Genetically Modified Poplar

What began 20 years ago as an innovation to improve paper industry processes and dairy forage digestibility may now open the door to a much more energy- and cost-efficient way to convert biomass into fuel. A collaboration between researchers at the University of British Columbia, the University of Wisconsin-Madison, and Michigan State University, the breakthrough could herald a greener future for biofuels.
“We’re designing trees to be processed with less energy and fewer chemicals,” says Shawn Mansfield, a professor of Wood Science at the University of British Columbia. “It is truly a unique achievement to design trees for deconstruction while maintaining their growth potential and strength.”
The research, which appears in the current issue of Science Magazine, focuses on enhancing poplar trees so they can break down easier and thus improving their viability as a biofuel. The long-term efforts and teamwork involved to find this solution can be described as a rare, top-down approach to engineering plants for digestibility, said Curtis Wilkerson, Michigan State University plant biologist and the lead author.
“By designing poplars for deconstruction, we can improve the degradability of a very useful biomass product,” said Wilkerson. “Poplars are dense, easy to store and they flourish on marginal lands not suitable for food crops, making them a non-competing and sustainable source of biofuel.”
In the new study, the researchers found a gene from an herb DangGui, or Chinese angelica, and successfully put it into poplar trees, a fast-growing crop widely planted throughout the United States and Canada.
The resulting poplar trees showed no difference in growth habit under greenhouse conditions, but the lignin from those plants showed improved degradation properties, the researchers said.

Lignin and Biofuels

They determined that the gene modified the poplars’ natural lignin to make it easier to break down without adversely affecting the trees’ strength.
The code alters the chemistry of some of the bonds that hold together lignin, the organic polymer glue that makes trees tough and rigid and protects the energy-rich cellulose within cells. The genetically engineered poplars are every bit as strong as normal poplars while they are living, but when processed the lignin “unzips” where the altered bonds occur in the polymer chain.
Removing naturally occurring lignin for the production of bioethanol and paper products requires caustic chemicals and high heat, about 170 C for several hours. Zip-lignin falls apart in a mild alkaline solution at just 100 C.
Using the new method plant life can be broken down using fewer chemicals and less energy. This will mean fewer environmental pollutants are created.
To produce the enhanced poplars, Wilkerson identified and isolated a gene capable of making monomers – molecular glue of sorts – with bonds that are easier to break apart. Next, Mansfield  successfully put that gene into poplars. The team then determined that the plants not only created the monomers but also incorporated them into the lignin polymer. This introduced weak links into the lignin backbone and transformed the poplars’ natural lignin into a more easily degradable version.

Introducing really cleavable linkages into the lignin polymer backbone. SOURCE:  Shawn Mansfield, UBC, and Matt Wisniewski, Madison, WI
Introducing really cleavable linkages into the lignin polymer backbone.
SOURCE: Shawn Mansfield, UBC, and Matt Wisniewski, Madison, WI

The research also is noteworthy for being the direct result of a collaboration funded by the GLBRC, funded by the US Department of Energy and created to make transformational breakthroughs in new cellulosic biofuels technology. Realizing the collaborative project called for a wide array of expertise, from finding the gene and introducing it into the plants, to proving, via newly designed analyses, that the plant was utilizing the new monomers in making its lignin.
“One of the largest impediments for the pulp and paper industry as well as the emerging biofuel industry is a polymer found in wood known as lignin,” says Mansfield.
Lignin makes up a substantial portion of the cell wall of most plants and is a processing impediment for pulp, paper, and biofuel. Currently the lignin must be removed, a process that requires significant chemicals and energy and causes undesirable waste.
The genetic modification strategy employed in this study could also be used on other plants like grasses to be used as a new kind of fuel to replace petroleum.
Genetic modification can be a contentious issue, but there are ways to ensure that the genes do not spread to the forest. These techniques include growing crops away from native stands so cross-pollination isn’t possible; introducing genes to make both the male and female trees or plants sterile; and harvesting trees before they reach reproductive maturity.
In the future, genetically modified trees could be planted like an agricultural crop, not in our native forests. Poplar is a potential energy crop for the biofuel industry because the tree grows quickly and on marginal farmland. Lignin makes up 20 to 25 per cent of the tree and is is an important part of plant cell walls.
Mansfield said he’s confident these trees are viable for commercial use, especially since the team chose to modify poplar trees that can be grown virtually anywhere in Canada.
“It is truly a unique achievement to design trees for deconstruction while maintaining their growth potential and strength,” the researchers noted in the study published in the journal Science.