Pathways and genes involved in cellulose biosynthesis.

Abstract

For many years, progress in the field of cellulose biosynthesis was hampered by inability to characterize enzymes or genes involved in the process. However, two breakthroughs led the study of this process into a new era. The first was the discovery in 1987 of cyclic diguanylic acid as a unique activator of a bacterial cellulose synthase, a finding that opened the way for enzyme purification and characterization (1). The second breakthrough came in 1990 with the first cloning of genes involved in the process (2,3). In this review, we have attempted to provide an overview of this complex process for those new to the field. In addition, we have made efforts to review critically genes and proteins, and motifs within those proteins, that could be potential future targets for genetic engineering to improve or alter cellulose production in plants and bacteria. We have also tried to point out some of the many remaining unanswered questions in cellulose synthesis and discuss them from different angles, hoping that this review will initiate constructive debates and stimulate new directions for research. We will focus on the following issues: (i) a discussion of various models for the pathway of cellulose synthesis in bacteria and plants; (ii) bacterial operons involved in cellulose synthesis; (iii) celA genes isolated recently from cotton and rice; (iv) an analysis of motifs for binding of the substrate UDP-glucose (UDP-Glc); and (v) mechanisms involved in the crystallization and deposition of cellulose microfibrils in the plant cell wall. Since determination of cellulose structure and mode of biosynthesis are not new subjects of study, a large number of reviews on the subject has been published (1,4–15). For those new to the field, we highly encourage the reader to read at least some of these other reviews to comprehend the complexity and controversy that has been characteristic of this field since each review has a different emphasis and viewpoint.KeywordsCotton FiberCellulose MicrofibrilCellulose SynthesisCellulose BiosynthesisDirect PolymerizationThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.