Functional diversity of xyloglucan-related proteins and its implications in the cell wall dynamics in plants

The plant cell wall is a dynamic apparatus responsible for both morphogenes is and responsiveness to environmental conditions. In the cell wall of most seed plants, cellulose microfibrils are cross-linked by xyloglucans to for m a cellulose/xyloglucan framework, which functions as the mechanical under pinning of the cell wall. Endoxyloglucan transferases are a class of enzyme s that play a central role in construction and modification of the plant ce ll wall. These enzymes are encoded by a large multi-gene family termed xylo glucan-related proteins (XRPs). More than 24 members of the XRP family have so far been identified in Arabidopsis thaliana. Each member of this family functions as either a hydrolase or a transferase acting an xyloglucans. Th e primary structures of proteins and gene-expression profiles have strongly suggested their potentially divergent roles in plant morphogenesis: differ ent members of this family are expressed in different types of tissues at d istinct developmental stages and respond differentially to individual hormo nes as well as environmental stimuli. These facts imply that each member of this gene family is individually committed to a specific process that proc eeds in a specific tissue at a specific stage of development. Probably the generation and maintenance of the cell walls in a whole organ, and thus in the whole plant, is achieved by the ensemble of individual members of the X RP family.