Wednesday, November 7, 2007 - 1:30 PM
256-2
Lignin Modification Overcomes Recalcitrance for Production of Liquid Biofuels.
Lignocellulosic bioenergy crops such as switchgrass (Panicum virgatum), Miscanthus x giganteus, poplar species and alfalfa (Medicago sativa) hold promise as sustainable sources of biomass for ethanol production. Unlike corn, in which the fermentable sugar originates from starch, biomass from the above plants is first processed (saccharification) to convert hemicellulosic and cellulosic cell wall polysaccharides to their constituent pentose and hexose sugars by sequential acid and enzymatic hydrolysis; the released sugars are then fermented to ethanol. Recalcitrance to saccharification is recognized as the major limitation to efficient conversion of lignocellulose to ethanol. We have shown, by exploiting a series of transgenic alfalfa lines independently down-regulated in six enzymes of lignin biosynthesis, that recalcitrance to saccharification of stem tissues to both acid pre-treatment and cellulase digestion is inversely proportional to their lignin content. Lignin composition did not affect enzymatic saccharification of acid-pretreated tissues. Transgenic plants with reduced lignin content could yield more than twice as much fermentable sugar from cell wall polysaccharides as did wild-type plants, a finding with significant implications for the cost-effectiveness of bioethanol. Reducing lignin content may allow for elimination of the costly acid-pretreatment step, thereby facilitating bioprocess consolidation. Additional targets for genetic manipulation to improve cell wall deconstruction, and the impacts of lignin modification on plant growth, will be discussed.
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