The Grapevine R2R3-MYB Transcription Factor VvMYBF1 Regulates Flavonol Synthesis in Developing Grape Berries

Abstract

Flavonols are important ultraviolet light protectants in many plants and contribute substantially to the quality and healthpromoting effects of fruits and derived plant products. To study the regulation of flavonol synthesis in fruit, we isolated and characterized the grapevine (Vitis vinifera 'Shiraz') R2R3-MYB transcription factor VvMYBF1. Transient reporter assays established VvMYBF1 to be a specific activator of flavonol synthase1 (VvFLS1) and several other promoters of grapevine and Arabidopsis (Arabidopsis thaliana) genes involved in flavonol synthesis. Expression of VvMYBF1 in the Arabidopsis mutant myb12 resulted in complementation of its flavonol-deficient phenotype and confirmed the function of VvMYBF1 as a transcriptional regulator of flavonol synthesis. Transcript analysis of VvMYBF1 throughout grape berry development revealed its expression during flowering and in skins of ripening berries, which correlates with the accumulation of flavonols and expression of VvFLS1. In addition to its developmental regulation, VvMYBF1 expression was light inducible, implicating VvMYBF1 in the control of VvFLS1 transcription. Sequence analysis of VvMYBF1 and VvFLS1 indicated conserved putative light regulatory units in promoters of both genes from different cultivars. By analysis of the VvMYBF1 amino acid sequence, we identified the previously described SG7 domain and an additional sequence motif conserved in several plant MYB factors. The described motifs have been used to identify MYB transcription factors from other plant species putatively involved in the regulation of flavonol biosynthesis. To our knowledge, this is the first functional characterization of a light-inducible MYB transcription factor controlling flavonol synthesis in fruit.

Functional Differentiation of the Glycosyltransferases That Contribute to the Chemical Diversity of Bioactive Flavonol Glycosides in Grapevines (Vitis vinifera)

“…The spatial and temporal patterns of Vv GT5 and Vv GT6 cDNA expression were very similar and resembled those of Vv FLS1. These results, along with the fact that Vv GT5 and Vv GT6 genes are located in proximity to one another on the same chromosome, strongly suggest that expression of these two UGT genes is coordinately controlled by common transcription factors in grapevines, which probably include the flavonol-specific MYB transcription factor Vv MYBF1 (Czemmel et al, 2009). …”

“…The results were compared with those of Vv GT1 (Ford et al, 1998), which is responsible for anthocyanin biosynthesis in grapevine berry skin and Vv FLS1 (also termed Vv FLS4), which is responsible for flavonol biosynthesis (Fujita et al, 2006;Czemmel et al, 2009) (Figure 3, left panels). The Vv GT5 transcript was abundant in berry skin and increased at the onset of pigmentation (veraison), with the highest level of transcription detected in the fully pigmented skin (exocarp) of mature berries ( Figure 3, second panel).…”

“…Flavonol aglycons are biosynthesized from dihydroflavonols by the action of flavonol synthase (Vv FLS), a 2-oxoglutarate-dependent dioxygenase, which is temporally regulated by an R2R3-Myb transcription factor, Vv MYBF1 (Fujita et al, 2006;Czemmel et al, 2009). Subsequently, glycosylation of flavonols enhances their water solubility, such that high concentrations of flavonols can accumulate in plant cells.…”

Competition between anthocyanin and flavonol biosynthesis produces spatial pattern variation of floral pigments between Mimulus species

“…2B), was selected to generate a lar1/lar1 homozygous NIL for subsequent transgenic experiments and gene expression analysis. This subgroup of MYB transcription factors is known to regulate flavonol biosynthesis in Arabidopsis, grapevine, and tomato (19)(20)(21)(22), and regulate the biosynthesis of 3-deoxyflavonoids and phlobaphenes in maize (23). Both flavonol and anthocyanin biosynthesis require the same intermediate substrate, dihydroflavonol.…”

Seasonal Abscisic Acid Signal and a Basic Leucine Zipper Transcription Factor, DkbZIP5, Regulate Proanthocyanidin Biosynthesis in Persimmon Fruit

“…These factors can activate an ABREcontaining promoter in an ABA-dependent manner (Uno et al, 2000). However, the involvement of the ABREbinding bZIP TFs in Myb TF expression regulating flavonoid biosynthesis has not yet been demonstrated, although bZIP TFs have been suggested to directly affect the expression of some flavonoid pathway genes such as FLS in Arabidopsis and grapevine (Hartmann et al, 2005;Czemmel et al, 2009;Hichri et al, 2011). Our study showed that ABA signals can act as a regulator of DkMyb4 and the resultant PA biosynthesis via the activity of ABF/AREB/ABI5-like bZIP TFs in specific developmental stages of persimmon fruit.…”