Poplar MYB117 promotes anthocyanin synthesis and enhances flavonoid B-ring hydroxylation by up-regulating the flavonoid 3 ',5 '-hydroxylase gene

: Ma Dawei, Tang Hao, Reichelt Michael, Piirtola Eerik-Mikael, Salminen Juha-Pekka, Gershenzon Jonathan, Constabel C Peter

Publisher: OXFORD UNIV PRESS

: 2021

: Journal of Experimental Botany

: JOURNAL OF EXPERIMENTAL BOTANY

: J EXP BOT

: 72

: 10

: 3864

: 3880

: 17

: 0022-0957

DOI: https://doi.org/10.1093/jxb/erab116

Flavonoids, such as anthocyanins, proanthocyanidins, and flavonols, are widespread plant secondary metabolites and important for plant adaptation to diverse abiotic and biotic stresses. Flavonoids can be variously hydroxylated and decorated; their biological activity is partly dependent on the degree of hydroxylation of the B-ring. Flavonoid biosynthesis is regulated by MYB transcription factors, which have been identified and characterized in a diversity of plants. Here we characterize a new MYB activator, MYB117, in hybrid poplar (Populus tremulaxtremuloides). When overexpressed in transgenic poplar plants, MYB117 enhanced anthocyanin accumulation in all tissues. Transcriptome analysis of MYB117-overexpressing poplars confirmed the up-regulation of flavonoid and anthocyanin biosynthesis genes, as well as two flavonoid 3',5'-hydroxylase (F3'5'H) genes. We also identified up-regulated cytochrome b(5) genes, required for full activity of F3'5'H . Phytochemical analysis demonstrated a corresponding increase in B-ring hydroxylation of anthocyanins, proanthocyanidins, and flavonols in these transgenics. Similarly, overexpression of F3'5'H1 directly in hybrid poplar also resulted in increased B-ring hydroxylation, but without affecting overall flavonoid content. However, the overexpression of the cytochrome b(5) gene in F3'5'H1-overexpressing plants did not further increase B-ring hydroxylation. Our data indicate that MYB117 regulates the biosynthesis of anthocyanins in poplar, but also enhances B-ring hydroxylation by up-regulating F3'5'H1.