Changes in flavonoid biosynthesis and in the berry whole transcriptome of 'Sangiovese' under moderate air temperature increase

Among the environmental factors, temperature is the one that poses serious threats to viticulture in the present and future scenarios of global climate change. In this work, we evaluated the effects on berry ripening of two thermal regimes, imposed from veraison to harvest. Potted vines were grown in two air-conditioned greenhouses with high temperature (HT) and low temperature (LT) regimes characterized respectively by 26 and 21°C as average and 41.7 and 35°C as maximum air daily temperature. We carried out analyses of the main berry compositional parameters and of berry skin phenolics on HT and LT berries sampled at six phases during ripening. In the same sampling dates, the berry skin transcriptome under the two temperature regimes was analyzed. The two thermal conditions strongly differentiated HT and LT berries. The HT regime did not increase sugar accumulation at harvest but contributed to a total acidity reduction and to a pH increase. Conversely, changes in growing temperatures greatly impacted on grape phenolic composition as the anthocyanin and flavonol concentrations resulted strongly reduced. Whole transcriptome analysis identified genes with a different expression profile when berries were ripened under HT or LT. Focusing on phenylpropanoid-related genes, we found many differential transcripts involved in stilbene biosynthesis. Nevertheless, the effect observed on genes involved in flavonoid biosynthesis was only marginally in line with the berry biochemical parameters, suggesting a possible post-transcriptional response of this pathway to moderate increments of temperature in 'Sangiovese'.