A computational Study on Putative Anthocyanidin 3-O-glucosyltransferase genes from Vitis vinifera L. cv. Tannat Associated with Fruit Color Development
Anthocyanidin 3-O-glucosyltransferase (UFGT) is a key determinant of anthocyanin stabilization in grape berries. Understanding the molecular basis underlying the distinctive deep-purple pigmentation of Vitis vinifera L. cv. Tannat requires a detailed characterization of the genes encoding this enzyme and their products. Here, we combined comparative genomics, berry-skin expression profiling, sequence and phylogenetic analyses, mutual information mapping, structural modelling, and molecular dynamics (MD) simulations to identify and functionally characterize UFGT candidate genes associated with Tannat berry colour development. From an initial set of 300 genomic hits, seven loci were retained based on sequence features and expression patterns during berry skin pigmentation. These putative Tannat UFGT genes clustered into multiple pre-existing paralogous lineages, mapping mainly to chromosomes 16 and 18, supporting functional diversification rather than a recent lineage-specific expansion. Comparative structural analyses revealed a conserved C-terminal Rossmann-like core and a more variable N-terminal region enriched in substitutions and indels, consistent with differential acceptor recognition. Mutual information analysis further identified co-evolving residue networks linking both domains. Binding free energy estimates, computed using the MM/PBSA method, revealed gene-dependent ligand preferences toward the major Tannat anthocyanidins, driven primarily by non-polar interactions and polar solvation. In this context, the intense coloration of Tannat grapes is likely explained by the coordinated “division of labour” of UFGT genes at veraison, exhibiting favourable affinities for delphinidin and petunidin as acceptor aglycones, consistent with the abundance of their derived anthocyanin in the berry skin. Overall, the typical appearance of this cultivar is not only a trait of oenological importance but also an indicator of the strong antioxidant potential conferred by the accumulation of these bioactive metabolites.