Expression of Acidothermus cellulolyticus thermostable cellulases in tobacco and rice plants

The production of cellulases in plants is an economical method for the conversion of lignocellulosic biomass into fuels. Herein we report the expressions of two thermostable Acidothermus cellulolyticus cellulases, endo-1,4-beta-D-glucanase (E1) and exoglucanase (Gux1), in tobacco and rice. To evaluate the expression of these recombinant cellulases, we expressed the full-length E1, the catalytic domains of E1 (E1cd) and Gux1 (Gux1cd), as well as an E1-Gux1cd fusion enzyme in various subcellular compartments. In the case of tobacco, transgenic plants that expressed apoplast-localized E1 showed the highest level of activity, about three times higher than those that expressed the cytosolic E1. In the case of rice, the level of cellulase-specific activity in the transgenic plants ranged from 11 to 20 nmol 4-methylumbelliferone min(-1) mg(-1) total soluble protein. The recombinant cellulases exhibited good thermostability below 70 degrees C. Furthermore, transgenic rice leaves that were stored at room temperature for a month lost about 20% of the initial cellulase activity. Taken together, the results suggested that heterologous expression of thermostable cellulases in plants may be a viable option for biomass conversion.