Metabolomics of Grape Berry Postharvest Withering

Grape postharvest dehydration is a technique used to enhance specific berry quality traits for the production of special wines. In Verona (Italy) province this technique is traditionally employed for producing premium wines like Amarone, obtained mainly from Corvina grape characterized by the capability to withstand a long period of postharvest dehydration.Many of the modification affecting berries during postharvest withering are obviously related to water loss and consequent berry juice concentration. However, since the cells of the berries keep the ability to modulate their gene expression for a long time during the dehydration process, many other peculiar traits of dehydrated grapes are achieved in berries which are, at least in part, under strict genetic control. From the point of view of grape berry cells, the dehydration process is characterized by severe stresses probably partially overlapped, at least at the beginning of the process, with an extended ripening program.In order to understand what happens during the postharvest withering process in different grape varieties that differ for the withering performances we analyzed and compared transcriptomics and metabolomics changes during the process in Corvina, Sangiovese, Oseleta, Merlot, Cabernet Sauvignon and Shiraz, placed in the same environmental conditions. The untargeted metabolomics analyses reveal that, besides the obvious metabolite concentration due to the water loss, only in some varieties the “constructive” processes (de novo accumulation of certain metabolites) prevail on the metabolite degradation. Furthermore, a general dramatic rearrangement of the berry transcriptome was observed during the postharvest period in all grapes. Corvina was characterized by a much higher induction of gene expression compared to the other cultivars. Moreover, in this cultivar the highest metabolite and gene expression modulation require a long lasting process, being abolished by artificially induced short withering.