VvMYBC2-L1 cooperates with histone deacetylase VvHDA15 to repress anthocyanin biosynthesis in grape under high temperature

High temperature restricts anthocyanin accumulation in grape berries, but how transcriptional repressors coordinate with chromatin regulation remains unclear. We identified the MYB repressor VvMYBC2-L1 as a heat-responsive regulator through transcriptome analysis and functional assays. VvMYBC2-L1 overexpression reduced berry and callus pigmentation, anthocyanin accumulation, and expression of phenylpropanoid and anthocyanin biosynthetic genes. VvMYBC2-L1 associated with selected VvPAL and VvUFGT promoter regions, interacted with the basic helix-loop-helix protein VvMYC1, weakened the VvMYBA1–VvMYC1 interaction, and reduced their activation of both promoters. VvMYBC2-L1 also directly interacted with VvHDA15, a nuclear class II histone deacetylase with enzymatic activity in vitro. VvHDA15 overexpression repressed anthocyanin accumulation and reduced histone H3 lysine 9 acetylation at selected VvPAL and VvUFGT promoter regions. Conversely, VvHDA15 silencing partially restored berry coloration and anthocyanin accumulation under high temperature. Co-expression of VvMYBC2-L1 and VvHDA15 strengthened repression of anthocyanin accumulation and target-gene expression and further reduced histone acetylation at selected promoter regions relative to VvHDA15 overexpression alone. These findings identify functional cooperation between a heat-responsive MYB repressor and histone deacetylation that limits anthocyanin biosynthesis in grape berries.