Identification of UGT85A glycosyltransferases associated with volatile conjugation in grapevine (Vitis vinifera x Vitis labrusca)

Glycosylated volatiles are considered as hidden aroma precursors that affect fruit flavor and are involved in plant defense response. Several uridine-diphosphate (UDP)-glycosyltransferase (UGT) members related to the glycosylation of volatiles have been identified from grapevine berries. Although grapevine leaves produced much higher levels of glycosylated volatiles than berries, UGTs responsible for the production of glycosylated volatiles in leaves have not yet been identified. Here, eight novel UGT genes were cloned, among these four members that belong to UGT85A family (named UGT85A24, UGT85A25, UGT85A26, and UGT85A27) were localized in the cytoplasm and their recombinant proteins showed activity toward volatiles detected in grapevine, with geraniol as the preferred substrate in vitro. Two UGT genes with 98.1% homology differ in R/S-linalool selection. The UGT85A26-catalyzed substrate showed enrichment in S-linalool, whereas UGT85A27 showed a strong preference for R-linalool. UGT85A24 and UGT85A25 were expressed mainly in berries, and UGT85A26 and UGT85A27 were expressed pre-dominantly in grapevine mature leaves and correlated with the highest content of glycosylated volatiles in the mature leaves. Methyl jasm-onate (MeJA) induced the expression of UGT85A26 and UGT85A27 as well as the production of linalyl-p-glucoside, citronellyl-p-glucoside and phenethyl-p-glucoside. Transient overexpression of UGT85A26 and UGT85A27 in tobacco leaves led to the accumulation of linalyl-p-glucoside and an increase in citronellyl-p-glucoside in vivo. These results indicate that the expression of UGT85A26 and UGT85A27 is a major regulator affecting the content of glycosylated volatiles in grapevine.