A major assumption in much plant-focused bioenergy research is that key plant cell wall traits can be genetically manipulated to reduce recalcitrance and increase biofuel yields per unit of biomass. A number of greenhouse experiments have shown promise, but few field studies have been completed to assess this assumption. Researchers at the BioEnergy Science Center (BESC) are the first to report a field study evaluating the biofuel potential of genetically engineered switchgrass (Panicum virgatum L.). BESC researchers previously had used RNAi (inhibitory RNA) to down-regulate caffeic acid O-methyltransferase (COMT), a key enzyme in the synthesis of lignin precursors. Switchgrass plants engineered in this way and grown in the greenhouse had less lignin and a shift in the quality of lignin to a more hydrolysable form. These plants showed less recalcitrance and a greater percentage of cell wall sugars being converted to ethanol than control plants. However, greenhouse results do not always replicate in the field, so researchers were anxious to learn if COMT-engineered switchgrass would show reduced recalcitrance and increased ethanol production when grown in the field.
The 2-year field trial in large part recapitulated the greenhouse results. Namely, the transgenic switchgrass plants had a reduction in the quantity of lignin and a shift in the quality of lignin. A greater percentage of the cell wall sugars were released with pretreatment, and ethanol yield increased by as much as 28% in the transgenic lines relative to controls. These results were with senescent tissues, whereas the greenhouse studies had only looked at green tissues. Importantly for agronomic applications, the transgenic plants were not more susceptible to rust (Puccinia emaculata) or other plant pests. This important 2-year field study affirms genetic engineering of the plant cell wall as a viable strategy to improve plant biomass for the production of high-energy biofuels.
Reference: Baxter, H. L.; M. Mazarei; N. Labbe; L. M. Kline; Q. Cheng; M. T. Windham; D. G. J. Mann; C. Fu; A. Ziebell; R. W. Sykes; M. Rodriguez, Jr.; M. F. Davis; J. R. Mielenz; R. A. Dixon; Z. W. Wang; and C. N. Stewart, Jr. 2014. “Two-Year Field Analysis of Reduced Recalcitrance Transgenic Switchgrass,” Plant Biotechnology Journal 1–11. DOI:10.1111/pbi.12195. (Reference link)
Contact: Kent Peters, SC-23.2, (301) 903-5549
SC-33.2 Biological Systems Science Division, BER
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