanidin content. ZeMYB9 could specifically activate the promoter of , and over-expression of induces much greater anthocyanin accumulation and higher expression level of anthocyanin biosynthetic genes in both petunia and tobacco. And then, ZeMYB9 was demonstrated to interact with ZeGL3, a bHLH transcription factor belonging to IIIf subgroup. Promoter activity of was significantly promoted by co-expressing and compared with expressing alone. Moreover, transient co-expression of and induced anthocyanin accumulation in tobacco leaves. Our results suggest that ZeMYB9 could enhance cyanidin synthesis and regulate petal color in though activating the expression of , by itself or interacting with ZeGL3.