Overproduction of fungal endo-β-1,4-glucanase leads to characteristic lignocellulose modification for considerably enhanced biomass enzymatic saccharification and bioethanol production in transgenic rice straw

Abstract

Genetic modification of plant cell walls has been considered to reduce lignocellulose recalcitrance for enhanced biomass enzymatic saccharification and biofuel production in bioenergy crops. Although endo-β-1,4-glucanase (EG II) secreted by fungi has been broadly applied for enzymatic hydrolysis of cellulose, it remains to explore its role in cellulose modification when the EG II gene is overexpressed in plant. In this study, we selected transgenic rice plants that overproduced Trichoderma reesei EG II enzyme specifically deposited into plant cell walls, and then examined much higher enzymatic activities by fourfold to fivefold in transgenic young seedlings than those of wild type in vitro. Notably, despite slightly altered cell wall compositions and polymer interlinkages relative to the wild type, the transgenic mature rice straw exhibited significantly reduced cellulose DP and CrI values and hemicellulosic Xyl/Ara ratio, leading to much increased biomass porosity. These should play integrated impact for enhanced biomass enzymatic saccharification and bioethanol production even under mild alkali pretreatment. Therefore, the results suggested that the EG II deposition should have enzymatic activity specific for minor-modification of cellulose microfibrils in transgenic rice plants. It has also provided a potential strategy for mild cell wall modification and optimal biomass process in rice and other bioenergy crops.