Title
Enzymic characterization of two recombinant xyloglucan endotransglucosylase/hydrolase (XTH) proteins of **Arabidopsis** and their effect on root growth and cell wall extension
Author
Faculty/Department
Faculty of Sciences. Biology
Publication type
article
Publication
Oxford ,
Subject
Biology
Source (journal)
Journal of experimental botany. - Oxford
Volume/pages
60(2009) :13 , p. 3959-3972
ISSN
0022-0957
ISI
000269609800027
Carrier
E
Target language
English (eng)
Full text (Publishers DOI)
Affiliation
University of Antwerp
Abstract
Xyloglucan endotransglucosylase/hydrolases (XTHs) are enzymes involved in the modification of load-bearing cell wall components. They cleave xyloglucan chains and, often, re-form bonds to the non-reducing ends of available xyloglucan molecules in plant primary cell walls. The enzymic properties and effects on root growth of two Arabidopsis thaliana XTHs belonging to subgroup I/II, that are predominantly expressed in root hairs and in non-elongating zones of the root, were analysed here. AtXTH14 and AtXTH26 were recombinantly produced in Pichia and subsequently purified. Both proteins were found to exhibit xyloglucan endotransglucosylase (XET; EC 2.4.1.207 [EC] ) but not xyloglucan endohydrolase (XEH; EC 3.2.1.151 [EC] ) activity. Their endotransglucosylase activity was at least 70x greater on xyloglucan rather than on mixed-linkage â-glucan. Differences were found in pH- and temperature-dependence as well as in acceptorsubstrate preferences. Furthermore, the specific activity of XET was approximately equal for the two enzymes. Removal of N-linked sugar residues by Endo H treatment reduced XET activity to 60%. Constant-load extensiometry experiments revealed that the enzymes reduce the extension in a model system of heat-inactivated isolated cell walls. When given to growing roots, either of these XTH proteins reduced cell elongation in a concentration-dependent manner and caused abnormal root hair morphology. This is the first time that recombinant and purified XTHs added to growing roots have exhibited a clear effect on cell elongation. It is proposed that these specific XTH isoenzymes play a role in strengthening the side-walls of root-hairs and cell walls in the root differentiation zone after the completion of cell expansion.
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