Genetic modifications of plant cell walls to increase biomass and bioethanol production

Abstract

To date, most ethanolic fuel is generated from first generation crop feedstocks by conversion of soluble sugars and starch to bioethanol. However, these crops exploit land resources required for production of food. On the other hand, utilization of second generation lignocellulosic biofuels derived from the inedible parts of plants remains problematic as high energy inputs and harsh conditions are required to break down the composite cell walls into fermentable sugars. This chapter reviews and discusses genetic engineering approaches for the generation of plants modified to increase cellulose synthesis, enhance plant growth rates, cell wall porosity and solubility, as well as improve cell wall sugar yields following enzymatic hydrolysis. Strategies focusing on increased accessibility of cellulose-degrading enzymes to their substrates have been developed. These approaches reduce cell wall crystallinity or alter the hemicellulose-lignin complexes. A novel approach to cell wall modification involving the introduction of noncrystalline, soluble polysaccharides into cell walls is also presented. The use of such approaches may promote and accelerate the future use of lignocellulosic feedstocks for the bioethanol industry.