Galactosyltransferase synthesizing digalactosyldiacylglycerol from monogalactosyldiacylglycerol in the absence of UDP-galactose (By similarity). Potentially involved in freezing tolerance (PubMed:18466306). 2 a 1,2-diacyl-3-O-(beta-D-galactosyl)-sn-glycerol = a 1,2-diacyl-3-O-[beta-D-galactosyl-(1->6)-beta-D-galactosyl]-sn-glycerol + a 1,2-diacyl-sn-glycerol Rice SFR2 is able to rescue freezing tolerance phenotype in Arabidopsis sfr2 mutant. Belongs to the glycosyl hydrolase 1 family.