Involved in pectin assembly and/or distribution, and in the synthesis of secondary wall glucuronoxylan. Probably involved in the synthesis of the glycosyl sequence at the glucuronoxylan reducing end. May be involved in synthesis of a complex glycan primer for xylan synthesis. Glycan metabolism; pectin biosynthesis. Highly expressed in stems. Detected in roots, inflorescences, siliques, and leaves. Expressed in cells undergoing secondary wall thickening, including interfascicular fibers and primary and secondary xylem. Severe dwarfing and seedling lethality. Collapsed xylem vessels. Reduced glucuronoxylan and homogalacturonan content in cell wall. Belongs to the glycosyltransferase 8 family.