Two pathogen-inducible UDP-glycosyltransferases, UGT73C3 and UGT73C4, catalyze the glycosylation of pinoresinol to promote plant immunity in Arabidopsis.

Abstract

UDP-glycosyltransferases (UGTs) constitute the largest glycosyltransferase family in the plant kingdom. They are responsible for transferring sugar moieties onto various small molecules to control many metabolic processes. However, their physiological significance in plants is largely unknown. Here, we revealed the function and mechanism of two Arabidopsis UGT genes, UGT73C3 and UGT73C4, which can be strongly induced by Pseudomonas syringae pv. tomato DC3000. Their overexpression significantly enhanced plant immune response, while the loss of their functions in double mutants resulted in the more sensitive phenotype to pathogen infection, although their single mutants had no obvious alteration in pathogen resistance. To understand the regulatory mechanism of UGT3C3/C4 in plant immunity, a completely secondary metabolome analysis and glycoside quantification were conducted. More accumulation of pinoresinol diglucosides was revealed in the UGT73C3 and UGT73C4 overexpression lines than that in wild-type plants whether before or after Pst DC3000 treatment, whereas the double mutants accumulated less pinoresinol diglucosides. Further, the in vitro and in vivo experiments demonstrated that UGT73C3 and UGT73C4 were capable of glycosylating pinoresinol to form pinoresinol monoglucoside and diglucoside. Moreover, we found that pinoresinol glycosylation promoted plant immune response by enhancing ROS production and callose deposition. Additionally, the transcriptional factor HB34 was identified to be responsible for the activation of UGT73C3 and UGT73C4 transcription and play a key role in plant immune responses. Overall, this study revealed a new pathway of plant immune responses via UGT73C3/C4 mediated pinoresinol glycosylation under the HB34 regulation.