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Identification of a Xylogalacturonan Xylosyltransferase Involved in Pectin Biosynthesis in Arabidopsis^[W],[OA]

^a Laboratory of Molecular Plant Biology, Department of Plant Biology, Faculty of Life Sciences, University of Copenhagen, DK-1871 Frederiksberg C, Denmark
^b Department of Molecular Biology, Faculty of Science, University of Copenhagen, DK-1353 Copenhagen, Denmark
^c Laboratory of Food Chemistry, Department of Agrotechnology and Food Sciences, Wageningen University, 6700 EV Wageningen, The Netherlands
^d Max Planck Institute for Molecular Plant Physiology, D-14476 Golm, Germany
^e Feedstocks Division, Joint Bioenergy Institute, Emeryville, California 94608

¹ Address correspondence to hscheller{at}lbl.gov.

Xylogalacturonan (XGA) is a class of pectic polysaccharide found in plant cell walls. The Arabidopsis thaliana locus At5g33290 encodes a predicted Type II membrane protein, and insertion mutants of the At5g33290 locus had decreased cell wall xylose. Immunological studies, enzymatic extraction of polysaccharides, monosaccharide linkage analysis, and oligosaccharide mass profiling were employed to identify the affected cell wall polymer. Pectic XGA was reduced to much lower levels in mutant than in wild-type leaves, indicating a role of At5g33290 in XGA biosynthesis. The mutated gene was designated xylogalacturonan deficient1 (xgd1). Transformation of the xgd1-1 mutant with the wild-type gene restored XGA to wild-type levels. XGD1 protein heterologously expressed in Nicotiana benthamiana catalyzed the transfer of xylose from UDP-xylose onto oligogalacturonides and endogenous acceptors. The products formed could be hydrolyzed with an XGA-specific hydrolase. These results confirm that the XGD1 protein is a XGA xylosyltransferase. The protein was shown by expression of a fluorescent fusion protein in N. benthamiana to be localized in the Golgi vesicles as expected for a glycosyltransferase involved in pectin biosynthesis.