Secondary cell wall biosynthesis

Secondarywalls are synthesizedin specializedcells, suchas tracheary elements andfibers, and their remarkable strength andrigidityprovide strongmechanical support tothe cells andthe plant body. The main components of secondary walls are cellulose, xylan, glucomannan and lignin. Biochemical, molecular and genetic studies have led to the discovery of most of the genes involved in the biosynthesis of secondary wall components. Cellulose is synthesized by cellulose synthase complexes in the plasma membrane and the recent success of in vitro synthesis of cellulose microfibrils by a single recombinant cellulose synthase isoform reconstituted into proteoliposomes opens new doors to further investigate the structure and functions of cellulose synthase complexes. Most genes involved in the glycosyl backbone synthesis, glycosyl substitutions and acetylation of xylan and glucomannan have been genetically characterized and the biochemical properties of some of their encoded enzymes have been investigated. The genes and their encoded enzymes participating in monolignol biosynthesis andmodification have been extensively studied both genetically and biochemically. A full understanding of how secondary wall components are synthesized will ultimately enable us to produce plants with custom-designed secondary wall composition tailored to diverse applications.