SacEXP32 sugarcane expansin gene expression increases cell size and improves biomass digestibility

Cellulose is the major renewable feedstock used in a variety of industrial processes. However, its native state, organizing itself in microfibrils and interacting with other components of the cell wall complex, forms a highly recalcitrant structure. Expansin proteins may facilitate the enzymatic saccharification stage by affecting non-covalent bonds between the wall polymers. In the current study, the expression profile of five selected Expansin genes from sugarcane, an important crop in the supply of biomass lignocellulose for the ethanol industry, was analyzed in leaves, roots, and young culms. The SacEXP32 and SacEXP39 genes, potentially associated with the cell wall architecture modification in sugarcane culm, were selected for functional characterization studies in Nicotiana benthamiana using the agroinfiltration assay. Heterologous expression of SacEXP32 and SacEXP39 revealed that N. benthamiana cellulose synthase gene was positively regulated at the transcript level in transformed tissue. However, only SacEXP32 expression increased cell area and enzymatic saccharification efficiency. SacEXP32 overexpression may have influenced the network of all cell wall polymers, indicating that this gene is a potential target for biotechnological approaches to improve plant biomass industrial processing.