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Grapevine organs accumulate anthocyanins in a cultivar-specific and environmentally induced manner. The MYBA1- A2 genes within the berry color locus in chromosome 2 represent the major genetic determinants of fruit color. The simultaneous occurrence of transposon insertions and point mutations in these genes is responsible for most white-skinned phenotypes; however, the red pigmentation found in vegetative organs suggests the presence of additional regulators. This work describes a genomic region of chromosome 14 containing three closely related R2R3- MYB genes, named MYBA5, MYBA6 and MYBA7. Ectopic expression of the latter two genes in grapevine hairy roots promoted anthocyanin accumulation without affecting other phenylpropanoids. Transcriptomic profiling of hairy roots expressing MYBA1, MYBA6 and MYBA7 showed that these regulators share the activation of late biosynthetic and modification/transport-related genes, but differ in the activation of the FLAVONOID-3′5′- HYDROXYLASE ( F3′5′H) family. An alternatively spliced MYBA6 variant was incapable of activating anthocyanin synthesis, however, because of the lack of an MYC1 interaction domain. MYBA1, MYBA6.1 and MYBA7 activated the promoters of UDP- GLUCOSE: FLAVONOID 3-O- GLUCOSYLTRANSFERASE ( UFGT) and ANTHOCYANIN 3-O- GLUCOSIDE-6″-O- ACYLTRANSFERASE ( 3 AT), but only MYBA1 induced F3′5′H in concordance with the low proportion of tri-hydroxylated anthocyanins found in MYBA6-A7 hairy roots. This putative new color locus is related to the red/cyanidic pigmentation of vegetative organs in black- and white-skinned cultivars, and forms part of the UV-B radiation response pathway orchestrated by ELONGATED HYPOCOTYL 5 ( HY5). These results demonstrate the involvement of additional anthocyanin regulators in grapevine and suggest an evolutionary divergence between the two grape color loci for controlling additional targets of the flavonoid pathway. [ABSTRACT FROM AUTHOR]

Flavonoids are secondary metabolites with multiple functions. In grape ( Vitis vinifera), the most abundant flavonoids are proanthocyanidins ( PAs), major quality determinants for fruit and wine. However, knowledge about the regulation of PA composition is sparse. Thus, we aimed to identify novel genomic regions involved in this mechanism., Expression quantitative trait locus (e QTL) mapping was performed on the transcript abundance of five downstream PA synthesis genes (dihydroflavonol reductase ( Vv DFR), leucoanthocyanidin dioxygenase ( Vv LDOX), leucoanthocyanidin reductase ( Vv LAR1), Vv LAR2 and anthocyanidin reductase ( Vv ANR)) measured by real-time quantitative PCR on a pseudo F1 population in two growing seasons., Twenty-one e QTLs were identified; 17 of them did not overlap with known candidate transcription factors or cis-regulatory sequences. These novel loci and the presence of digenic epistasis support the previous hypothesis of a polygenic regulatory mechanism for PA biosynthesis., In a genomic region co-locating e QTLs for Vv DFR, Vv LDOX and Vv LAR1, gene annotation and a transcriptomic survey suggested that Vv MYBC2- L1, a gene coding for an R2 R3- MYB protein, is involved in regulating PA synthesis. Phylogenetic analysis showed its high similarity to characterized negative MYB factors. Its spatiotemporal expression profile in grape coincided with PA synthesis. Its functional characterization via overexpression in grapevine hairy roots demonstrated its ability to reduce the amount of PA and to down-regulate expression of PA genes. [ABSTRACT FROM AUTHOR]