Integrated transcriptomic and metabolomic analysis of shading effects on berry quality and anthocyanin synthesis in wine grape 'Marselan'.

Anthocyanins are core light-regulated pigments determining grape berry color. This study aimed to determine how shading applied at different post-bloom stages affects berry quality, veraison, anthocyanin composition, and associated transcriptional responses in 'Marselan' grapevines. Three treatments were established, including two shading regimes at 15 (T1) and 57 days (T2) after full bloom and a natural light control (CK). Shading delayed veraison and extended its duration, with T1 showing the most pronounced effects on increasing soluble solids and reducing titratable acidity. DEGs enriched the flavonoid biosynthesis pathway, and WGCNA revealed the specific regulatory roles of distinct co-expression modules in response to shading during berry coloration. Metabolomics detected 29 anthocyanin components, whose composition and content were significantly altered by shading timing. Correlation analysis identified HCT (VIT_11s0037g00440) and ANR (VIT_19s0014g04980) as genes associated with multiple anthocyanins, while expression patterns of UGT75C1, UGT79B1 and BZ1 were consistent with treatment-dependent changes in anthocyanin profiles.