Towards a deep understanding of the function of grape flavonoid regulators VvMYB5a and VvMYB5b

Flavonoids are secondary metabolites that are important for grape and wine quality. The pathway, synthesizing the three major compounds, anthocyanins, tannins and flavonols, is highly regulated in order that different flavonoids are produced in different organs and in various stages of development. Although the branches of flavonoid biosynthetic pathway have been well studied in grapes, little is known about the transcriptional mechanism that regulates the general or shared pathway. Recent studies demonstrate that two MYB transcription factors, VvMYB5a and VvMYB5b, are responsible for the regulation of the early flavonoid structural genes in different stages of berry development (Deluc 2006, 2008). The roles of VvMYB5a and VvMYB5b have been mainly inferred by expression analyses and/or ectopic expression in heterologous systems. To gain information about their functions in the regulatory network operating in Vitis vinifera, two different approaches have been taken.