Integrated omics identifies VviGTs and VviMYB174 as drivers of glycosylated monoterpenoid accumulation in 'Ruiduhongyu' grapes.

Abstract

Monoterpenoids contribute to grape and wine varietal aroma as free volatiles and glycosidically bound precursors. While glycosylated forms largely determine postharvest aroma potential, the genes controlling their accumulation remain largely unidentified. Here, we compared free and glycosylated monoterpenoids and the accompanying transcriptome between the green-skinned 'Ruiduxiangyu' (RDXY) and the pink-skinned 'Ruiduhongyu' (RDHY), two siblings derived from the same cross. RDHY berries accumulated higher levels of glycosylated monoterpenoids during ripening, whereas RDXY berries were enriched in the free forms. Integrated metabolome-transcriptome analysis revealed a tight correlation between glycosylated monoterpenoid content and the expression of five glycosyltransferase (GT) genes (VviGTs) and the transcription factor VviMYB174. Besides the previously characterized VviGT14 and VviGT7, enzyme activity assay and transient overexpression experiments in tobacco leaves, grape leaves, and grape berries demonstrated that VviGT22, VviGT37, and VviGT74 also possess monoterpenol glycosylation activity. Yeast one-hybrid assays, combined with overexpression and silencing analyses, confirmed that VviMYB174 directly upregulates these three GT genes in RDHY, thereby promoting glycosylated monoterpenoid accumulation. Sequence alignment revealed that only VviGT74 exhibited different promoter sequence divergence between the two cultivars, notably, the VviGT74 promoter from RDXY failed to bind VviMYB174, which correlated with its reduced expression in RDXY berries. These findings provide new targets for manipulating the glycosylated aroma precursor pool and advance the molecular understanding of monoterpenoid metabolism in grapevine.