Abstract
Switchgrass is a leading dedicated bioenergy feedstock because it is a native, high yielding, perennial prairie grass with broad cultivation range and low agronomic input requirements. Biomass conversion research has developed pilot scale processes for production of ethanol and other alcohols but they remain costly primarily due to the intrinsic recalcitrance of biomass. We show here that switchgrass genetic modification can produce normal plants that have reduced thermochemical and enzymatic recalcitrance. Downregulation of the switchgrass caffeic O-methyltransferase gene decreases lignin content modestly, reduces the syringyl to guaiacyl lignin monomer ratio and increases the ethanol yield by up to a third using conventional biomass fermentation processes. The downregulated lines have wild-type biomass yields but require reduced pretreatment severity and 300-400% lower cellulase dosages for equivalent product yields significantly lowering processing costs. Alternately, our modified transgenic switchgrass lines should yield significantly more fermentation chemicals per hectare under identical process conditions.