Plays a role in the arabinosylation of cell wall components. Involved in the arabinosylation of extensin proteins in root hair cells (PubMed:19667208, PubMed:21680836). Extensins are structural glycoproteins present in cell walls and its arabinosylation is important for cell elongation, root hair cell development, lateral root development and root hair tip growth (PubMed:19667208, PubMed:21680836, PubMed:24619997, PubMed:25944827). The conserved DXD motif is involved in enzyme activity. Increased elongation of hypocotyls (PubMed:19667208). Reduced root hair length (PubMed:21680836). Reduced content of arabinosylated extensins in cell walls (PubMed:19667208, PubMed:21680836). Increased lateral root formation (PubMed:24619997). Belongs to the glycosyltransferase 77 family.