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

Glycoproteins with asparagine-linked (N-linked) glycans occur in all eukary otic cells, The function of their glycan moieties is one of the central pro blems in contemporary cell biology. N-glycosylation may modify physicochemi cal and biological protein properties such as conformation, degradation, in tracellular sorting or secretion. We have isolated and characterized two al lelic Arabidopsis mutants, gcs1-1 and gcs1-2, which produce abnormal shrunk en seeds, blocked at the heart stage of development. The mutant seeds accum ulate a low level of storage proteins, have no typical protein bodies, disp lay abnormal cell enlargement and show occasional cell wall disruptions, Th e mutated gene has been cloned by T-DNA tagging. It codes for a protein hom ologous to animal and yeast alpha -glucosidase I, an enzyme that controls t he first committed step for N-glycan trimming, Biochemical analyses have co nfirmed that trimming of the alpha1,2linked glucosyl residue constitutive o f the N-glycan precursor is blocked in this mutant, These results demonstra te the importance of N-glycan trimming for the accumulation of seed storage proteins, the formation of protein bodies, cell differentiation and embryo development.