An R2R3-MYB Transcription Factor FtMYB15 Involved in the Synthesis of Anthocyanin and Proanthocyanidins from Tartary Buckwheat

Tartary buckwheat is an excellent medicinal and nutrient-rich crop that contains abundant flavonoids. Flavonoids, such as anthocyanin and proanthocyanidin, can be accumulated in plants for resistance to abiotic stresses, for instance, UV-B and cold. In this study, an R2R3-MYB transcription factor gene named FtMYB15 was isolated from tartary buckwheat. A phylogenetic tree suggested that FtMYB15 potentially plays a role in flavonoid biosynthesis. Consequently, the ectopic overexpression of FtMYB15 was conducted in Arabidopsis. Transgenic lines exerted increased pigmentation in leaves and seed coats, as well as higher accumulation levels of anthocyanin and proanthocyanidin in Arabidopsis. Specifically, anthocyanin and proanthocyanidin in transgenic lines were 8.62- and 4.93 (P < 0.01)-fold higher than wild-type Arabidopsis, respectively. Meanwhile, the expressions of both early and late biosynthesis genes, including AtCHS, AtCHI, AtF3H, AtF3'H, AtDFR, AtANS, AtBAN, and AtTT12, in the anthocyanin and proanthocyanidin pathway were enhanced (P < 0.01). Particularly, AtDFR and AtANS were upregulated 4.13 and 5.11 (P < 0.01) times higher than the control, respectively, whereas AtBAN and AtTT12 were upregulated a 100-fold (P < 0.01) compared to wild-type Arabidopsis. Only AtFLS expression decreased in transgenic Arabidopsis (P < 0.01). These results laid a foundation for better understanding of flavonoid biosynthesis and its molecular regulation mechanism in tartary buckwheat.