N-Glycosylation Process in Both ER and Golgi Plays Pivotal Role in Plant Immunity

N-glycosylation of proteins in the endoplasmic reticulum (ER) and Golgi apparatus is essential for protein posttranslational modification in plant cells. Although the N-glycosylation in the ER and Golgi apparatus has been known to regulate protein quality control, salt stress and cellulose biosynthesis, few evidences related to the roles of Nglycosylation in plant immunity have been reported. Arabidopsis thaliana mutants defective in N-glycosylation, namely, staurosporin and temperature sensitive 3a and 3b (stt3a and stt3b) of oligosaccharyltransferase subunit and complex glycan 1 (cgl1) in Golgi apparatus were used in this study. Results showed that Arabidopsis mutant stt3a was more susceptible against Pseudomonas syringae pv. tomato DC3000 (Pst) and Erwinia carotovora subsp. carotovora (ECC). In addition, stt3a was less resistant against Pst harboring effector protein AvrRpm1 compared to the wild type plant. However stt3b showed less significant changes in susceptibility against these three bacterial strains. These results infer the functions of STT3B in N-glycosylation that STT3B is likely supplementary to the main STT3A. Flg22-induced PR1 accumulation and callose deposition were blocked in N-glycosylation mutants, implying that N-glycosylation is involved in the PAMP-triggered immunity. However, N-glycosylation was not absolutely required for AvrRpm1- and AvrRpt2-triggered immunity. STT3A-binding proteins were searched in order to understand the role of STT3A in plant immunity. Ubiquitin-conjugating enzyme E2s, UBC7 and UBC13, were found to be binding proteins of STT3A by yeast two-hybrid assay.