One of the most efficient solutions to fighting climate change could be growing in your backyard. Trees are essential for removing carbon dioxide from the air while simultaneously releasing oxygen. Estimates suggest a mature tree absorbs over 48 pounds of carbon dioxide in the atmosphere per year—but there is still room for improvement. Now, in a study published today in the journal Science, an interdisciplinary team of chemists, engineers, and environmental scientists are optimizing the way trees can further help to create a sustainable future.
To do that, they are delving into trees’ genetic makeup. “I don’t think the general public fully understands or appreciates the impact trees have on our society and in reducing carbon emission. Understanding the genetics of this critical resource is important, especially for producing fibers that’s important in our buying economy,” says Daniel Sulis, a postdoctoral scholar at North Carolina State University and lead study author.
Sulis and his colleagues have made the first successful attempt to use gene editing to streamline the process of wood fiber production. The authors modified the genetics of poplar trees to reduce the amount of lignin—an organic component that acts as the backbone to give trees its rigid and woody structure. By reducing the amount of this hard structural material that trees produce, paper production takes less time and, in turn, causes less pollution.
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“We’ve been studying lignin for decades, but the complexity of those polymers inside of wood makes it really hard to modify in ways that are compatible with processing applications for productions,” says Jack Wang, an assistant professor at North Carolina State University’s College of Natural Resources and one of the authors of the study.
To create renewable paper tissue and other products, the lignin in wood must be cut and dissolved with hazardous chemicals. This is an energy-intensive process, and it releases carbon dioxide when the lignin is burned, which can contribute atmospheric emissions in the atmosphere.
In the current study, the team idea used CRISPR—molecular scissors that cut up and modify specific DNA segments—to reduce lignin levels and increase carbohydrates. That carbohydrate, as cellulose, is desirable because it’s what gets pulped into paper products.
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The team used machine learning predictive models to narrow 70,000 possible gene editing strategies and potential targets to less than 350. Follow-up experiments to see which would produce wood compatible with fiber production led the the authors to choose seven strategies, almost all of which targeted more than one gene.
Their goal: Create trees with 35 percent less lignin than those found in nature. They also wanted their carbohydrate-to-lignin ratio to be 200 percent higher than unedited trees. With CRISPR gene editing, they created 174 different lines of poplar trees, which they grew in a greenhouse for six months.
An analysis of the tree’s wooden composition after six months revealed less lignin in the trees. Some had half the amount as a normal poplar tree. There was also a 228 percent increase in the carbohydrate-to-lignin content.
“The capability to precisely control lignin content enables new processes to use wood fibers in paper and advanced engineered wood,” says Liangbing Hu, the director for the Center for Materials Innovation at Maryland Energy Innovation Institute who has published research on new approaches for engineering cellulose in wood but wasn’t involved in the current study. “For example, pulp production using edited wood with reduced lignin can provide substantial benefits to climate change mitigation.”
Poplar trees edited to have less lignin could reduce the carbon footprint of fiber production by over 20 percent, the team’s analysis found. “This turned out to be a technology that is not only beneficial for the sustainability efficiency of our economy, but at the same time, creates solutions for more environmentally friendly production of this material,” Wang adds.
The demand for wood fiber is growing as society looks for more green-friendly products, such as renewable tissues, paper towels, and textiles. Gene-edited trees may also yield more product: A separate analysis in the study estimated that trees with less lignin could produce 40 percent more sustainable fibers.
The next step is to apply this gene editing strategy to other hardwood trees commonly used in paper production such as spruce and pine. Since the mechanism for how wood produces lignin is fairly the same across multiple tree species, Wang says it is possible to try this technique out on other tree types. Another direction the team is pursuing is planting these trees in huge fields, and seeing how the edited trees interact with the environment, measuring how they behave and sustain themselves.
Because it takes a long time for these trees to mature for use in fiber production, it will be around 2040 when society starts seeing more of them, Wang says. What’s more, as concerns over releasing gene-edited mosquitoes show, local support would be crucial. For successful and responsible applications of this technology, he says, “we have to ensure that whatever we do fully aligns with not only governmental regulations but also public acceptance and industry interests.”
