Abstract
The hemicellulose xyloglucan consists of a backbone of a β‐1,4 glucan substituted with xylosyl moieties and many other, diverse side chains that are important for its proper function. Many, but not all glycosyltransferases involved in the biosynthesis of xyloglucan have been identified. Here, we report the identification of an hitherto elusive xyloglucan:arabinopyranosyltransferase. This glycosyltransferase was isolated from the moss Physcomitrella patens, where it acts as a xyloglucan “D”‐side chain transferase (XDT). Heterologous expression of PpXDT in the Arabidopsis thaliana double mutant mur3.1 xlt2, where xyloglucan consists of a xylosylated glucan without further glycosyl substituents, results in the production of the arabinopyranose‐containing “D” side chain as characterized by oligosaccharide mass profiling, glycosidic linkage analysis, and NMR analysis. In addition, expression of a related Physcomitrella glycosyltransferase ortholog of PpXLT2 leads to the production of the galactose‐containing “L” side chain. The presence of the “D” and “L” xyloglucan side chains in the Arabidopsis double mutant Atmur3.1 xlt2 expressing PpXDT and PpXLT2, respectively, rescues the dwarfed phenotype of untransformed Atmur3.1 xlt2 mutants to nearly wild‐type height. Expression of PpXDT and PpXLT2 in the Atmur3.1 xlt2 mutant also enhanced root growth.
Highlights
The plant cell wall is a complex extracellular matrix composed of polysaccharides such as cellulose, hemicellulose, and various pectic polysaccharides, glycoproteins and the polyphenol lignin
The amino acid sequence of the Arabidopsis XyG-related GT47 family member AtMUR3 was used as a bait to identify related GT candidates of Physcomitrella present in the Joint Genome Institute database Phytozome
The xylosyl residue of XyG is often substituted at the O-2 position with a variety of glycosyl residues including galactosyl, galacturonosyl, xylopyranosyl, arabinofuranosyl or arabinopyranosyl moieties [1]
Summary
The plant cell wall is a complex extracellular matrix composed of polysaccharides such as cellulose, hemicellulose, and various pectic polysaccharides, glycoproteins and the polyphenol lignin. The major hemicellulose xyloglucan (XyG) is found in all land plants and is especially abundant in the primary cell wall of dicots [1]. XyG in the primary cell wall attaches to cellulose microfibrils non-covalently via H-bonds and its metabolism in the wall is thought to play a role in cell elongation [2, 3, 4]. It was thought that a particular XyG structure is plant species specific, but recently tissue specific structures within a plant species have emerged [9, 10, 11]. XyG has been found in higher plants, and in non-vascular plants such as liverworts and mosses [12]
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