Abstract
The xyloglucan endotransglucosylase/hydrolases (XTHs) are a family of enzymes that catalyze xyloglucan endotransglucosylase and/or xyloglucan endohydrolase activities and, thereby, play a principal role in the construction and restructuring of xyloglucan cross-links in the cellulose/xyloglucan framework. In angiosperm, XTHs constitute large multigene families, which probably reflect the diverse roles of XTHs for the diversity of cell types. Although the bryophyte has fewer cell types than angiosperm, the Physcomitrella patens XTH (PpXTH) gene family consists of 32 members, which is comparable in size with those previously defined in two fully sequenced angiosperm genomes. Extensive comparative analyses of XTH families in P. patens and angiosperms suggest that numerous bryophyte-specific XTH genes have evolved to meet the morphological and physiological needs of the bryophytes. These surprising findings raise interesting questions about the biological importance of XTHs in basal land plants.
