Altitudinal regulation of flavonoid biosynthesis in <i>Vitis vinifera</i> : unraveling the <scp>VvbHLH88</scp> ‐ <scp>VvUFGT</scp> module driving anthocyanin accumulation

Flavonoids, as vital secondary metabolites, improve grape (Vitis vinifera L.) berry quality and shape wine flavor. Characterized by intense ultraviolet radiation and large diurnal temperature shifts, the high-altitude regions of Southwest China are well-suited for growing late-ripening grapes like Cabernet Sauvignon. However, how altitude influences flavonoid composition and the molecular mechanisms governing these changes remains poorly understood. In this study, we combined transcriptomic analysis with flavonoid profiling to monitor grape berry skins at four key developmental stages (from green berry to harvest) under two typical altitude gradients. Of the genes related to flavonoids, VvbHLH88 was identified as a candidate transcription factor related to the biosynthesis of anthocyanins (a class of flavonoids) by comparing skins from grapes grown at high and low altitudes. Determination of the anthocyanin content in wounded tissues of VvbHLH88-overexpressing and -silenced grape revealed that VvbHLH88 was a positive regulator of anthocyanin biosynthesis. Transcriptome analysis of VvbHLH88-overexpressing healing tissues showed that the expression of anthocyanin synthesis branching enzyme genes was upregulated. In addition, VvbHLH88 directly bound to the promoter of the UDP-glucoflavone-3-O-glucosyltransferase (VvUFGT) gene and activated its transcriptional regulation of anthocyanin synthesis. Consequently, these results uncover specific molecular pathways and transcriptional networks through which high-altitude ecological factors modulate flavonoid metabolism in grape berries, advancing our theoretical understanding of how environmental cues influence metabolic regulation and fruit quality.