Characterization of triterpenoid profiles and triterpene synthase expression in the leaves of eight Vitis vinifera cultivars grown in the Upper Rhine Valley

Plant triterpenoids are a diverse group of secondary metabolites with wide distribution, high chemical diversity and interesting pharmacological and antimicrobial properties. The first step in the biosynthesis of all triterpenoids is the cyclization of the 2,3-oxidosqualene precursor, catalyzed by oxidosqualene cyclases (OSCs), which have characteristic product specificities. Biosynthesis and functions of pentacyclic triterpenes have been poorly studied in grapevine. In this study, we first investigated the profile of triterpenoids present in leaf cuticular waxes from eight Vitis vinifera cultivars cultivated in the Upper Rhine Valley. Further quantification of triterpenoids showed that these cultivars can be divided into two groups, characterized by high levels of lupeol (e.g., Pinot noir) or taraxerol (e.g., Gewurztraminer) respectively. We further analyzed the OSC family involved in the synthesis of pentacyclic triterpenes (called VvTTPSs) in the sequenced V. vinifera 40024 genome and found nine genes with similarity to previously characterized triterpene synthases. Phylogenetic analysis further showed that VvTTPS1-VvTTPS3 and VvTTPS5-VvTTPS9 belong to the beta-amyrin synthase and multifunctional triterpene synthase clade, whereas VvTTPS10 belongs to the lupeol synthase clade. We studied the expression of several members of the VvTTPS family following biotic and abiotic stresses in V. vinifera 40024 as well as in the eight healthy cultivars. This study further revealed that one candidate gene, VvTTPS5, which does not belong to the lupeol synthase clade, is highly expressed in lupeol-rich cultivars. VvTTPS3, VvTTPS5, VvTTPS6, VvTTPS7 and VvTTPS10 were highly upregulated by UV stress, but only VvTTPS3, VvTTPS5, VvTTPS6 and VvTTPS10 were upregulated following downy mildew and gray mold infections respectively. These results suggest differential roles of VvTTPS against environmental stresses in grape leaves.