Cellulose biosynthesis in plants: from genes to rosettes.

Modern techniques of gene cloning have identified the CesA genes as encoding the probable catalytic subunits of the plant CelS, the cellulose synthase enzyme complex visualized in the plasma membrane as rosettes. At least 10 CesA isoforms exist in Arabidopsis and have been shown by mutant analyses to play distinct role/s in the cellulose synthesis process. Functional specialization within this family includes differences in gene expression, regulation and, possibly, catalytic function. Current data points towards some CesA isoforms potentially being responsible for initiation or elongation of the recently identified sterol beta-glucoside primer within different cell types, e.g. those undergoing either primary or secondary wall cellulose synthesis. Different CesA isoforms may also play distinct roles within the rosette, and there is some circumstantial evidence that CesA genes may encode the catalytic subunit of the mixed linkage glucan synthase or callose synthase. Various other proteins such as the Korrigan endocellulase, sucrose synthase, cytoskeletal components, Rac13, redox proteins and a lipid transfer protein have been implicated to be involved in synthesizing cellulose but, apart from CesAs, only Korrigan has been definitively linked with cellulose synthesis. These proteins should prove valuable in identifying additional CelS components.