Expression of Glycosyl Hydrolases in Lignocellulosic Feedstock: An Alternative for Affordable Cellulosic Ethanol Production

Ethanol produced from lignocellulosic feedstock is a promising alternative to fossil fuels and corn-sourced ethanol. However, it creates unique challenges in terms of requirements for breakdown to fermentable sugars, including the need for pretreatment and enzymatic hydrolysis of structural carbohydrates. Hydrolases from microorganisms are currently utilized for biomass hydrolysis in the production of lignocellulosic ethanol; however, expressing these hydrolases in lignocellulosic feedstock is a favorable alternative, due to the large availability of biomass and the potential for the feedstock to play a dual role as both biomass substrate and enzyme provider. This review summarizes recent achievements in hydrolytic enzyme expression in a variety of model plants and potential feedstocks, including strategies to improve enzyme yield and to prevent deleterious effects on plants hosts. We propose possible scenarios for utilizing enzyme-expressing transgenic feedstock and illustrate the potential benefits of using these crops for ethanol production. Furthermore, challenges are highlighted and potential solutions proposed to move the field forward to cost-comparable lignocellulosic ethanol.