Catalyzes the transfer of D-xylose from UDP-alpha-D-xylose onto L-fucose. Probably involved in the biosynthesis of rhamnogalacturonan II (RG-II) through xylosylation of the internal fucose moiety of the A-chain of RG-II, a structurally complex pectic polysaccharide of the primary cell wall. RG-II is essential for the cell wall integrity of rapidly growing tissues such as roots and pollen tube growth and elongation. Widely expressed. The conserved DXD motif is involved in enzyme activity. Reduced fertility due to impaired growth of pollen tubes in the transmitting tract during fertilization. Belongs to the glycosyltransferase 77 family.