Recent progress in the field of cellulose synthesis

A putative gene for a beta-glucosyltransferase, celA, was isolated from cotton in 1996. Recently, a homologous gene RSW1 was identified from studies with a cell wall mutant of Arabidopsis. These two independent studies strongly suggest that celA is involved in cellulose synthesis in plants. In addition to the celA multigene family, two other related multigene families of putative beta-glycosyltransferases have been identified by the Arabidopsis genome projects. The celA-like superfamily of proteins all share conserved motifs that may be involved in substrate binding and/or catalysis. We discuss proposed reaction mechanisms by which plants make wall polysaccharides including cellulose. While recent advances in cellulose synthesis in vitro have unraveled some aspects involved in the processes, cellulose synthesis in vivo involves additional processes such as translocation of glucan products across the plasma membrane and the deposition of cellulose microfibrils in the cell wall. We discuss generally accepted models in which cellulose synthesizing complexes move in the plasma membrane during cellulose synthesis and deposition, and also describe an alternative model in which beta-transglucosylase activity of a hypothetical endo-1,4-beta-D-glucanase is involved in cellulose synthesis in plants.