Enhancing Poplar Traits for Energy Applications. Gaining a better understanding of genes and regulatory mechanisms that control growth, carbon allocation, and other relevant traits in the poplar tree (Populus trichocarpa) may lead to its use as a major biomass feedstock for conversion to bioethanol. An international team led by the DOE Joint Genome Institute recently completed sequencing the poplar genome, making it the first tree (and fourth plant, after the mustard weed Arabidopsis thaliana, rice, and the alga Chlamydomonas) to have its complete genome sequenced (Tuskan et al., in press). These data now offer the molecular access needed to define, quantify, and understand—at a mechanistic level—basic biological processes that impact important traits. Poplar was chosen for sequencing because of its relatively compact genome (500 million bases), only 2% that of pine. Moreover, many species are available worldwide, and their rapid growth allows meaningful measures of important traits within a few years. Extensive genetic maps already available include initial identification of markers associated with such traits.Early comparative sequence analyses of poplar and Arabidopsis genomes are providing insights into genome structure and gene-family evolution; biosynthetic processes such as cell-wall formation, disease resistance, and adaptation to stress; and secondary metabolic pathways. Comparisons of gene-family sizes show substantial expansion of poplar genes involved in carbon to cellulose and lignin biosynthesis. Moving from a descriptive to predictive understanding of poplar growth, development, and complex function will require integration of sequence information with functional data. These data will be generated by such new tools and approaches as gene and proteome expression studies, metabolic profiling, high-throughput phenotyping and compositional analysis, and modeling and simulation. Ultimately, this information will lead to the engineering of faster-growing trees that produce more readily convertible biomass (see below, Fig A. Vision for the Future). The International Populus Genome Consortium has produced a science plan to guide postsequencing activities (The Populus Genome Science Plan 2004–2009: From Draft Sequence to a Catalogue of All Genes Through the Advancement of Genomics Tools, web.ornl.gov/sci/ipgc/).Other areas to be addressed for poplar and other potential bioenergy crops include sustainability for harvesting biomass, harvesting technologies to remove biomass at low costs, and infrastructure technologies that allow biomass to be transported from harvest locations to conversion facilities.
Credit or Source: Biological and Environmental Research Information System, Oak Ridge National Laboratory. Sponsored by the U.S. Department of Energy Biological and Environmental Research Program.
U.S. DOE. 2006. Breaking the Biological Barriers to Cellulosic Ethanol: A Joint Research Agenda, DOE/SC/EE-0095, U.S. Department of Energy Office of Science and Office of Energy Efficiency and Renewable Energy. (p. 62) (website)