Novel Insights Into Glycan Fucosylation and Core Xylosylation in .

glycans carry plant typical β1,2-core xylose, α1,3-fucose residues, as well as plant atypical terminal β1,4-xylose and methylated mannoses. In a recent study, XylT1A was shown to act as core xylosyltransferase, whereby its action was of importance for an inhibition of excessive Man1A dependent trimming. Glycans found in a XylT1A/Man1A double mutant carried core xylose residues, suggesting the existence of a second core xylosyltransferase in . To further elucidate enzymes important for -glycosylation, novel single knockdown mutants of candidate genes involved in the -glycosylation pathway were characterized. In addition, double, triple, and quadruple mutants affecting already known -glycosylation pathway genes were generated. By characterizing -glycan compositions of intact -glycopeptides from these mutant strains by mass spectrometry, a candidate gene encoding for a second putative core xylosyltransferase (XylT1B) was identified. Additionally, the role of a putative fucosyltransferase was revealed. Mutant strains with knockdown of both xylosyltransferases and the fucosyltransferase resulted in the formation of glycans with strongly diminished core modifications. Thus, the mutant strains generated will pave the way for further investigations on how single glycan core epitopes modulate protein function in .