SGR Promoter-Controlled EXG1 Gene Enhances Saccharification in Rice

Cellulose, the most abundant biomass, is valuable to the production of biofuels. However, the plant cell walls, which contain the cellulose, are physically strong and biochemically stable. Previous studies have tried to solve this problem including the utilization of rice gene EXG1, which encodes exo-glucanase. The gene was overexpressed resulting in enhanced saccharification ability of the rice straws. However, there were also various developmental defects present due to the modified cell wall.

For the study, the same EXG1 gene was expressed in transgenic plants but was under the control of the STAY GREEN (SGR), a senescence-inducible promoter. The transgenic plants showed enhanced saccharification efficiencies after senescence. Meanwhile, no significant difference was observed on saccharification efficiencies before senescence. Neither morphological abnormality nor sterility were present in the EXG1-expressing transgenic plants.

These results indicate that expression of cell wall degrading enzymes such as cellulase through a senescence-inducible promoter is capable of enhancing the saccharification ability of biomass without affecting plant growth.