Involved in callose synthesis at the forming cell plate during cytokinesis. Not required for callose formation after wounding or pathogen attack. During plant growth and development, callose is found as a transitory component of the cell plate in dividing cells, is a major component of pollen mother cell walls and pollen tubes, and is found as a structural component of plasmodesmatal canals. [(1->3)-beta-D-glucosyl](n) + UDP-alpha-D-glucose = [(1->3)-beta-D-glucosyl](n+1) + H(+) + UDP May be regulated by ROP1 through the interaction with UGT1. Interacts with UGT1 and phragmoplastin. May form a functional complex with UGT1, ROP1 and phragmoplastin. Localized in the forming cell plate during cytokinesis. A number of isoforms are produced. According to EST sequences. Belongs to the glycosyltransferase 48 family.