A Blueprint for Cellulose Synthesis in Higher Plants

Cellulose is the world's most abundant biopolymer and is an important source for industrial applications, such as textiles, paper and biofuel. Cellulose is also essential for directed, or anisotropic, cell growth and therefore also for plant morphogenesis. The cellulose polymer is synthesized at the plasma membrane by hexameric cellulose synthase (CESA) complexes. We have shown that many genes that are transcriptionally coordinated, or co-expressed, with the CESA genes are also involved in the production of cellulose, or cellulose-related polymers. For example, the CSI1/POM2 gene product appears to contribute to the guidance of the CESA complexes along cortical microtubules, and aids the insertion of the CESAs into the plasma membrane. While these co-expression relationships have proven useful for the identification of new players for cellulose synthesis, it is likely that conserved co-expression relationships across species would indicate a stronger link between a certain gene function and a biological process. We have constructed genome-level co-expression networks for seven plant species and compared network vicinities to identify genes that co-occur in these networks. In addition, we have discovered that the cellulose-related co-expressed gene vicinity has been duplicated multiple times in Arabidopsis, and that the new co-expressed modules perform functions related to tip growth. These types of analyses may also be readily extended to other cellular processes within a certain species, but also across species and Kingdoms.