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

Cellulose synthesis in plants requires β-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-β-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.