Xyloglucan endotransglucosylase/hydrolases of Arabidopsis: Expression and function of a gene family

The plant cell wall is a complex structure composed in part of cellulose microfibrils interconnected by a network of hemicellulose. The most abundant hemicellulose of dicotyledonous plants is xyloglucan. Xyloglucan endotransglucosylase/hydrolases (XTHs) cleave xyloglucan polymers and religate the newly generated reducing ends to other xyloglucan polymers (Rose et al., 2002). Analysis of the Arabidopsis database reveals an extensive gene family that encodes thirty-three XTH proteins. These proteins are highly similar and share a conserved motif that is predicted to be necessary for their activity, as well as N-linked glycosylation sites and putative signal sequences for translation at ER membranes. Although the biochemical activity of this enzyme is well defined, the physiological consequences of XTH activity in vivo remain undetermined. XTH biochemical activity, however, predicts a role in modification of the cell wall. An attempt was started to elucidate the physiological functions of the 33 XTHs of Arabidopsis. From this work, 47 mutations were identified in 28 XTH genes. Mutations in XTH15 were chosen for detailed study. Theses mutants exhibit a shorter phenotype than wild type when grown at higher temperatures. This difference may be due to the misshapen cell morphology observed in the xth15 mutants through microscopy. XTH gene expression was examine through the use of reporter-gene fusions with the beta-glucuronidase (GUS) gene as well as by compiling evidence of expression from various on-line databases, such as the Genevestigator website. Overall, divergent XTH expression patterns are observed from the earliest stages of seed germination through flowering. XTH::GUS patterns and data from other expression sources show some overlap which may result in novel combinations of XTH activities in distinct cells or organs