Lack of α-Xylosidase Activity in Arabidopsis Alters Xyloglucan Composition and Results in Growth Defects    

Abstract

Xyloglucan is the main hemicellulose in the primary cell walls of most seed plants and is thought to play a role in regulating the separation of cellulose microfibrils during growth. Xylose side chains block the degradation of the backbone, and a-xylosidase activity is necessary to remove them. Two Arabidopsis (Arabidopsis thaliana) mutant lines with insertions in the a-xylosidase gene AtXYL1 were characterized in this work. Both lines showed a reduction to undetectable levels of a-xylosidase activity against xyloglucan oligosaccharides. This reduction resulted in the accumulation of XXXG and XXLG in the liquid growth medium of Atxyl1 seedlings. The presence of XXLG suggests that it is a poor substrate for xyloglucan b-galactosidase. In addition, the polymeric xyloglucan of Atxyl1 lines was found to be enriched in XXLG subunits, with a concomitant decrease in XXFG and XLFG. This change can be explained by extensive exoglycosidase activity at the nonreducing ends of xyloglucan chains. These enzymes could thus have a larger role than previously thought in the metabolism of xyloglucan. Finally, Atxyl1 lines showed a reduced ability to control the anisotropic growth pattern of different organs, pointing to the importance of xyloglucan in this process. The promoter of AtXYL1 was shown to direct expression to many different organs and cell types undergoing cell wall modifications, including trichomes, vasculature, stomata, and elongating anther filaments.

Group III-AXTHGenes of Arabidopsis Encode Predominant Xyloglucan Endohydrolases That Are Dispensable for Normal Growth

“…However, these results do not support XEHs as major actors in controlling cell wall extension. The XEHs encoded by AtXTH31 and AtXTH32 may instead be the key enzymes in a xyloglucan-recycling pathway composed of recently discovered Arabidopsis a-L-fucosidases, b-galactosidases, a-xylosidases, b-glucosidases, and their homologs, which are similarly up-regulated in cells undergoing wall extension and/or remodeling (Iglesias et al, 2006;Sampedro et al, 2010Sampedro et al, , 2012Günl et al, 2011). In light of our current work and these recent analyses, continued scrutiny of the role of polysaccharide hydrolases in the context of cell wall morphogenesis is clearly warranted.…”

Xyloglucan Metabolism Differentially Impacts the Cell Wall Characteristics of the Endosperm and Embryo during Arabidopsis Seed Germination

“…Yet size reduction in siliques was correlated with increased width in both xyl1 and xxt1 xxt2 and to a lesser extent in bgal10 and axy8, strongly suggesting a more predominant role of XyG metabolism in directional growth in these organs than hypocotyls (Supplemental Fig. S3; Sampedro et al, 2010;.…”

Xyloglucanendo-Transglycosylase-Mediated Xyloglucan Rearrangements in Developing Wood of Hybrid Aspen

“…Indeed, the size and composition of xyloglucan residing in cell walls can vary substantially as a result of transglycosylation, endohydrolysis, and trimming by wall-residing XETs, a-xylosidases and b-glucosidases, and endoglucanases, respectively (Kaida et al, 2010;Sampedro et al, 2010). However, there have been no demonstrations that different plant tissues synthesize and secrete xyloglucan chains of differing length.…”