A Predominant Role of AtEDEM1 in Catalyzing a Rate-Limiting Demannosylation Step of an Arabidopsis Endoplasmic Reticulum-Associated Degradation Process

Jianjun Zhang; Yang Xia; Dinghe Wang; Yamin Du; Yongwu Chen; Congcong Zhang; Juan Mao; Muyang Wang; Yi-Min She; Xinxiang Peng; Li Liu; Josef Voglmeir; Zuhua He; Linchuan Liu; Jianming Li

doi:10.3389/fpls.2022.952246

A Predominant Role of AtEDEM1 in Catalyzing a Rate-Limiting Demannosylation Step of an Arabidopsis Endoplasmic Reticulum-Associated Degradation Process

Front Plant Sci. 2022 Jul 7:13:952246. doi: 10.3389/fpls.2022.952246. eCollection 2022.

Authors

Jianjun Zhang^{1

2

3}, Yang Xia³, Dinghe Wang^{4

5}, Yamin Du⁶, Yongwu Chen^{4

5}, Congcong Zhang^{4

5}, Juan Mao^{1

2}, Muyang Wang⁵, Yi-Min She⁵, Xinxiang Peng¹, Li Liu⁶, Josef Voglmeir⁶, Zuhua He⁵, Linchuan Liu^{1

2}, Jianming Li^{1

2

3}

Affiliations

¹ State Key Laboratory for Conservation and Utilization of Subtropical Agro-Bioresources, South China Agricultural University, Guangzhou, China.
² Guangdong Key Laboratory for Innovative Development and Utilization of Forest Plant Germplasm, College of Forestry and Landscape Architecture, South China Agricultural University, Guangzhou, China.
³ Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, MI, United States.
⁴ University of Chinese Academy of Sciences, Beijing, China.
⁵ The Center of Excellence for Molecular Plant Sciences, Chinese Academy of Sciences, Shanghai, China.
⁶ Glycomics and Glycan Bioengineering Research Center, College of Food Science and Technology, Nanjing Agricultural University, Nanjing, China.

Abstract

Endoplasmic reticulum-associated degradation (ERAD) is a key cellular process for degrading misfolded proteins. It was well known that an asparagine (N)-linked glycan containing a free α1,6-mannose residue is a critical ERAD signal created by Homologous to α-mannosidase 1 (Htm1) in yeast and ER-Degradation Enhancing α-Mannosidase-like proteins (EDEMs) in mammals. An earlier study suggested that two Arabidopsis homologs of Htm1/EDEMs function redundantly in generating such a conserved N-glycan signal. Here we report that the Arabidopsis irb1 (reversal of bri1) mutants accumulate brassinosteroid-insensitive 1-5 (bri1-5), an ER-retained mutant variant of the brassinosteroid receptor BRI1 and are defective in one of the Arabidopsis Htm1/EDEM homologs, AtEDEM1. We show that the wild-type AtEDEM1, but not its catalytically inactive mutant, rescues irb1-1. Importantly, an insertional mutation of the Arabidopsis Asparagine-Linked Glycosylation 3 (ALG3), which causes N-linked glycosylation with truncated glycans carrying a different free α1,6-mannose residue, completely nullifies the inhibitory effect of irb1-1 on bri1-5 ERAD. Interestingly, an insertional mutation in AtEDEM2, the other Htm1/EDEM homolog, has no detectable effect on bri1-5 ERAD; however, it enhances the inhibitory effect of irb1-1 on bri1-5 degradation. Moreover, AtEDEM2 transgenes rescued the irb1-1 mutation with lower efficacy than AtEDEM1. Simultaneous elimination of AtEDEM1 and AtEDEM2 completely blocks generation of α1,6-mannose-exposed N-glycans on bri1-5, while overexpression of either AtEDEM1 or AtEDEM2 stimulates bri1-5 ERAD and enhances the bri1-5 dwarfism. We concluded that, despite its functional redundancy with AtEDEM2, AtEDEM1 plays a predominant role in promoting bri1-5 degradation.

Keywords: BRASSINOSTEROID-INSENSITIVE 1; N-glycan; endoplasmic reticulum-associated degradation; protein degradation; α1,2-mannosidase; α1,6-mannose residue.