Sitosterol-β-glucoside as Primer for Cellulose Synthesis in Plants

Abstract

Cellulose synthesis in plants requires beta-1,4-glucan chain initiation, elongation, and termination. The process of chain elongation is likely to be distinct from the process of chain initiation. We demonstrate that a CesA glucosyltransferase initiates glucan polymerization by using sitosterol-beta-glucoside (SG) as primer. Cotton fiber membranes synthesize sitosterol-cellodextrins (SCDs) from SG and uridine 5'-diphosphate-glucose (UDP-Glc) under conditions that also favor cellulose synthesis. The cellulase encoded by the Korrigan (Kor) gene, required for cellulose synthesis in plants, may function to cleave SG from the growing polymer chain.

Expression of a Mutant Form of Cellulose Synthase AtCesA7 Causes Dominant Negative Effect on Cellulose Biosynthesis

“…The monosaccharide donor substrate used by CesAs, UDP-Glc, has been postulated to be provided by membrane-associated form(s) of Suc synthase (Amor et al, 1995). Recent in vitro studies suggest that the initiation of ␤-1,4-glucan synthesis starts with the addition of Glc units to a primer, sitosterol lipid, to form lipid-linked oligosaccharides called sitosterol cellodextrin (Peng et al, 2002). Cellodextrins are then thought to be cleaved from the sitosterol primer probably by a KOR cellulase (Nicol et al, 1998) and further elongated by addition of more Glc molecules to form a long chain of ␤-1,4-glucan (Peng et al, 2002).…”

“…Recent in vitro studies suggest that the initiation of ␤-1,4-glucan synthesis starts with the addition of Glc units to a primer, sitosterol lipid, to form lipid-linked oligosaccharides called sitosterol cellodextrin (Peng et al, 2002). Cellodextrins are then thought to be cleaved from the sitosterol primer probably by a KOR cellulase (Nicol et al, 1998) and further elongated by addition of more Glc molecules to form a long chain of ␤-1,4-glucan (Peng et al, 2002). It is not known whether each CesA protein is involved in both initiation and elongation of the sugar chains, or different CesA proteins play different roles in this process (Read and Bacic, 2002).…”

Quantitative Trait Loci and Comparative Genomics of Cereal Cell Wall Composition

“…Biochemical approaches to identification of the enzymes and genes involved have been hindered by the lability of the enzymes and our ignorance of their biosynthetic mechanisms. Although substantial progress has recently been made on the identification and function of cellulose synthases and the corresponding genes (called CESA) and on several nonprocessive glycosyl transferases such as xylosyl, galactosyl, and fucosyl transferases, little is known about the genes and enzymes involved in synthesis of the backbones of the hemicellulosic polymers (Arioli et al, 1998;Edwards et al, 1999;Perrin et al, 1999;Fagard et al, 2000;Taylor et al, 2000;Faik et al, 2002;Peng et al, 2002;Vanzin et al, 2002).…”

Integrative Theory of the Mode of Action of Quinclorac: Literature Review1

“…The role of CESas is to transfer glucose residues from a nucleotide to the glycan chain that is being formed (Paredez et al, 2006). Sterol-glycosides (sterols connected to a chain of two or three glucose residues) are the originators or the initial acceptors of the glycan formation (Peng et al, 2002). The sterol group is then removed from the glycan by endoglucanase.…”