The synthesis of xyloglucan, an abundant plant cell wall polysaccharide, requires CSLC function

Abstract

Xyloglucan (XyG) is an abundant component of the primary cell walls of most plants. While the structure of XyG has been well studied, much remains to be learned about its biosynthesis. Here we employed reverse genetics to investigate the role ofArabidopsiscellulose synthase like-C (CSLC) proteins in XyG biosynthesis. We found that single mutants containing a T-DNA in each of the fiveArabidopsis CSLCgenes had normal levels of XyG. However, higher-ordercslcmutants had significantly reduced XyG levels, and a mutant with disruptions in all fiveCSLCgenes had no detectable XyG. The higher-order mutants grew with mild tissue-specific phenotypes. Despite the apparent lack of XyG, thecslcquintuple mutant did not display significant alteration of gene expression at the whole-genome level, excluding transcriptional compensation. The quintuple mutant could be complemented by each of the fiveCSLCgenes, supporting the conclusion that each of them encodes a XyG glucan synthase. Phylogenetic analyses indicated that theCSLCgenes are widespread in the plant kingdom and evolved from an ancient family. These results establish the role of theCSLCgenes in XyG biosynthesis, and the mutants described here provide valuable tools with which to study both the molecular details of XyG biosynthesis and the role of XyG in plant cell wall structure and function.