Essential protein. Glycosyltransferase that mediates the glycosylation of glycosylinositol phosphorylceramides (GIPCs), the major sphingolipids in the plasma membrane; acts as a HexN(Ac)-specific GIPC sugar transferase. Responsible for the glycosylation of a subgroup of GIPCs found in seeds and pollen that contain GlcNAc and GlcN (GlcN(Ac)). Maybe involved in the maintenance of cell-cell adhesion. Sphingolipid metabolism. Highly expressed in almost all tissues. Loss of the GlcN(Ac) glycosylinositol phosphorylceramides (GIPCs) is seedling lethal. Stunted plants when regenerated from callus. Belongs to the glycosyltransferase 64 family.