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 and accepts glucosamine (GlcN) and N-acetylglucosamine (GlcNAc) as the sugar unit (PubMed:29760197). Responsible for the glycosylation of a subgroup of GIPCs found in seeds and pollen that contain GlcNAc and GlcN (GlcN(Ac)) (PubMed:29760197). Maybe involved in the maintenance of cell-cell adhesion (PubMed:29760197). a 1,2-diacyl-sn-glycero-3-phospho-(1D-myo-inositol) + an N-(2R-hydroxy-very-long-chain fatty acyl)-(R)-4-hydroxysphingoid base = a 1,2-diacyl-sn-glycerol + a 1D-myo-inositol-1-phospho-N-[(R)-2-hydroxy-very-long-chain fatty acyl]-(R)-4-hydroxysphingoid base Sphingolipid metabolism. Specifically and highly expressed in developing embryos and mature seeds. Also detected at low levels in stigma and pollen. Highly expressed in dry seed but drastically down-regulated after seed imbibition. Loss of the GlcN(Ac) glycosylinositol phosphorylceramides (GIPCs) leading to a reduced sensitivity to abiotic stress (e.g. abscisic acid and salt) on seed germination. Reduced HexNAc-GIPC content. Slightly larger seeds with more seed storage lipids and proteins and larger seed coat cells. Belongs to the glycosyltransferase 64 family. Truncated N-terminus.