Galactosyltransferase involved in the biosynthesis of type II arabinogalactan. Possesses galactosyltransferase (GalT) activity in vitro, transferring galactose from UDP-galactose to a mixture of various oligosaccharides derived from arabinogalactan proteins. Forms a complex with GALT31A that can work cooperatively to enhance the activities of adding galactose residues at O6 positions to beta-1,6-galactan and beta-1,3-galactan. Interacts with GALT31A. Belongs to the glycosyltransferase 29 family.