Metabolic and genetic analysis links <i>TRITERPENE SYNTHASE 12</i> to oleanolic acid biosynthesis in grape berry wax

Fruit surface cuticular waxes of grape berries are important in stress response and fruit quality. Despite extensive studies on the biosynthesis, regulation, and composition of fruit surface waxes, knowledge of the compositional variation and genetic mechanisms underlying grape berry cuticular wax formation remains limited. This study aimed to characterize grape berry cuticular wax composition and identify contributing genes. The wax composition of two grape cultivars ('Deckrot' and G1-7720) and their progeny shifted from aldehyde to fatty acid accumulation during ripening, while the composition was shown to influence Botrytis cinerea susceptibility. Alcohols and aldehydes contributed to the glaucous wax appearance, while the bioactive triterpene, oleanolic acid, was found to be the most abundant wax monomer. Metabolic quantitative trait locus analysis identified several genomic regions associated with wax monomer formation, including a cluster on chromosome 9 linked to triterpene content, which included eight putative triterpene synthases. Molecular phylogenetic analysis suggested that these genes code for amyrin synthases. Co-expression analysis, and subsequent heterologous expression in yeast, confirmed the involvement of VvTTPS12 in oleanolic acid formation. This study explores the role of grape berry wax composition and enhances understanding of genetic contributors to wax formation.