Chris Somerville

Research/Lab website:   Chris Somerville Web Page

The research program in my lab is largely focused on trying to understand how plant cell wall polysaccharides are synthesized and how the structure of the polysaccharides relates to the functions of the cell wall. The enzymes that synthesize the polysaccharide components of plant cell walls are largely uncharacterized. The principal component of the wall, cellulose, is synthesized by the enzyme cellulose synthase, which is encoded by a family of ten CESA genes in Arabidopsis (http://cellwall.Stanford.edu). We are investigating the function of a family of related genes of unknown function that show sequence similarity to cellulose synthase. We have provisionally called these genes CSLs (Cellulose Synthase Like) (Richmond and Somerville, 2000). Our approach to assigning function to the CSL genes is to make mutations in the genes and to test for corresponding changes in cell wall composition that would indicate a possible enzymatic function. To date we have identified mutations in 29 of the CSL and CESA genes. The genes for which mutations have been identified are indicated by black boxes. We are currently analyzing the mutants by a variety of analytical methods such as FTIR spectroscopy of intact cell walls and measurements of the sugar composition of the main polysaccharides of the cell wall.

A related project concerns the analysis of mutants that exhibit altered sensitivity to chemicals that are thought to inhibit cellulose synthesis. Dale Heim and colleagues at Eli Lilly had previously isolated mutants of Arabidopsis, called ixr1 and ixr2, that are resistant to the herbicide isoxaben. We cloned the ixr1 locus and found that it encodes a CESA gene. The ixr1-1 and ixr1-2 alleles cause missense mutations in the last exon of the CESA gene. Thus, it seems likely that isoxaben interacts directly with cellulose synthase and may be a useful compound for future mechanistic studies of enzyme action. We are currently using the compound to examine the mechanisms by which plants sense and respond to changes in cell wall integrity. We have observed that following treatment of plants with isoxaben, large numbers of genes are rapidly activated. We have obtained insertion mutations in a number of the genes that are activated by isoxaben and are currently studying their role in cell wall biology.