Gretchen Hagen 3.6-like promotes anthocyanin accumulation by negatively regulating the expression of basic...

Anthocyanins are mainly synthesized from flavonoid precursors in plants. Although there have been numerous studies on the biosynthesis of anthocyanins, few have sought to explore how Gretchen Hagen 3 (GH3) genes regulate the production of anthocyanins. In this study, a VaGH3.6-like gene was identified, and its overexpression in grapevine callus tissues and berry skins promoted significant accumulation of anthocyanins and reduced endogenous IAA content under light conditions, whereas callus tissues transformed with a mutant VaGH3.6-like showed the opposite results. The overexpression of VaGH3.6-like was observed to directly promote the accumulation of flavonoids under dark conditions, whereas the accumulation was significantly reduced in mutants. In addition, the VabHLH106 transcription factor, a negative regulator of VaGH3.6-like, was screened via RNA-seq. Subsequent analyses using Y2H, Y1H, DLR™, and EMSA analyses revealed that VabHLH106 represses VaGH3.6-like expression by directly binding to two E-box elements in its promoter region. Interestingly, VaGH3.6-like overexpression regulates VabHLH106 expression via a negative feedback mechanism, attenuating the repressive effect of VabHLH106 on the downstream genes VvLDOX, VvCYP75B2, and VvCYP73A3, thus leading to an increasing in the synthesis of anthocyanins in grapes. These findings provide a new theoretical basis for further understanding the molecular mechanisms underlying accumulation of anthocyanins in grapes.