Abstract
BackgroundLight conditions significantly influence grape berry ripening and the accumulation of phenolic compounds, but the underlying molecular basis remains partially understood. Here, we applied integrated transcriptomics and pathway-level metabolomics analyses to investigate the effect of cluster bagging during various developmental stages on phenolic metabolism in Cabernet Sauvignon grapes.ResultsBagging treatments had limited effects on berry quality attributes at harvest and did not consistently affect phenolic acid biosynthesis between seasons. Significantly elevated flavan-3-ol and flavonol contents were detected in re-exposed berries after bagging during early-developmental stages, while bagging after véraison markedly inhibited skin anthocyanin accumulation. Several anthocyanin derivatives and flavonol glycosides were identified as marker phenolic metabolites for distinguishing bagged and non-bagged grapes. Coordinated transcriptional changes in the light signaling components CRY2 and HY5/HYHs, transcription regulator MYBA1, and enzymes LAR, ANR, UFGT and FLS4, coincided well with light-responsive biosynthesis of the corresponding flavonoids. The activation of multiple hormone signaling pathways after both light exclusion and re-exposure treatments was inconsistent with the changes in phenolic accumulation, indicating a limited role of plant hormones in mediating light/darkness-regulated phenolic biosynthesis processes. Furthermore, gene-gene and gene-metabolite network analyses discovered that the light-responsive expression of genes encoding bHLH, MYB, WRKY, NAC, and MADS-box transcription factors, and proteins involved in genetic information processing and epigenetic regulation such as nucleosome assembly and histone acetylation, showed a high positive correlation with grape berry phenolic accumulation in response to different light regimes.ConclusionsAltogether, our findings provide novel insights into the understanding of berry phenolic biosynthesis under light/darkness and practical guidance for improving grape features.
Highlights
Light conditions significantly influence grape berry ripening and the accumulation of phenolic compounds, but the underlying molecular basis remains partially understood
There was no significant difference in the content of total soluble solids (TSS) in berries from each developmental stage among treatments during the two years (Fig. 2b)
We performed an integrated transcriptomics and pathway-level metabolomics analysis to investigate the effect of cluster bagging during various developmental stages on grape phenolic metabolism
Summary
Light conditions significantly influence grape berry ripening and the accumulation of phenolic compounds, but the underlying molecular basis remains partially understood. Phenolic acids [mainly hydroxybenzoic acids (HBAs) and hydroxycinnamic acids (HCAs)], flavonoids (mainly flavan-3-ols, anthocyanins, and flavonols), and nonflavonoid polyphenols (mainly resveratrols) are three major classes of phenolic compounds detected in grapes and wine [16, 17]. The response of skin anthocyanins to sunlight exposure treatments is variable and heavily dependent on the timing and degree of severity [14, 35] It appears that early leaf removal or cluster thinning induces a substantial acceleration of anthocyanin biosynthesis and a higher anthocyanin concentration [10, 36,37,38,39], whereas excessive solar radiation/irradiance causes sunburn damage and is not conducive to optimal anthocyanin accumulation in berries [12, 15, 21, 33, 40, 41]
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