Probable xyloglucan xylosyltransferase involved in the biosynthesis of xyloglucan in roots. May act in association with XXT1 and XXT2 (PubMed:18557833). Associates with other xyloglucan-synthesizing enzymes to form multiprotein complexes for xyloglucan synthesis in the Golgi (PubMed:25392066). Transfers an alpha-D-xylosyl residue from UDP-D-xylose to a glucose residue in xyloglucan, forming an alpha-(1->6)-D-xylosyl-D-glucose linkage. Interacts with XXT2 and CSLC4 (PubMed:22665445). Interacts with FUT1 and XLT2 (PubMed:25392066). Highly expressed in roots, stems and cauline leaves, and at lower levels in rosette leaves, flowers and siliques. Root hair phenotype, characterized by short root hairs with bubble-like extrusions at the tip. Alteration of the main root cellular morphology. Reduced xyloglucan content. Belongs to the glycosyltransferase 34 family.