Processive glycosyltransferase involved in the biosynthesis of both the non-bilayer-prone beta-monoglycosyldiacylglycerol and the bilayer-forming membrane lipid beta-diglycosyldiacylglycerol. These components contribute to regulate the properties and stability of the membrane. Catalyzes sequentially the transfers of glucosyl or galactosyl residues from UDP-Glc or UDP-Gal to diacylglycerol (DAG) acceptor to form the corresponding beta-glycosyl-DAG (3-O-(beta-D-glycopyranosyl)-1,2-diacyl-sn-glycerol), which then acts as acceptor to give beta-diglycosyl-DAG product (3-O-(beta-D-glycopyranosyl-beta-(1->6)-D-glycopyranosyl)-1,2-diacyl-sn-glycerol). Dioleoylglycerol (DOG) is a preferred sugar acceptor than 3-O-(beta-D-glucopyranosyl)-1,2-dioleoyl-sn-glycerol. a 1,2-diacyl-sn-glycerol + UDP-alpha-D-glucose = a 1,2-diacyl-3-O-(beta-D-glucopyranosyl)-sn-glycerol + H(+) + UDP a 1,2-diacyl-sn-glycerol + UDP-alpha-D-galactose = a 1,2-diacyl-3-O-(beta-D-galactosyl)-sn-glycerol + H(+) + UDP a 1,2-diacyl-3-O-(beta-D-glucopyranosyl)-sn-glycerol + UDP-alpha-D-glucose = a 1,2-diacyl-3-O-(beta-D-Glc-(1->6)-beta-D-Glc)-sn-glycerol + H(+) + UDP a 1,2-diacyl-3-O-(beta-D-galactosyl)-sn-glycerol + UDP-alpha-D-galactose = a 1,2-diacyl-3-O-[beta-D-galactosyl-(1->6)-beta-D-galactosyl]-sn-glycerol + H(+) + UDP Activated by the negatively charged lipid dioleoylphosphatidylglycerol (DOPG) and inhibited by N-(n-nonyl)deoxygalactonojirimycin (C9J). kcat is 0.27 sec(-1) for Glc transfer with DOG as sugar acceptor. kcat is 1.10 sec(-1) for Gal transfer with DOG as sugar acceptor. kcat is 0.004 sec(-1) for Glc transfer with beta-glucosyl-DOG as sugar acceptor. kcat is 0.03 sec(-1) for Gal transfer with beta-glucosyl-DOG as sugar acceptor. Glycolipid metabolism; diglucosyl-diacylglycerol biosynthesis. The local lipid environment around the enzyme affects both the extent of head group elongation and total amounts of glycolipids produced. Belongs to the glycosyltransferase 2 family.