SummaryFlavonoids 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 (eQTL) mapping was performed on the transcript abundance of five downstream PA synthesis genes (dihydroflavonol reductase (VvDFR), leucoanthocyanidin dioxygenase (VvLDOX), leucoanthocyanidin reductase (VvLAR1), VvLAR2 and anthocyanidin reductase (VvANR)) measured by real-time quantitative PCR on a pseudo F1 population in two growing seasons.Twenty-one eQTLs 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 eQTLs for VvDFR, VvLDOX and VvLAR1, gene annotation and a transcriptomic survey suggested that VvMYBC2-L1, a gene coding for an R2R3-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.

Background and Aims:Water deficit is known to influence berry development as well as flavonoid metabolism. The aim of this study was to investigate the influence of pre-and post-veraison water stress on the proanthocyanidin and anthocyanin accumulation on berry samples selected at comparable physiological maturity, especially after veraison while avoiding sugar influence. Methods and Results: Three irrigation treatments were applied by a drip irrigation system on three rows of 30 vines from an experimental Shiraz vineyard. Pre-veraison water stress had no effect on total proanthocyanidin accumulation but increased accumulation of all anthocyanins except malvidin and p-coumaroylated derivatives, whereas post-veraison water stress enhanced the overall anthocyanin biosynthesis, particularly malvidin and p-coumaroylated derivatives. Conclusions: Pre-and post-veraison water stress affected the anthocyanin composition differently, suggesting a differential regulation of the genes involved in the last steps of anthocyanin biosynthesis pathway. Significance of the Study:The study identifies the effect of pre-and post-veraison water stress while avoiding sugar influence on anthocyanin accumulation which could be maximised since both stresses differently impacted hydroxylation and methylation of anthocyanins.

HighlightFunctional analysis of the four grapevine shikimate dehydrogenases (VvSDH1–4) reveals that two of them are involved in gallic acid biosynthesis.

An extraction method on grape berry was optimized for the total flavan-3-ol content measurement with regard to the nature of the sample and the duration of its extraction. This extraction was performed for the first time on the whole pericarp. Flavan-3-ol extractions were achieved on Shiraz ripe samples of pericarp versus skin within different durations: the best results were obtained for the whole pericarp and 1 h duration. Therefore, this more convenient protocol was used to investigate the flavan-3-ol content at different stages through berry development, in parallel with the abundance of transcripts involved in their biosynthesis. Furthermore, flavan-3-ol extractions on pericarp analysis confirmed their presence in both pulp and skin. For the first time, the flavan-3-ol biosynthesis in pulp was demonstrated with both biochemical and transcriptomic analyses since the presence of leucoanthocyanidin reductase (LAR2) and anthocyanin reductase (ANR) transcripts was revealed by real-time PCR. In addition, the percentage of epigallocatechin was different in pulp and skin.