Identification of transcripts associated with postharvest withering in Vitis vinifera L. ‘Cabernet Franc’ grape berry
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The withering of grape berries following harvest is known in Italian as appassimento, and it used as a tool to alter the composition of the berries prior to winemaking. Specific gene expression patterns were determined by RNA Sequencing in the red-skinned berries of Vitis vinifera L. ‘Cabernet Franc’ for three time points during withering, at both slow and fast rates, up to 40.7 and 31.2 percent cluster weight loss respectively, with a target of 29 + 1 oBrix. Slow withering was associated with a higher number of differentially expressed genes, and those commonly up-regulated across all time points were associated with a higher number of gene ontology categories, including phenylpropanoid and cellular aromatic compound metabolism and biosynthesis. Commonly up-regulated genes across fast drying were only related to response to abiotic and biotic stimuli terms. Both slow and fast withering were associated with an up-regulation of numerous WRKY and MYB transcription factors, as well as stilbene synthase, phenylalanine ammonia lyase and trehalose-phosphate phosphatase. With respect to anthocyanin biosynthesis, there was no change in expression for MYBA genes, and UDP-glucose:flavonoid 3-O-glucosyltransferase was down-regulated transiently in fast withering and showed no change in expression in slow. Slow withering was also associated with an up-regulation of a dehydrin and the CBF3 gene. The results of the present study suggest that fast withering may be associated with primarily an intense stress response, while slow withering may be associated with a senescence or over-ripening, in combination with a gradual adaptation to a less intense dehydration stress. As such, the influence of rate during withering will likely have a strong impact on the final berry composition, and thus will influence the characteristics of the resulting wines.