Researchers boost switchgrass potential with corn gene

By Holly Jessen | November 22, 2011

Searching for a way to get around lignin and produce advanced biofuels in a cost-efficient way, researchers introduced a maize gene into switchgrass. The result was a 250 percent increase in the amount of starch and an easier extraction of polysaccharides and conversion to fermentable sugars.

The research on Corngrass1, a variant of a maize gene, was conducted at the U.S. DOE’s Joint BioEnergy Institute (JBEI), a DOE Bioenergy Research Center led by the Lawrence Berkeley National Laboratory. The genetic modification works by keeping the switchgrass in the juvenile phase of development, which prevents flowering and seed production. “We show that Cg1 switchgrass biomass is easier for enzymes to break down and also releases more glucose during saccharification,” said Blake Simmons, a chemical engineer who heads JBEI’s Deconstruction Division and was one of the principal investigators for this research. “Cg1 switchgrass contains decreased amounts of lignin and increased levels of glucose and other sugars compared with wild switchgrass, which enhances the plant’s potential as a feedstock for advanced biofuels.”

The first Cg1 gene was discovered about 80 years ago, said George Chuck, a lead author of the study. That gene was cloned in 2007 and introduced into switchgrass, as well as other plants. “The natural function of Cg1 is to hold pants in the juvenile phase of development for a short time to induce more branching,” he said. “Our Cg1 variant is special because it is always turned on, which means the plants always think they are juveniles.”

Juvenile switchgrass plants have less lignin than adult plants. The plants also don’t produce seed, which adds up to more starch availability. Something researchers didn’t expect to happen was no flowering even after two years of growth. “The lack of flowering limits the risk of the genetically modified switchgrass from spreading genes into the wild population,” said Chuck, also a plant molecular geneticist who holds joint appointments at the Plant Gene Expression Center with ARS and the University of California (UC) Berkeley.

This research is a significant step in the direction of making switchgrass more digestible for advanced biofuel production. Still, there are more questions to be answered, such as the need for pretreatment for fermentation. “The alteration of the switchgrass does allow us to use less energy in our pre-treatments to achieve high sugar yields as compared to the energy required to convert the wild type plants,” Simmons said. “The results of this research set the stage for an expanded suite of pretreatment and saccharification approaches at JBEI and elsewhere that will be used to generate hydrolysates for characterization and fuel production.”

The research was published in the Proceedings of the National Academy of Sciences in a paper titled “Overexpression of the maize Corngrass1 microRNA prevents flowering, improves digestibility, and increases starch content of switchgrass.” It was supported in part by the DOE’s Office of Science and by the USDA-ARS. The paper’s authors include Simmons, Chuck, Christian Tobias, Lan Sun, Florian Kraemer, Chenlin Li, Dean Dibble, Rohit Arora, Jennifer Bragg, John Vogel, Seema Singh, Markus Pauly and Sarah Hake.