Exploiting evolutionary diversity of cellulose synthase catalytic subunits to generate novel cellulose microfibril structure in Arabidopsis

Cellulose is pivotal in regulating plant cell size and shape, and represents an abundant renewable resource for producing materials and chemicals. In seed plants, cellulose is synthesized at the plasma membrane by a hexameric protein complex synthesizing 18 glucose chains that bond together to form a microfibril; however, significant variation exists in the structure and physical properties of cellulose synthesized by other species and between different cell types. In this study, we surveyed the ability of 15 different catalytic subunits of the cellulose synthase complex (CESA proteins) derived from four species of charophycean green algae, a lycophyte, a bryophyte, and a fern to synthesize cellulose in the Arabidopsis secondary cell walls. Several CESA proteins can function in Arabidopsis in conjunction with endogenous CESA proteins in a pattern not easily predictable based on phylogenetics, demonstrating that heterologous expression is a valuable functional analysis tool. Additionally, two moss CESA proteins synthesized cellulose without Arabidopsis CESAs. The cellulose produced by the moss CESA proteins exhibited a much higher proportion of surface-exposed glucose residues but was sufficient to support normal plant growth. This study demonstrates that heterologous expression of CESA proteins generates cellulose with novel structures that offer a more suitable feedstock for biotechnological applications.