UGT85A53 promotes flowering via mediating abscisic acid glucosylation and FLC transcript in Camellia sinensis

Uridine-diphosphate dependent glycosyltransferases catalyse the glycosylation of small molecules and play an important role in maintaining cell homeostasis and regulating plant development. Glycosyltransferases are widely distributed, but their biological roles in regulating plant growth and development are largely unknown. In this study, we identified a UDP-glycosyltransferase CsUGT85A53 from Camellia sinensis, whose expression is strongly induced by various abiotic stress factors and its protein product distributed in both cytoplasm and nucleus. Ectopically over-expression of CsUGT85A53 in Arabidopsis resulted in an early flowering phenotype under both long-day and short-day conditions. The transcript accumulation of the flowering repressor genes FLC and ABI5, an activator of FLC in ABA-regulated flowering signaling, are all significantly repressed in transgenic Arabidopsis compared with wild-type plants. The decreased expression level of FLC gene might be associated with its increased DNA methylation level in CsUGT85A53-OE plants. Biochemical analyses show that CsUGT85A53 could glucosylate ABA to form inactive ABA-glycoside in vitro and in planta. Over-expression of CsUGT85A53 in Arabidopsis resulted in a decreased level of free ABA and increased level of ABA-glucoside. The early flowering phenotype in the CsUGT85A53-OE transgenic lines were restored due to ABA application. Further, CsUGT85A53 overexpressed plants displayed ABA-insensitive phenotype with higher germination rates compared with control in the presence of lower concentrations of exogenous ABA. Our findings revealed the first UGT in tea plants catalyzing ABA glucosylation and enhancing flowering transition as a positive regulator.