VvSnRK1-Mediated VvMYBC2-L1 Phosphorylation in Repressing Anthocyanin Accumulation Under High Temperature in Grapevine

Global climate change has aggravated heat stress throughout the grape growing season, which reduces anthocyanin accumulation and impairs fruit quality. The molecular mechanisms by which high temperature inhibits anthocyanin biosynthesis have yet to be fully elucidated. In this study, we demonstrated that MYBC2-L1 functions as a transcriptional repressor and its expression is strongly induced under high-temperature conditions. MYBC2-L1 represses anthocyanin synthesis by downregulating the transcription of key structural genes in the biosynthetic pathway of VvUFGT (UDP-glucose: flavonoid 3-O-glucosyltransferase) and VvLDOX (leucoanthocyanidin dioxygenase). Further biochemical assays revealed that MYBC2-L1 physically interacts with sucrose non-fermenting 1-related protein kinase 1α (SnRK1α), a negative regulator of anthocyanin accumulation. SnRK1α catalysers the phosphorylation of MYBC2-L1 at the Ser51 (S51) residue to modulate its biological activity. Collectively, we have identified a novel VvMYBC2L1-VvSnRK1α regulatory module that integrates abscisic acid (ABA) and heat signalling pathways, thereby synergistically suppressing anthocyanin accumulation in grape berries.