Identification of the Gene Encoding the 1,3-Mannosyltransferase (ALG3) in Arabidopsis and Characterization of Downstream N-Glycan Processing[W].

M.G.L. Henquet, L. Lehle, M.E.L. Schreuder, G.J.A. Rouwendal, J.W. Molthoff, J.P.F.G. Helsper, A.R. van der Krol, H.J. Bosch

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Abstract

Glycosyltransferases are involved in the biosynthesis of lipid-linked N-glycans. Here, we identify and characterize a mannosyltransferase gene from Arabidopsis thaliana, which is the functional homolog of the ALG3 (Dol-P-Man: Man(5)GlcNAc(2)-PP-Dol alpha 1,3-mannosyl transferase) gene in yeast. The At ALG3 protein can complement a Delta alg3 yeast mutant and is localized to the endoplasmic reticulum in yeast and in plants. A homozygous T-DNA insertion mutant, alg3-2, was identified in Arabidopsis with residual levels of wild-type ALG3, derived from incidental splicing of the 11th intron carrying the T-DNAs. N- glycan analysis of alg3-2 and alg3-2 in the complex-glycan-less mutant background, which lacks N- acetylglucosaminyl-transferase I activity, reveals that when ALG3 activity is strongly reduced, almost all N-glycans transferred to proteins are aberrant, indicating that the Arabidopsis oligosaccharide transferase complex is remarkably substrate tolerant. In alg3-2 plants, the aberrant glycans on glycoproteins are recognized by endogenous mannosidase I and N- acetylglucosaminyltransferase I and efficiently processed into complex-type glycans. Although no high-mannose-type glycoproteins are detected in alg3-2 plants, these plants do not show a growth phenotype under normal growth conditions. However, the glycosylation abnormalities result in activation of marker genes diagnostic of the unfolded protein response.
Original languageEnglish
Pages (from-to)1652-1664
JournalThe Plant Cell
Volume20
Issue number6
DOIs
Publication statusPublished - 2008

Keywords

  • asparagine-linked oligosaccharides
  • deficient glycoprotein syndrome
  • unfolded protein response
  • yeast mutants deficient
  • endoplasmic-reticulum
  • saccharomyces-cerevisiae
  • congenital disorder
  • oligosaccharyltransferase complex
  • acetylglucosaminyltransferase

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