Required for the formation of the callose wall separating the tetraspores (interstitial wall) and surrounding the pollen mother cells (peripheral wall). Required for exine formation on pollen wall. May be involved in callose synthesis during pollen tube growth. 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 Expressed throughout pollen development, both in pollen mother cells and in developing and mature pollen grains. Expressed in growing pollen tube. Plants develop deformed and inviable pollen grains which do not have exin. Belongs to the glycosyltransferase 48 family.