Crop Biotech Update

Plant Genetic Engineering For Low Cost Cellulose-Ethanol Production

May 30, 2008
http://www.nature.com/nrg/journal/v9/n6/abs/nrg2336.html (full access to the paper may require paid subscription)
A recent review by Professor Mariam Sticklen of the Michigan State University’s Department of Crop and Soil Sciences ( in the United States) describes the potentials of plant genetic engineering for decreasing the production cost of cellulose-ethanol. Cellulosic biomass is said to be the bioethanol feedstock of the future, due to the following characteristics: (1) relatively abundant renewable resource (i.e. feedstock supply can keep up with “staggering” global ethanol demand), (2) non-food resource (no adverse effect on food security), and (3) ability to grow in non-agricultural/marginal lands with lower agricultural inputs. However, the barrier to realizing large-scale, commercial processing of cellulosic biomass to ethanol, is the cost of production. Cellulose-ethanol is estimated to be about two to three times the cost of grain-ethanol. The cellulose-ethanol production process usually involves: (1) pretreatment of the biomass to remove lignin and render the cellulose accessible to cellulose-degrading enzymes (“cellulases”), (2) enzymatic degradation/conversion of the cellulose into simple sugars by cellulases, and (3) fermentation of the simple sugars to ethanol. The high cost of cellulose-ethanol production has been attributed to the high cost of enzymes, and the high cost of pretreatment (energy-intensive processes, usually requiring extreme temperature/pressure conditions). The review paper describes some strategies by which plant genetic engineering can be harnessed to produce “tailored, third-generation cellulosic feedstocks” that can help reduce the costs of pretreatment and cellulase enzymes. Among the plant modification strategies are: (1) production/accumulation of cellulases in sub-cellular components in the plant, and (2) reduction of lignin content/structure in the plant. Details of these strategies, status of research, as well as challenges for the future are also described. The paper appears in a recent issue of the journal, Nature (URL above)..