Downregulation of Cinnamyl Alcohol Dehydrogenase (CAD) Leads to Improved Saccharification Efficiency in Switchgrass
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The bioconversion of carbohydrates in the herbaceous bioenergy crop, switchgrass (Panicum virgatum L.), is limited by the associated lignins in the biomass. The cinnamyl alcohol dehydrogenase (CAD) gene encodes a key enzyme which catalyzes the last step of lignin monomer biosynthesis. Transgenic switchgrass plants were produced with a CAD RNAi gene construct under the control of the maize ubiquitin promoter. The transgenic lines showed reduced CAD expression levels, reduced enzyme activities, reduced lignin content, and altered lignin composition. The modification of lignin biosynthesis resulted in improved sugar release and forage digestibility. Significant increases of saccharification efficiency were obtained in most of the transgenic lines with or without acid pretreatment. A negative correlation between lignin content and sugar release was found among these transgenic switchgrass lines. The transgenic materials have the potential to allow for improved efficiency of cellulosic ethanol production.
KeywordsCinnamyl alcohol dehydrogenase Lignin modification Panicum virgatum Saccharification Switchgrass Transgenic plant
We thank Ko Shimamoto for providing the pANDA vector, Human David for assistance with GC-MS and LC-MS analysis, Stacy Allen and Tui Ray for assistance with real-time RT-PCR analysis, and Dennis Walker for assistance with forage digestibility analysis. The work was supported by the US Department of Agriculture and US Department of Energy Biomass Initiative (project no. 2009-10003-05140), the BioEnergy Science Center and the Samuel Roberts Noble Foundation. The BioEnergy Science Center is supported by the Office of Biological and Environmental Research in the DOE Office of Science.
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