DOE JGI Director Eddy Rubin highlights the genomics of plant-based biofuels in the jour...(he deconstruction of cell wall polymers ...)

"With the data that we are generating from plant genomes we can home in on relevant agronomic traits such as rapid growth, drought resistance, and pest tolerance, as well as those that define the basic building blocks of the plants cell wallcellulose, hemicellulose and lignin. Biofuels researchers are able to take this information and design strategies to optimize the plants themselves as biofuels feedstocksaltering, for example, branching habit, stem thickness, and cell wall chemistry resulting in plants that are less rigid and more easily broken down."

For microbial biomass breakdown, Rubin says that many candidates have already been identified. These include Clostridia species for their ability to degrade cellulose, and fungi that express genes associated with the decomposition of the most recalcitrant features of the plant cell wall, lignin, the phenolic "glue" that imbues the plant with structural integrity and pest resistance. The white rot fungus Phanerochaete chrysosporium produces unique extracellular oxidative enzymes that effectively degrade lignin by gaining access through the protective matrix surrounding the cellulose microfibrils of plant cell walls.

Another fungus, the yeast Pichia stipitis, ferments the five-carbon "wood sugar" xylose abundant in hardwoods and agricultural harvest residue. Rubin says that Pichia's recently sequenced genome has revealed insights into the metabolic pathways responsible for this process, guiding efforts to optimize this capability in commercial production strains. Pathway engineering promises to produce a wider variety of organisms able to ferment the full repertoire of sugars derived from cellulose and hemicellulose and tolerate higher ethanol concentrations to opti
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