Sunday, May 4, 2008 - 4:30 PM
1-05

Development of Low-lignin Biomass Feedstock for Improved Biofuel Production

Fang Chen, Rui Zhou, Jin Nakashima, Gail Shadle, Lisa Jackson, and Richard A. Dixon. Plant Biology Division, Samuel Roberts Noble Foundation, 2510 Sam Noble Parkway, Ardmore, OK 73401

The accessibility of plant cell wall polysaccharides to chemical, enzymatic and microbial degradation is limited by many factors, including the presence of lignin. Lignin is a polymer of hydroxylated and methoxylated phenylpropane units linked via oxidative coupling. It accumulates in secondary cell walls during the development of vascular tissues and fibers, and imparts both mechanical strength and hydrophobicity. The composition and structure of lignified cell walls has a dramatic impact on the technological value of raw materials, and has been identified as a key factor limiting effective biomass to biofuel conversion in processes where the sugar components of polysaccharides are released prior to fermentation to ethanol. In addition to physically preventing access of microbial enzymes to cellulose, lignin may also exert a negative impact on bioethanol production through its partial degradation to inhibitors of the microbial fermentation system. A series of transgenic lines of alfalfa (Medicago sativa) were generated in which either one of the two potentially terminal enzymes of the monolignol pathway, cinnamoyl CoA reductase, coniferyl alcohol dehydrogenase and 4-(hydroxy)cinnamoyl CoA ligate, was down-regulated by expression of antisene genes.  Transgenic plants with reduced lignin content could yield more fermentable sugar from cell wall polysaccharides as did wild-type plants, a finding with significant implications for the cost-effectiveness of bioethanol. The relationship between lignin and saccharification of plant cell walls for bioethanol production will be discussed.  Additional targets for genetic manipulation to improve cell wall deconstruction, and the impacts of lignin modification on plant growth, will also be discussed.

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