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Abstract
Previous results indicated that in grapevine (Vitis vinifera), regulation of the flavonoid
pathway genes by MYB transcription factors depends on their interaction with basic
helix-loop-helix proteins (bHLHs). The present study describes the first functional
characterization of a bHLH factor from grapevine named VvMYC1. This transcription
factor is phylogenetically related to Arabidopsis bHLH proteins, which participate
in the control of flavonoid biosynthesis and epidermal cell fate. Transient promoter
and yeast two-hybrid assays demonstrated that VvMYC1 physically interacts with MYB5a,
MYB5b, MYBA1/A2, and MYBPA1 to induce promoters of flavonoid pathway genes involved
in anthocyanin and/or proanthocyanidin (PA) synthesis. Additionally, transient promoter
assays revealed that VvMYC1 is involved in feedback regulation of its own expression.
Transcript levels of VvMYC1 during berry development correlate with the synthesis
of anthocyanins and PAs in skins and seeds of berries, suggesting that VvMYC1 is involved
in the regulation of anthocyanins and PA synthesis in these organs. Likewise, transient
expression of VvMYC1 and VvMYBA1 induces anthocyanin synthesis in grapevine suspension
cells. These results suggest that VvMYC1 is part of the transcriptional cascade controlling
anthocyanin and PA biosynthesis in grapevine.