Abstract
Proanthocyanidins (PAs) and anthocyanins are two vital groups of flavonoid compounds for grape berries and red wines. Several transcription factors (TFs) have been identified to be involved in regulating PA and anthocyanin biosynthesis in grape berries. However, research on TFs with different regulatory mechanisms for these two biosynthesis branches in grapes remains limited. In this study, we identified an R2R3-MYB TF, VviMYB86, whose spatiotemporal gene expression pattern in grape berries coincided well with PA accumulation but contrasted with anthocyanin synthesis. Both in vivo and in vitro experiments verified that VviMYB86 positively regulated PA biosynthesis, primarily by upregulating the expression of the two leucoanthocyanidin reductase (LAR) genes in the Arabidopsis protoplast system, as well as in VviMYB86-overexpressing grape callus cultured under 24 h of darkness. Moreover, VviMYB86 was observed to repress the anthocyanin biosynthesis branch in grapes by downregulating the transcript levels of VviANS and VviUFGT. Overall, VviMYB86 is indicated to have a broad effect on flavonoid synthesis in grape berries. The results of this study will help elucidate the regulatory mechanism governing the expression of the two LAR genes in grape berries and provide new insights into the regulation of PA and anthocyanin biosynthesis in grape berries.
Highlights
Flavonoids are an important group of secondary metabolites in plants; they include proanthocyanidins (PAs, known as condensed tannins), anthocyanins, and flavonols, that largely accumulate in the berries, seeds, leaves, flowers, and bark of many plant species (Dixon et al, 2005)
To explore additional putative transcription factors (TFs) involved in regulating PA biosynthesis, especially the expression of the genes encoding leucoanthocyanidin reductase (LAR) in grape berries, we reanalyzed the RNA sequencing (RNA-seq) database of the whole developmental period of Cabernet Sauvignon (CS) berries deposited by Sun et al
Phylogenetic analysis demonstrated that VviMYB86 was clustered with MdMYB6 and AtMYB60, and these TFs all had a negative effect on anthocyanin biosynthesis in planta (Figure 1B)
Summary
Flavonoids are an important group of secondary metabolites in plants; they include proanthocyanidins (PAs, known as condensed tannins), anthocyanins, and flavonols, that largely accumulate in the berries, seeds, leaves, flowers, and bark of many plant species (Dixon et al, 2005). For grape berries and red wines, PAs and anthocyanins strongly contribute to the astringent taste and red coloration, respectively (Peters and Constabel, 2002; Vidal et al, 2003). Both PAs and anthocyanins confer potential beneficial effects on human health due to their antioxidant capacities and radical scavenging functions (Cos et al, 2004; Butelli et al, 2008). The biosynthesis and regulation of PAs and anthocyanins in grape berries have attracted considerable amounts of attention (Cavallini et al, 2015; Wei et al, 2020)
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