Arabidopsis glucosidase I mutants reveal a critical role of N-glycan trimming in seed development

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Abstract
Glycoproteins with asparagine‐linked (N‐linked) glycans occur in all eukaryotic cells. The function of their glycan moieties is one of the central problems in contemporary cell biology. N‐glycosylation may modify physicochemical and biological protein properties such as conformation, degradation, intracellular sorting or secretion. We have isolated and characterized two allelic Arabidopsis mutants, gcs1‐1 and gcs1‐2 , which produce abnormal shrunken seeds, blocked at the heart stage of development. The mutant seeds accumulate a low level of storage proteins, have no typical protein bodies, display abnormal cell enlargement and show occasional cell wall disruptions. The mutated gene has been cloned by T‐DNA tagging. It codes for a protein homologous to animal and yeast α‐glucosidase I, an enzyme that controls the first committed step for N ‐glycan trimming. Biochemical analyses have confirmed that trimming of the α1,2‐ linked glucosyl residue constitutive of the N ‐glycan precursor is blocked in this mutant. These results demonstrate the importance of N ‐glycan trimming for the accumulation of seed storage proteins, the formation of protein bodies, cell differentiation and embryo development.