Berkeley researcher significantly increases starch in switchgrass

By Erin Voegele | October 20, 2011

A researcher at the University of California, Berkeley is working to genetically modify biomass feedstocks in a way that could dramatically increase starch production. The project, led by Research Geneticist George Chuck, involves the introduction of the gene corngrass1 into the genetic makeup of switchgrass.

According to Chuck, this project began six years ago when he was working on a maize variant known as corngrass. “Its genotype is that the plants are stuck in a juvenile phase of development, which is great from a biomass perspective because they keep making all these branches, so you get more biomass,” he said. “And the tissue is less lignified because juvenile biomass don’t produce a whole lot of lignin.”

Chuck and his team cloned the gene, and set out to see if they could use it to help improve the properties of a biofuels crop like switchgrass. The gene was inserted into switchgrass, and the resulting plants became stuck in the juvenile phase. “One aspect of being juvenile is that the plants never sexually mature, so they never produce flowers, which is good and bad,” Chuck said. “It’s good in that the plants will never spread their DNA to other plants—you won’t get seeds or pollen—the drawback is that it will be hard to plant because you can’t plant seed.”

Since the genetically modified plants don’t flower, they build up significant carbon reserves. One example of carbon reserves is starch level, Chuck said. “We measured the starch levels and it was about 2.5-fold more starch in our plants compared with normal plants,” he said. As a result, enzymes could be used to convert the starch into sugar in the same way that they are used to convert corn starch into fermentable sugars. According to Chuck, preliminary results show that the resulting sugar levels would be comparable to those achieved through the expensive pretreatment of standard switchgrass for cellulosic conversion. “The benefit here is that you skip the entire pretreatment process, so you save on the cost of heating up the biomass, adding all these caustic chemicals, like acids and bases, so you don’t need to do any of that stuff and you can get the same amount of sugar out,” he explained.

 The research is still in a preliminary stage. According to Chuck, a small field trial of approximately 24 plants has been completed to date. So far, Chuck has expressed the genes in all areas of the plants, including the roots, which affects the plant’s growth. “Now, I’m trying to be a little more precise and specific about when and where I turn the gene on,” he said. There is also ongoing research to try the same genetic technique with other biomass crops such as sorghum.

A report outlining Chucks’ research was published in the Oct. 10 issue of the Proceedings of the National Academy of Sciences.