British researchers unlock sugar secret

By Kris Bevill | August 27, 2010
Posted Sept. 15, 2010

A long-term research project being funded by Britain's Biotechnology and Biological Sciences Research Council achieved a significant breakthrough recently when researchers successfully modified plant genes to more easily access the sugars locked inside lignocellulose. The finding could result in more cost-effective cellulosic ethanol conversion from plant matter such as corn stover and miscanthus, as well as woody biomass.

The research team's discovery centered around the modification of enzymes that control xylan, one of the main components of lignocellulose. Approximately one-third of a plant's sugars that could be used for ethanol production are locked away inside the xylan, according to lead researcher and University of Cambridge professor Paul Dupree. Until the discovery, it has been problematic for researchers to determine how to access those sugars. "We don't understand how that sugar is locked away and why it's difficult to release sugar that can be fermented," Dupree said. "What we have discovered is one of the ways that the plant makes it difficult for us and how to overcome that. The consequences are that when this is deployed it should be cheaper and use less energy to release the sugars from maize stover, wheat straw, wood, and that makes [ethanol production] more economically viable."

After identifying the two enzymes that appeared to control the xylan portion of lignocellulose in plants, the University of Cambridge research team, which is part of the BBSRC's sustainable bioenergy center, experimented with growing Arabidopsis plants that lacked those two enzymes. "What we didn't want to do was end up with floppy plants that can't grow properly, so it was important to find a way of making xylan easier to break down without having any major effects," Dupree said. Surprisingly, what they discovered was that the altered plants functioned just as well as the traditional plants. "If you put them side-by-side, you wouldn't be able to see any difference at all," he said. "We can detect some difference, but it's not a large difference. So one of the important discoveries is that it is possible to change the structure to make it easier to extract the sugars and you don't necessarily end up with severely weakened plants. It makes it worthwhile trying to improve the plant material."

Work will immediately begin on using this knowledge to access sugars located in willow trees and, eventually, energy crops such as miscanthus and corn stover. Dupree's team will focus on willow research because it can be readily grown in the U.K. and harvested in three-year cycles, he said.

The results of this scientific breakthrough could be applied in several ways, according to Dupree. The first is breeding of new plant varieties that lack the xylan-controlling enzymes. Creating genetically modified crops is also an option. Finally, it could also lead to an alteration of the enzymes used in cellulosic ethanol production. "So now we know how the plant has locked the sugars away a little bit more, perhaps in the processing process where we extract the sugars we can use that knowledge to modify our processing," he said. "That could also be faster than modifying the plants themselves."

Dupree said the next stage of research will include close collaboration with industrial partners to determine how quickly research results can be translated into real applications for transportation fuels.