OsMOGS Is Required For N-glycan Formation And Auxin-Mediated Root Development In Rice(Oryza Sativa)

Glycoprotein, a biomacromolecule widely existing in eukaryotic cells, is a modified protein that oligosaccharide chains covalently attached to polypeptide side-chains. N-glycosylation is a major modification of glycoproteins, so the oligosaccharide chain part is referred to as N-glycan. Recently, identification and functional analytris of key enzyme coding genes involved in the pathway of N-glycan production in plants is an important aspect of glycobiology. In the present study, we isolated a rice mutant displaying shortened root from an EMS-derived mutant library. Map-based cloning revealed that the mutated gene locus occurred at LOC_Os01g69210, with a C to A point mutation at224bp of ORF, resulting in an Ala75to Asp75transition in the predicted protein. The gene codes a putative mannosyl-oligosaccharide glucosidase (MOGS), a GCS1ortholog in Arabidopsis, which belongs to glycohydrolase family63(GH63). MOGS acts in removal of the terminal glucose residue of oligosaccharide chain which is transferred from ER lipid dolichol (Dol) to nascent peptide. The evidence that two independent OsMOGS-knockout mutant lines caused by T-DNA insertion mimicked the osmogs mutant, and introduction of full length OsMOGS cDNA into osmogs fully complemented the root defect, confirms that OsMOGS is involved in root development. Phenotypical and physiological analysis of osmogs mutant were performed in detail, and the results were summarized as follows:(1) Arrested root growth-promoter of OsCYCB1;1, a cell cycle marker gene fused a GUS reporter showed in osmogs mutant, initiation of lateral root primordial was nomal, but elongation was suppressed, as well, elongation region was shortened and mitotic activity of meristem region was declined, the results were consistent with these of longitudinal section in root tip.(2) Abnormal root epidermis-in mutant, the root epidemical cell of mature region was enlarged and bulged, but cell wall was thinned, the results demonstrated that deficiency of N-glycan interrupted cellulose synthesis and cell wall formation, leading to abnormal growth of epidermis and root hair.(3) Attenuation of auxin signaling-compared to WT, auxin response genes in mutant root were less induced by exogenous auxin; DR5::GUS staining showed that auxin signaling was inpaired, and decreased auxin content and polar transport conferred insensitivity of mutant root to auxin.(4) Restoration of root growth by sugar-induce auxin-application of soluble sugar (sucrose or glucose) on MS media, in mutant root expression of genes which code key enzyme of auxin biosynthesis was increased and the content of IAA was elevated, so the deficiency of auxin in mutant root was offset by sugar-induce auxin biosynthesis, and the growth of mutant root was restored.In summary, involvement of OsMOGS in N-glycan biosynthesis is required for auxin polar transport mediated establishment of root auxin gradient and root development.