Cell Wall Engineering by Heterologous Expression of Cell Wall-Degrading Enzymes for Better Conversion of Lignocellulosic Biomass into Biofuels

Abstract

Huge energy demand with increasing population is addressing renewable and sustainable energy sources. A solution to energy demand problem is to replace our current fossil fuel-based economy with alternative strategies that do not emit carbon dioxide. Plant biomass is one of the best candidates for this issue. Plants use solar power to convert carbon dioxide and water into sugars, which can be used in fermentation reactions to produce both energy and materials. However, the desired sugars are trapped in the highly recalcitrant cell wall as building blocks of cellulose chains. Moreover, the complexity of the plant cell wall structure hinders the hydrolysis of cellulose into fermentable sugar monomers. Although pretreatments are used to change the physical and chemical properties of the lignocellulosic biomass and improve hydrolysis rates, these pretreatments often use harsh and polluting chemicals and severely increase the cost of biofuel production. The goal of the review is to summarize recent researches, which describe generating plants with a modified cell wall and improve hydrolysis of cellulose without applying any or less pretreatment methods. Since pretreatment of lignocellulosic biomass is the most cost effective step in biofuel production, generating autodigestible plants could reduce the production cost of biofuels and bio-based biomaterials. One of the strategies to improve biomass conversion efficiency is the modification of the cell wall by heterologous expression of cell wall-modifying proteins. These cell wall-modifying proteins could alter the cell wall structure and reduce cell wall recalcitrance. The use of such transgenic technologies would consume less energy and chemicals when cellulose is more accessible for enzymatic hydrolysis.