Characterization of a Grapevine R2R3-MYB Transcription Factor That Regulates the Phenylpropanoid Pathway

Abstract

The ripening of grape (Vitis vinifera) berry is characterized by dramatic changes in gene expression, enzymatic activities, and metabolism that lead to the production of compounds essential for berry quality. The phenylpropanoid metabolic pathway is one of the components involved in these changes. In this study, we describe the cloning and functional characterization of VvMYB5a, a cDNA isolated from a grape L. cv Cabernet Sauvignon berry library. VvMYB5a encodes a protein belonging to a small subfamily of R2R3-MYB transcription factors. Expression studies in grapevine indicate that the VvMYB5a gene is mainly expressed during the early steps of berry development in skin, flesh, and seeds. Overexpression of VvMYB5a in tobacco (Nicotiana tabacum) affects the expression of structural genes controlling the synthesis of phenylpropanoid and impacts on the metabolism of anthocyanins, flavonols, tannins, and lignins. Overexpressing VvMYB5a induces a strong accumulation of several phenolic compounds, including keracyanin (cyanidin-3-rhamnoglucoside) and quercetin-3-rhamnoglucoside, which are the main anthocyanin and flavonol compounds in tobacco. In addition, VvMYB5a overexpression increases the biosynthesis of condensed tannins and alters lignin metabolism. These findings suggest that VvMYB5a may be involved in the control of different branches of the phenylpropanoid pathway in grapevine.

Ecophysiological, Genetic, and Molecular Causes of Variation in Grape Berry Weight and Composition: A Review

“…The expression profiles of VvMYBA1 in various berry tissues match the changes in expression levels seen for several structural genes of the anthocyanin pathway (Ageorges et al 2006). Apart from VvMBYA1, two other MYB genes, VvMYB5a and VvMYB5b, have been cloned and functionally characterized (Deluc et al 2006(Deluc et al , 2008. Both genes are able to transactivate promoters of several structural genes of the flavonoid pathway, but their expression is different: VvMYB5a is highly expressed before veraison and its transcript level declines after veraison, whereas VvMYB5b transcripts strongly accumulate after veraison, during the ripening stages, supporting the idea of complementary roles for these two genes in anthocyanin accumulation.…”

Light-Induced Expression of a MYB Gene Regulates Anthocyanin Biosynthesis in Red Apples

“…In grapevine, two MYB genes, VvMYBA1 and VvMYBA2, which appear to regulate VvUFGT, contain mutations that segregate with white berries Walker et al, 2006). Other MYBs may activate a broader range of pathways; for example, when the grape gene VvMYB5a was expressed in tobacco (Nicotiana tabacum) it induced biosynthesis of anthocyanins, CTs, flavonols, and lignin (Deluc et al, 2006). However, regulation of anthocyanin synthesis in grapevine may be atypical in several respects compared to other crops.…”

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

“…The bHLH proteins may have overlapping regulatory targets (Zimmermann et al, 2004), but MYB proteins are believed to be key components by allocation of specific gene expression patterns (Stracke et al, 2001). In grape berries, the MYB proteins MYBA1 and MYBA2 (Kobayashi et al, 2002;Walker et al, 2007), MYB5a (Deluc et al, 2006), MYB5b (Deluc et al, 2008), and MYBPA1 act together with bHLH proteins and probably WDR proteins to control anthocyanin and/or PA synthesis. Most R2R3-MYB factors regulating flavonoid biosynthesis (except flavonol synthesis) depend on cofactors, including WDR proteins but, most importantly, a small subgroup of bHLH proteins that share a common motif in their N termini that interacts with a signature motif in the R3 repeat of the N-terminal R2R3 domain of MYB factors (Grotewold et al, 2000).…”