Cellulose Biosynthesis in Plants: from Genes to Rosettes

Abstract

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.

Global expression analysis of CESA and CSL genes in Arabidopsis

“…A CESA10::GUS promoter fusion indicates that CESA10 is expressed at the base of rosette leaves in Arabidopsis, which correlates with the very weak expression of the gene on the gene chips (Doblin et al 2002). A mutation in CSLD3 caused a defect in root hair cell wall formation (Favery et al 2001).…”

The Genetics and Transcriptional Profiles of the Cellulose Synthase-Like HvCslF Gene Family in Barley

“…Amino acid sequence identity values range from 40% to 63% overall (Table I), although higher identity values are observed in some segments of the proteins (data not shown). The putative catalytic site residues D, D, D, QxxRW (Doblin et al, 2002) are evident (Fig. 2) but no obvious signal peptides or other common peptide motifs are present.…”

“…These are large integral membrane proteins, containing up to 1,000 amino acid residues and up to eight transmembrane helices, and were traditionally believed to catalyze the synthesis of the backbones of wall homopolysaccharides such as cellulose or of wall heteropolysaccharides such as heteroxylans, xyloglucans, or glucomannans (Doblin et al, 2002). The type I polysaccharide synthases are encoded by members of a large multigene family known as the cellulose synthase (CesA) superfamily (Richmond and Somerville, 2000).…”

Structure, organization, and functions of cellulose synthase complexes in higher plants

“…In fact, orthologs of AtCesA1, AtCesA3, and AtCesA6 appear to be required for the synthesis of cellulose deposited in the primary cell walls (Fagard et al, 2000;Scheible et al, 2001;Burn et al, 2002;Doblin et al, 2002). In contrast, orthologs of AtCesA4, AtCesA7, and AtCesA8 seem to be essential for cellulose synthesis in the secondary cell walls (Turner and Somerville, 1997;Taylor et al, 1999Taylor et al, , 2000Taylor et al, , 2003Zhong et al, 2003).…”

“…Several models have been proposed to explain interactions among CESA isoforms, allowing proper formation of CelS (Scheible et al, 2001;Doblin et al, 2002;Joshi, 2003a). These models are based on the hypothesis that one elementary fibril is composed of 36 glucose chains, which are synthesized by 36 CESA isoforms arranged in a planar configuration in the plasma membrane (Delmer, 1999;Kimura et al, 1999;Scheible et al, 2001).…”