Glycosyletransferase required for the proper composition and structural properties of released seed coat mucilage (PubMed:11706181, PubMed:26482889, PubMed:26979331). Required for the production of highly branched xylan polymers in seed coat mucilage (PubMed:26482889). Facilitates the addition of xylose residues directly to the xylan backbone (PubMed:26482889, PubMed:26979331). Xylan with xylose side chains seems to be necessary for pectin attachment to the seed surface (PubMed:26482889, PubMed:26979331). Essential for xylan synthesis in seed coat epidermal (SCE) cells (PubMed:26482889). Expressed in the seed coat at the linear cotyledon and mature green stages, when mucilage synthesis occurs. Reduced amount and altered composition of seed coat mucilage. Belongs to the glycosyltransferase 61 family.