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

Yang Jae Kang,Jae Yong Yoo,Young Eun Lee,Ki Seong Ko,Seok Han Yoon,Thao Thi Pham,Kyun Oh Lee,Bich Ngoc Vu,Jong Chan Hong,Ji-Yeon Kim,Jae-Min Lim

doi:10.3389/fpls.2021.761064

Yang Jae Kang, Jae Yong Yoo + Show 9 more

Open Access

https://doi.org/10.3389/fpls.2021.761064

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Abstract

Alpha-1,6-mannosyl-glycoprotein 2-β-N-acetylglucosaminyltransferase [EC 2.4.1.143, N-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)Man3(Fuc)GlcNAc2 in the Golgi apparatus. Although the formation of the GlcNAc2(Xyl)Man3(Fuc)GlcNAc2 N-glycan is known to be associated with GnTII activity in Arabidopsis thaliana, its physiological significance is still not fully understood in plants. To address the physiological importance of the GlcNAc2(Xyl)Man3(Fuc)GlcNAc2 N-glycan, we examined the phenotypic effects of loss-of-function mutations in GnTII in the presence and absence of stress, and responsiveness to phytohormones. Prolonged stress induced by tunicamycin (TM) or sodium chloride (NaCl) treatment increased GnTII expression in wild-type Arabidopsis (ecotype Col-0) but caused severe developmental damage in GnTII loss-of-function mutants (gnt2-1 and gnt2-2). The absence of the 6-arm GlcNAc residue in the N-glycans in gnt2-1 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, gnt2-1 and gnt2-2 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 via affecting glycoprotein folding and/or distribution.

Highlights

Proteins destined for secretion or incorporation into cellular membranes are initially transferred into the endoplasmic reticulum (ER) as they are being translated on membrane-bound ribosomes (Gomord and Faye, 2004; Walsh, 2010)
We treated Col-0 plants with either mass spectrometry (MS) medium or MS medium supplemented with NaCl or TM and analyzed GnTII transcription by Quantitative PCR (qPCR) to investigate how it might be altered under stress conditions
While GnTII transcription did not increase in response to short-term stress, we found that it did increase in response to prolonged stress (Figure 1A)

Summary

INTRODUCTION

Proteins destined for secretion or incorporation into cellular membranes are initially transferred into the endoplasmic reticulum (ER) as they are being translated on membrane-bound ribosomes (Gomord and Faye, 2004; Walsh, 2010). The GlcNAcMan3GlcNAc2 structure produced by N-acetylgl ucosaminyltransferase I (GnTI) and Golgi α-mannosidase II (GMII) in the plant Golgi serves as a common acceptor of GlcNAc, xylose, and fucose residues through the activities of N-acetylglucosaminyltransferase II (GnTII), β1,2-xylosyl transferase (XylT), and α1,3-fucosyltransferase (FucT), respectively (Kang et al, 2008; Schoberer and Strasser, 2011; Yoo et al, 2015). Both limited addition of the 6-arm GlcNAc residue by GnTII and processing of the 3-arm GlcNAc residue by β-N-acetylhexosaminidases (HEXOI, II, and III) facilitate formation of the paucimannose N-glycan [(Xyl)Man3(Fuc) GlcNAc2] in plants (Liebminger et al, 2011; Yoo et al, 2015). We analyzed the distinctive phenotypes of the gnt and gnt plants in response to stresses and phytohormones to gain insight into the physiological functions of the minor N-glycan in plants

RESULTS

DISCUSSION

EXPERIMENTAL PROCEDURES