Disclosing the Molecular Basis of the Postharvest Life of Berry in Different Grapevine Genotypes

The molecular events that characterize postripening grapevine berries have rarely been investigated and are poorly defined. In particular, a detailed definition of changes occurring during the postharvest dehydration, a process undertaken to make some particularly special wine styles, would be of great interest for both winemakers and plant biologists. We report an exhaustive survey of transcriptomic and metabolomic responses in berries representing six grapevine genotypes subjected to postharvest dehydration under identical controlled conditions. The modulation of phenylpropanoid metabolism clearly distinguished the behavior of genotypes, with stilbene accumulation as the major metabolic event, although the transient accumulation/depletion of anthocyanins and flavonols was the prevalent variation in genotypes that do not accumulate stilbenes. The modulation of genes related to phenylpropanoid/stilbene metabolism highlighted the distinct metabolomic plasticity of genotypes, allowing for the identification of candidate structural and regulatory genes. In addition to genotype-specific responses, a core set of genes was consistently modulated in all genotypes, representing the common features of berries undergoing dehydration and/or commencing senescence. This included genes controlling ethylene and auxin metabolism as well as genes involved in oxidative and osmotic stress, defense responses, anaerobic respiration, and cell wall and carbohydrate metabolism. Several transcription factors were identified that may control these shared processes in the postharvest berry. Changes representing both common and genotype-specific responses to postharvest conditions shed light on the cellular processes taking place in harvested berries stored under dehydrating conditions for several months. Corvina, Sangiovese, Merlot, Oseleta, Syrah and Cabernet Sauvignon berries were collected at full maturity, that was considered the first time point of our experiment (T0, namely time zero of the post-harvest withering process). Syrah and Merlot reached this stage two weeks before the other cultivars. Detached berries were stored under identical controlled environmental conditions until they all reached ~30% weight loss. However, the six cultivars dehydration kinetics greatly differed among each other; the drying process was indeed stopped after ~50 days for Oseleta, Shiraz and Cabernet Sauvignon, after ~70 days for Merlot and after 100 days for Sangiovese and Corvina. In order to monitor the complete dehydration process, berry samples were collected at four time points during the shortest postharvest drying of Oseleta, Shiraz and Cabernet Sauvignon (4 time ponts x 3 biological replicates, namely 12 samples each), at five time points for Merlot (5 time points x 3 biological replicates = 15 samples), and at six time points for the longest drying of Sangiovese and Corvina (6 time points x 3 biological replicates, namely 18 samples each). In total, this work entailed the metabolomic and transcriptomic analysis of 87 samples.