Cell Wall Biosynthesis

Abstract

Abstract Plant cell walls encase the plant cells and provide many structural and functional roles. Cell walls are complex structures consisting mainly of polysaccharides (cellulose, hemicellulose and pectin), glycoproteins and phenolic compounds (lignin). Most plant cell wall polymers are synthesised from ‘activated’ precursors by the action of transferases. Cellulose is synthesised at the plasma membrane (PM) by a large complex moving in the plane of PM and extruding cellulose chains into the wall. The hemicelluloses are synthesised in the endomembrane system by resident glycosyl transferase enzymes and transported to the wall. These individual components are then cross‐linked and assembled into the complex matrix structure that comprises functional cell walls. Woody cell walls also contain lignin. Lignin is synthesised in the wall by oxidative coupling of individual monomeric subunits. Key Concepts All plant cells are encased in a multilayered cell wall. Plant cell walls are an important renewable resource. Plant cell walls are composed of polysaccharides (cellulose, hemicellulose and pectin), cell wall proteins and phenolic compounds. Most of the polysaccharides are synthesised from activated precursors, NDP sugars and incorporated into the growing polymer catalysed by the action of glycosyl transferases (GTs). Cellulose is synthesised by the cellulose synthase complex (CSC) moving in the plane of plasma membrane, extruding cellulose chains into the cell wall. Hemi‐celluloses and pectin are synthesised and modified in the endomembrane system before being deposited into the apoplast for assembly into the cell wall. Lignin monomers are synthesised in the cytoplasm and transported to the wall. Laccases have an essential role in lignin formation by catalysing the oxidative coupling of the lignin monomers in the apoplast. Cell wall composition varies greatly between cell types and can change as the cell differentiates and with the developmental stages of cells and the plant. The cell wall has an important function in regulating how plant cells achieve their final size and shape and consequently have an essential role in regulating plant growth.