-acetylglucosaminyltransferase II Is Involved in Plant Growth and Development Under Stress Conditions.

Alpha-1,6-mannosyl-glycoprotein 2-β--acetylglucosaminyltransferase [EC 2.4.1.143, -acetylglucosaminyltransferase II (GnTII)] catalyzes the transfer of N-acetylglucosamine (GlcNAc) residue from the nucleotide sugar donor UDP-GlcNAc to the α1,6-mannose residue of the di-antennary N-glycan acceptor GlcNAc(Xyl)Man(Fuc)GlcNAc in the Golgi apparatus. Although the formation of the GlcNAc(Xyl)Man(Fuc)GlcNAc N-glycan is known to be associated with GnTII activity in , its physiological significance is still not fully understood in plants. To address the physiological importance of the GlcNAc(Xyl)Man(Fuc)GlcNAc N-glycan, we examined the phenotypic effects of loss-of-function mutations in in the presence and absence of stress, and responsiveness to phytohormones. Prolonged stress induced by tunicamycin (TM) or sodium chloride (NaCl) treatment increased expression in wild-type Arabidopsis (ecotype Col-0) but caused severe developmental damage in GnTII loss-of-function mutants ( and ). The absence of the 6-arm GlcNAc residue in the N-glycans in facilitated the TM-induced unfolded protein response, accelerated dark-induced leaf senescence, and reduced cytokinin signaling, as well as susceptibility to cytokinin-induced root growth inhibition. Furthermore, and seedlings exhibited enhanced N-1-naphthylphthalamic acid-induced inhibition of tropic growth and development. Thus, GnTII's promotion of the 6-arm GlcNAc addition to N-glycans is important for plant growth and development under stress conditions, possibly affecting glycoprotein folding and/or distribution.