Genetic Repressor Enhances Ethanol Yield of Engineered Switchgrass

The journal Biotechnology for Biofuels reported a 2.6-fold increase in cellulosic ethanol yield with a genetically engineered switchgrass (Panicum virgatum) that produces high levels of a genetic repressor.

Switchgrass has been recognized as a potential lignocellulosic material for biofuel production. Switchgrass, however, is hampered by the so-called recalcitrance problem as a result of the physical and chemical barriers within the biomass, such as lignin and phenolic fermentation inhibitors, that block access to fermentable sugars. Before the sugars can be fermented into biofuels, expensive pretreatment is required to deconstruct the biomass and expose its surfaces for enzymatic breakdown.

To address the problem of recalcitrance in switchgrass, a team of researchers from different US institutions employed a genetic engineering approach specifically by overexpressing the transcription factor referred to as PvMYB4, which represses the phenylpropanoid/lignin biosynthesis pathway genes. Elevated levels of PvMYB4 in genetically modified switchgrass plant significantly reduced the production of lignin and phenolic metabolites that are known fermentation inhibitors, while maintaining the availability of fermentable sugars, as shown by detailed biomass characterization. The strategy was also shown to increase the efficiency of biomass breakdown by up to 300 percent without pretreatment as well as the ethanol yield after 7 days of fermentation by about 2.6-fold compared to control material.

According to the team that published the study, the significant improvement in ethanol yield, proportional to the dramatic reduction of recalcitrance, makes the genetically engineered switchgrass an excellent model for understanding the chemical basis of recalcitrance, and for the development of economically viable lignocellulosic feedstocks for biofuel production.