Comparative Transcriptomic and Metabolic Analyses Reveal Temperature Intensity-Dependent Changes in Phenolic Compound Concentrations in Three Wine Grape Cultivars

Global climate change poses a significant threat to viticulture, primarily due to high temperatures. This study examined temperature-induced changes in phenolic profiles in berries of three wine grape cultivars under 25, 35, and 45 °C for 0–48 h using HPLC-ESI-MS/MS. To investigate the molecular response to severe heat stress, transcriptomic analysis was conducted in Cabernet Sauvignon berries subjected to a 45 °C treatment. Results showed that the 45 °C treatment decreased the levels of anthocyanins (particularly delphinidin-3-O-glucoside and cyanidin-3-O-glucoside) in grape berries. Acylated anthocyanins, such as malvidin-3-O-(6-acetyl)-glucoside, exhibited enhanced stability at elevated temperatures. Additionally, high temperatures increased the levels of protocatechuic and gentisic acids and decreased those of rutin, ferulic acid, and p-coumaric acid. Transcriptomic and qRT-PCR analyses revealed that the expression of OMT, LDOX, GST, F3′5′H, and 3AT was positively correlated with changes in anthocyanin levels under high temperatures, suggesting their roles in the observed phenolic alterations. These findings highlight the molecular responses of winegrapes to heat stress, providing a foundation for future viticulture strategies under changing climatic conditions.