Necessary for the synthesis of N-acetylglucosaminyl-phosphatidylinositol, the very early intermediate in GPI-anchor biosynthesis (Probable). Required for pollen germination and pollen tube growth (PubMed:14671020). a 1,2-diacyl-sn-glycero-3-phospho-(1D-myo-inositol) + UDP-N-acetyl-alpha-D-glucosamine = a 6-(N-acetyl-alpha-D-glucosaminyl)-1-phosphatidyl-1D-myo-inositol + H(+) + UDP Glycolipid biosynthesis; glycosylphosphatidylinositol-anchor biosynthesis. Expressed in roots, stems, leaves, flowers and pollen grains. Defective in pollen germination and pollen tube growth. Belongs to the glycosyltransferase group 1 family. Glycosyltransferase 4 subfamily.