Catalyzes the reaction that attaches fucose through an O-glycosidic linkage to a conserved serine or threonine residue in the consensus sequence C1-X-X-S/T-C2 of thrombospondin type I repeats (TSRs) where C1 and C2 are the first and second cysteines of the repeat, respectively (PubMed:20637190). O-fucosylates members of several protein families including the ADAMTS, the thrombospondin (TSP) and spondin families (PubMed:20637190). Required for the proper secretion of ADAMTS family members such as ADAMTSL1 and ADAMTS13 (By similarity). The O-fucosylation of TSRs is also required for restricting epithelial to mesenchymal transition (EMT), maintaining the correct patterning of mesoderm and localization of the definite endoderm (PubMed:20637190). GDP-beta-L-fucose + L-seryl-[protein] = 3-O-(alpha-L-fucosyl)-L-seryl-[protein] + GDP + H(+) GDP-beta-L-fucose + L-threonyl-[protein] = 3-O-(alpha-L-fucosyl)-L-threonyl-[protein] + GDP + H(+) Protein modification; protein glycosylation. Mainly located in the endoplasmic reticulum. Null mice embryos die before 10.5 dpc. At the onset of gastrulation at 6.5 dpc, embryos are rounder and the embryonic and extra-embryonic ectoderm appears thickened and disorganized. Expression of NODAL and WNT3 is significantly expanded and/or displaced in the primitive streak as is BMP4 in the extra-embryonic ectoderm. By 7.5 dpc, embryos are unusually dense and shorter characterized by a dumb-bell appearance. There is unrestricted epithelial to mesenchymal transition (EMT) producing an abundance of mesenchymal cells. SNAIL1 expression is expanded and E-cadherin expression decreased. There is distal expansion of the proximal visceral endoderm. Belongs to the glycosyltransferase 68 family. Peptide-O-fucosyltransferase 2