CELLULOSE BIOSYNTHESIS: Exciting Times for A Difficult Field of Study.

The past few decades have witnessed exciting progress in studies on the biosynthesis of cellulose. In the bacterium Acetobacter xylinum, discovery of the activator of the cellulose synthase, cyclic diguanylic acid, opened the way for obtaining high rates of in vitro synthesis of cellulose. This, in turn, led to purification of the cellulose synthase and for the cloning of genes that encode the catalytic subunit and other proteins that bind the activator and regulate its synthesis and degradation, or that control secretion and crystallization of the microfibrils. In higher plants, a family of genes has been discovered that show interesting similarities and differences from the gene in bacteria that encodes the catalytic subunit of the synthase. Genetic evidence now supports the concept that members of this family encode the catalytic subunit in these organisms, with various members showing tissue-specific expression. Although the cellulose synthase has not yet been purified to homogeneity from plants, recent progress in this area suggests that this will soon be accomplished.