Mutants in DEFECTIVE GLYCOSYLATION, an Arabidopsis homolog of an oligosaccharyltransferase complex subunit, show protein underglycosylation and defects in cell differentiation and growth

Abstract

A mutant called defective glycosylation1‐1 (dgl1‐1) was identified in Arabidopsis based on a growth defect of the dark‐grown hypocotyl and an abnormal composition of the non‐cellulosic cell wall polysaccharides. dgl1‐1 is altered in a protein ortholog of human OST48 or yeast WBP1, an essential protein subunit of the oligosaccharyltransferase (OST) complex, which is responsible for the transfer in the ER of the N‐linked glycan precursor onto Asn residues of candidate proteins. Consistent with the known function of the OST complex in eukaryotes, the dgl1‐1 mutation led to a reduced N‐linked glycosylation of the ER‐resident protein disulfide isomerase. A second more severe mutant (dgl1‐2) was embryo‐lethal. Microscopic analysis of dgl1‐1 revealed developmental defects including reduced cell elongation and the collapse and differentiation defects of cells in the central cylinder. These defects were accompanied by changes in the non‐cellulosic polysaccharide composition, including the accumulation of ectopic callose. Interestingly, in contrast to other dwarf mutants that are altered in early steps of the N‐glycan processing, dgl1‐1 did not exhibit a cellulose deficiency. Together, these results confirm the role of DGL1 in N‐linked glycosylation, cell growth and differentiation in plants.