Rice gene helps unlock poplar sugars for biofuels

Man standing next to a group of young poplar trees with his arm extended to just above his head
GLBRC scientist Steven Karlen demonstrates the height that poplar saplings reached in their first year of growth at the Wisconsin Energy Institute at UW–Madison. GLBRC scientists have engineered a strain of the fast growing tree with a rice gene to make it easier to break apart biomass for plant-based fuels and chemicals.
Chelsea Mamott/Wisconsin Energy Institute

Scientists with UW–Madison’s bioenergy research hub have modified poplar trees with a rice gene, making them easier to break down into more sustainable replacements for fossil fuels and petrochemicals.

Trees and other woody plants are made up of polymeric sugars, cellulose and hemicellulose, which are surrounded by a tough substance known as lignin, which provides structure to plants. Together, these molecules are an abundant and renewable source of sugars and aromatic compounds that can be turned into fuels, lubricants, plastics, and even pharmaceuticals. 

The challenge is breaking apart lignin’s strong and complex chemical bonds. 

In order to tap into the sweet potential, Great Lakes Bioenergy Research Center collaborators showed in 2014 that they could genetically engineer trees with a weaker chemical linkage in the lignin backbone, making them more easily degradable. 

“We’re at a crossroads. We need to develop innovative tools to improve the processing of materials, fuels, and food. Moreover, we need to be able to produce more resources on smaller spaces and in a faster time frame with less energy inputs. These trees are key.”

Shawn Mansfield, GLBRC co-investigator

A decade later, in a paper published in the journal Biotechnology for Biofuels and Bioproducts, GLBRC scientists have described a new genetic modification that is about 10 times more effective than the previously patented technology. By strategically inserting weak linkages into the lignin, acids and bases are able to more easily degrade the lignin’s complex chemical bonds.

The original strategy, trademarked as Zip-Lignin, introduced a gene from a Chinese medicinal herb into poplar, a fast-growing hardwood tree targeted as a bioenergy crop.

The leaves from young poplars glow yellow from the sun.
A stand of poplars at Michigan State University's Kellogg Biological Research Station. Gabe De La Rosa/Michigan State University

However, research collaborator Laura Bartley, a plant biology associate professor at Washington State University, found that a similar gene in rice had a greater effect on the molecular composition of lignin. 

Before it’s possible to process the lignin, it first has to undergo pretreatment to open the cell wall of the plant and expose its carbohydrates to enzymes that can free the simple sugars, a process Mansfield compares to making coffee: you have to roast and grind the beans before you can brew a cup to enjoy the caffeine. 

The new findings suggest that the modified lignin would yield the same amount of sugar with less energy and harsh chemicals, or even more sugar using traditional pretreatment methods. 

A headshot of Shawn Mansfield Mansfield

Mansfield, a professor of botany at the University of British Columbia, said this advancement could improve the economics of biorefineries as well as pulp and paper mills. 

“We’re at a crossroads,” Mansfield said. “We need to develop innovative tools to improve the processing of materials, fuels, and food. Moreover, we need to be able to produce more resources on smaller spaces and in a faster time frame with less energy inputs. These trees are key.”

The genetically modified poplars also incorporate multiple high-value chemicals that adhere to the lignin polymer and can be more easily recovered for industrial uses, including in bioplastics, cosmetics, and drug delivery components.

Mansfield noted that as the world’s population grows and modernizes, there is an increasing need for sustainable sources of fuel, fiber, and feed, including plant-derived toiletries and feminine hygiene products. These genetically engineered poplars are well suited to meet these demands.

Press Contacts:

Shawn Mansfield, shawn.mansfield@ubc.ca

John Ralph, jralph@wisc.edu

Sustainable Bioenergy Cropping Systems