Genome-wide identification of the UGT gene family revealing PbUGT73EC3 participating in drought stress in Phoebe bournei

Drought stress significantly limits plant growth and development, and previous studies have demonstrated that glycosyltransferases play crucial roles in stress responses. However, the mechanisms by which UGT genes confer drought tolerance in Phoebe bournei remain largely unknown. In this study, a total of 151 PbUGT genes were identified and systematically named. Phylogenetic analysis classified these genes into 22 subfamilies, all of which contain the conserved PSPG box. Cis-element analysis identified a large number of stress-responsive elements in the promoters of PbUGT members. Combined transcriptomic and RT-qPCR analyses showed that the majority of members from the UGT73, UGT74, UGT85, UGT89, and UGT707 subfamilies were highly expressed under PEG-induced drought conditions. Moreover, nine candidate genes exhibited significant transcriptional responses to drought stress. PbUGT73EC3, in particular, was selected for functional validation. In all three transgenic systems, its overexpression significantly increased the accumulation of kaempferol-3-O-rutinoside. The PbUGT73EC3-overexpressing lines displayed enhanced drought tolerance, with increased flavonoid content, elevated activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT), and reduced levels of malondialdehyde (MDA), hydrogen peroxide (H₂O₂), and leaf water loss rate. These results suggest that PbUGT73EC3 may enhance plant drought tolerance by regulating the biosynthesis of kaempferol-3-O-rutinoside and promoting the scavenging of reactive oxygen species (ROS) through glycosylation. In summary, these findings provide a comprehensive characterization of the UGT gene family in P. bournei and elucidate their potential roles in drought stress responses, offering a theoretical basis for molecular breeding aimed at improving drought tolerance and for further functional studies of UGT genes.