Finding ways to secure our energy future

Plants build a biological fortress around one of their most important jewels: sugars. They fortify a wall with a substance called lignin, whose name in Latin means wood.
When scientists want to turn plants into biofuel, their first step is to delignify the plant, or, as Ronald Reagan might say, to “tear down that wall” to free up the sugars. The process is expensive and reduces the energy efficiency of using plants for biofuel.

Brookhaven National Laboratory biologist Chang-Jun Liu has been working for over four years to figure out how to get plants to produce less lignin, i.e., to produce walls that would be weaker, making it easier to get at those precious sugars.

Liu, Kewei Zhang, Mohammed-Wadud Bhuiya and Yuchen Miao, along with a team from the University of Wisconsin, needed to figure out how to reduce the amount of lignin in the walls without destroying a plant’s ability to grow. Lignin, after all, is necessary to help a plant maintain its structure and climb toward the light.

Liu and the team of scientists looked for ways to send a signal to the plant that the work of putting lignin together was done before the walls of the lignin fortress became too strong. The process of building a complex polymer like lignin involves putting many steps together. What Liu created was a premature “good to go” signal so that the plant produced walls with less lignin.

The scientists tested over a thousand different classes of enzymes that might interfere with the process of forming lignin. By 2009, they had found that an enzyme that naturally occurs in plants but has a different function might do the trick. If they mutated (or genetically altered) two key amino acids in the enzyme, it would change the lignin in such a way that would prevent the molecules from coupling to form a tight bond.
While the amino acid changes worked outside the plant in lab experiments, they didn’t work when used in a live plant. Using BNL’s National Synchrotron Light Source to determine the enzyme’s crystal structure, they discovered more amino acid mutations that worked.

The new enzyme reduced lignin by 24 percent, leading to a 21 percent increase in the release of cell wall sugars.

At the same time, though, the reduced lignin didn’t affect the plant’s ability to develop and grow, a key consideration in the development of biofuel.

“You can’t see any difference in the plant,” Liu explained.

Liu remained aware of the delicate balance between weakening the lignin to gain easier access to the cellulose sugars in the cell wall and the need to leave enough for the plant to survive.

Lignin is involved in water transportation, allowing the leaves at the top of the plant to receive water delivered from the soil. Lignin also provides a physical barrier to prevent a plant from becoming too susceptible to damage from changes to the environment or from insect attacks.

“Within a certain range, the plant can still survive well,” Liu offered. “We think our method compared with others is an advantage.”

Liu has inserted his enzyme into poplar trees to reduce lignin. He is seeking collaborators to test whether the lignin reduction will help in promoting the conversion of wood into bioethanol with laboratory scale fermentation. He is discussing this with scientists at SUNY Syracuse.

Liu recognizes the benefit of contributing to improving the nature of biofuel production.

“Biofuel is one of the solutions to reduce our dependence on fossil fuels,” he explained. “Currently, our ability to convert to biofuel is low.”

Natives of China, Liu and his wife Yang Chen, who works as a special education aid at Rocky Point Middle School, moved to Oklahoma in 1999. That’s where their children, who now attend the middle school and elementary school in Rocky Point, were born.

After a brief stopover in California, Liu joined BNL in 2005. He enjoys hiking and walking in the state park with his family.

As far as his research, Liu hopes it will benefit his children’s generation.

“We have to find a way to secure our energy future,” he explained. “We have to find alternative sources of energy to meet our needs.”