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Published on March 21, 2008; 10.1104/pp.107.115576

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Received December 26, 2007
Accepted March 15, 2008

UDP-xylose stimulated glucuronyltransferase activity in wheat (Triticum aestivum L.) microsomal membranes: Characterization and role in glucurono(arabino)xylan biosynthesis

Wei Zeng , Mohor Chatterjee , and Ahmed Faik *

Department of Environmental and Plant Biology, Molecular and Cellular Biology Program, Ohio University, Athens, OH 45701, USA

* Corresponding author; email: faik{at}ohio.edu.

Microsomal membranes from etiolated wheat (Triticum aestivum L.) seedlings cooperatively incorporated xylose, arabinose, and glucuronic acid residues from their corresponding uridine 5'-diphosphosugars into an ethanol-insoluble glucurono(arabino)xylan(GAX)-like product. A glucuronyltransferase activity that is enhanced by the presence of uridine diphosphate xylose was also identified in these microsomes. Wheat glucuronyltransferase activity was optimal at pH7, required manganese ions, and several lines of evidence suggest its involvement in GAX-like biosynthesis. The GAX characteristics of the [14C]product were confirmed by digestion with a purified endo-xylanase from Aspergillus awamori (endo-xylanase III) and by total acid hydrolysis resulting in a xylose:arabinose:glucuronic acid molar ratio of ~105:34:1, respectively. Endo-xylanase III released only three types of oligosaccharides in addition to free xylose. No [14C]radiolabel was released as xylobiose, xylotriose, or xylotetraose indicating the absence of long stretches of unbranched xylose residues in the nascent GAX-like product. High pH Anion Exchange Chromatography analysis of the resulting oligosaccharides along with known arabinoxylan oligosaccharide standards suggests that portion of the nascent GAX-like has a relatively regular structure. The other portion of the [14C]GAX-like polymer was resistant to proteinase K, endo-polygalacturonase, and endo-xylanase III (GH11 family), but was degraded by Driselase supporting the hypothesis that the xylan backbone in this portion of the product is most likely highly substituted. Size exclusion chromatography indicated that the nascent GAX-like polymer had an apparent molecular mass of ~10-15kD, however, mature GAXs from wheat cell walls had larger apparent molecular masses (larger than 66kD).






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