Abstract
Xyloglucans (XGs) are major components of dicot cell walls and function as cross-links between cellulose microfibrils. Xyloglucan endotransglucosylase/hydrolases (XTHs), which catalyze cleavage and reconnection of the XG cross-links, are considered to play important roles in construction and reorganization of cell walls in dicots.
XTHs are widely found in terrestrial plants. In Arabidopsis thaliana, Oryza sativa and the moss, Physcomitrella patens, XTHs are encoded by large gene families. This raises a question about roles of XTH in monocots and mosses. For, XG is a minor component in rice cell wall, and XGs in P. patens are, if any, distinct from that in dicots in terms of structural feature. This imply that rice and P. patens XTHs possess different roles than those of dicots.
To test the possibility, we analyzed their biological functions and enzymatic activities using recombinant proteins. Three rice OsXTHs exhibited transglucosylase activity and / or hydrolase activity on XG, suggesting that XG is the substrate for XTH in rice. We are now working on functions of the XTH in P. patens which lacks signal peptide and is not secreted into the cell wall.
