Mannosyltransferase involved in glycosylphosphatidylinositol-anchor biosynthesis (PubMed:24963069). Required for the pollen tube micropylar guidance and embryo development by regulating GPI-anchor mediated protein localization (e.g. COBL10 and A36) (PubMed:24963069, PubMed:27872247). Mostly expressed, mainly in vascular tissues, in leaves, roots, stems, flowers, siliques and pollen, and, to a lower extent, in seedlings. Expressed in vascular tissue of seedlings, leaves, root tips, inflorescence stems and flowers (PubMed:24963069). In pistils, detected in the ovary walls, styles, mature embryo sacs and developing embryos (PubMed:24963069). In pollen grains, mostly present in mature grains at anthesis and in germinated pollen tubes (PubMed:24963069). Embryo lethality at the globular or earlier stages (PubMed:24963069). Compromised pollen tubes micropylar guidance, but normal pollen germination and tube growth, associated with an abnormal localization of GPI-anchored proteins (e.g. COBL10) (PubMed:24963069). Impaired apical plasma membrane localization of COBL10 in pollen tubes, important for the growth of pollen tubes in the transmitting tract of pistil (PubMed:24963069). Lost A36 plasma membrane and cytoplasmic punctate localization which displays a constitutive reticular localization (PubMed:27872247). Belongs to the glycosyltransferase 22 family.