Miron Abramson

Genetic Modifications of Plant Cell Walls to Increase Biomass and Bioethanol Production

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.

The Modification of Cell Wall Properties by Expression of Recombinant Resilin in Transgenic Plants

Plant tissue is composed of many different types of cells. Plant cells required to withstand mechanical pressure, such as vessel elements and fibers, have a secondary cell wall consisting of polysaccharides and lignin, which strengthen the cell wall structure and stabilize the cell shape. Previous attempts to alter the properties of the cell wall have mainly focused on reducing the amount of lignin or altering its structure in order to ease its extraction from raw woody materials for the pulp and paper and biorefinery industries. In this work, we propose the in vivo modification of the cell wall structure and mechanical properties by the introduction of resilin, an elastic protein that is able to crosslink with lignin monomers during cell wall synthesis. The effects of resilin were studied in transgenic eucalyptus plants. The protein was detected within the cell wall and its expression led to an increase in the elastic modulus of transgenic stems. In addition, transgenic stems displayed a higher yield point and toughness, indicating that they were able to absorb more energy before breaking.