Figure 36 Model of plant cell wall (Source:
Somerville et al. 2004)PLANT PRODUCTIVITY AND BIOFUEL PRODUCTION
Broad implementation of biomass as an important energy source in the United States and in the
world could potentially be facilitated by the genetic modification of plants for enhanced
productivity, improving stress tolerance and minimizing exogenous nutrient inputs. Knowledge
of the molecular and physiological mechanisms by which plants acquire drought, salt, or cold
tolerance are likely to be important in permitting rational improvement of biomass crops. A
related long-term objective is the incorporation of biological nitrogen fixation capability into
non-legumes to improve the efficiency of plant production. The requirement for nitrogen
fertilizer represents up to 25% of the cost of biomass production. Worldwide, approximately 160
million tons of NH 3 are produced annually by an energetically expensive fossil fuel-dependent
process that could be displaced by biological nitrogen fixation.
CELL WALL BIOSYNTHESIS AND BIOFUEL PRODUCTION
Plant biomass consists largely of cell walls composed of polysaccharides and lignin, as shown in
Figure 36. Relatively little is known about how the polysaccharides are synthesized or deposited
during cell wall synthesis; most of the enzymes that catalyze synthesis of the major
polysaccharides have not been characterized, and due to technical difficulties, essentially nothing
is known about how wall polysaccharide composition is regulated. Recent advances in genomics
and analytical chemistry have created new opportunities to make rapid progress in understanding
how walls are synthesized and assembled. Additionally, new molecular imaging technologies
may allow elucidation of the structure of
assembled cell walls. The identification of the
genes and corresponding enzymes involved in
cell wall polysaccharide synthesis and assembly,
and knowledge of the design principles, will
create novel opportunities to genetically improve
the composition of cell walls for various uses
ranging from fiber applications to biofuels
production. It seems likely that by altering the
genetic control of cell wall composition, plants
can be developed with significantly increased
biomass accumulation. Additionally, cell wall
composition can be tailored to meet various end
uses related to different options in biomass
processing for biofuels.
MICROBES AND SOLAR BIOFUELS
Microorganisms represent a vast repository of biochemical diversity that remains largely
unknown and untapped. Thirty to 50% of the coding capacity of microorganisms represents
genes of unknown function, and less than 1% of all microorganisms can be cultivated in the
laboratory. This biochemical diversity holds solutions for improving processes (e.g., cellulose or
sugar transformations, lignin degradation, etc.) for biofuels production as well as the production