Opportunities for Plant Biotechnology in Biomass Conversion

The three largest cost barriers to commercialization of the DOE Office of the Biomass Program-sponsored biochemical approach ('Sugar Platform') to biomass conversion are: the delivered cost of feedstock material to a processing facility; the thermochemical pretreatment process; and enzyme and process for saccharifying cellulose. The Biomass Program is focusing efforts on each of these, and iscurrently partnering with USDA/ARS, universities and equipment manufacturers to improve the logistics and economics associated with production, harvesting and storage of agricultural residues, such as corn stover and wheat straw. Over the last four years the Biomass Program has made a considerable investment in multi-year subcontracts with two large enzyme manufacturers to reduce the productioncost and improve the performance of cellulase enzymes for use in biomass conversion processes. Substantial progress has been made toward the goal of reducing cellulase cost, but more progress is necessary to reach the Biomass program's goal of $0.10/gal ethanol produced. These efforts have focused on technology that can impact industrial submerged culture fungal fermentation processes.Meanwhile, over the last 5-10 years, several academic and commercial labs have demonstrated the feasibility of producing individual cellulase enzymes (and other cell wall degrading enzymes) in a variety of plant species, tissues and organelles. This approach to producing cellulase enzymes has many advantages, including scalability over a wide range, low production costs, and minimal additionalcapital investment, among others. Moreover, this approach, if applied to the saccharification of both hemicellulose and cellulose, has the potential to eliminate the need for thermochemical pretreatment processes, which addresses one of the other barriers. However, issues of how to economically recover and/or utilize plant-expressed enzymes remain to be solved. The plant science community isalso learning how to manipulate the synthesis, assembly and degradation of plant cell walls. Manipulation of plant cell wall-related genes has already been shown to alter the chemical composition of cell walls in woody and herbaceous species. It is not known how these chemical changes might impact biomass processing. Plant cell wall engineering may also be able to alter wall architecture,thereby potentially rendering them easier to dismantle and further reducing processing costs. The development of technology enabling the degradation of the refractory lignin component of biomass into its monomeric units could facilitate development of economic biomass conversion processes while providing a more valuable by-product that could be used in the chemical industry.