How gene editing could fight chestnut tree blight and avert extinction
Saving the American chestnut could restore a piece of history, resurrect a lost ecosystem and combat climate change. But critics say it would come at a cost.
The team gloves the fingerlike flowers with white bags and zip-ties them — an effort to control the flow of pollen. In a few months, genetically modified chestnuts will be ready for harvest.
“We open them up, and it’s like Christmas every time,” said LoPiccolo, a recent graduate of the State University of New York College of Environmental Science and Forestry (SUNY ESF).
These trees once ruled the canopies of much of Appalachia, with billions of mature American chestnut trees that towered in leafy forests from Maine to Mississippi. But around the beginning of the 20th century, an exotic fungus nearly drove the tree out of existence. Today, they still sprout in the wild but rarely reach maturity. Outside of growers’ orchards, scientists say, the tree is “functionally extinct.”
LoPiccolo and other researchers at SUNY ESF are growing American chestnut trees in the fields of Syracuse that can withstand that infection: Half of the nuts produced with the genetically engineered pollen will carry DNA meant to fight the blight. The researchers are now ready to sow the seeds in the wild, pushing to become the first in the United States to use gene editing to bring a forest tree back to its former glory.
But first, the project is seeking approval not only from three federal agencies but also from chestnut aficionados concerned about altering the genome of a beloved tree.
Global trade and climate change are poised to make the spread and severity of arboreal plagues and pestilence worse. The hills around Syracuse are silhouetted with pale ash trees slain by emerald-colored borers. Ancient bristlecone pines out West are succumbing to bark beetle outbreaks triggered by rising temperatures. As many as 1 in 6 trees native to the Lower 48 states are at risk of extinction.
Scientists have wondered whether it’s possible to restore forests by raising better trees. Bringing back even a portion of the 2 billion tons of chestnut biomass lost to fungus would not only remake deciduous forests in the east but would also help combat climate change. Long-living and fast-growing, the American chestnut is a powerful sponge for greenhouse gas emissions.
“We’re making a path for saving other tree species, and it might even go beyond trees,” said Bill Powell, director of SUNY ESF’s American Chestnut Research and Restoration Project.
Gaining approval to start planting the nuts, Powell said, would be a “big, big success.” Still, he acknowledged this is something no one has done before — and would require massive effort. His team would also need help to spread blight-resistant chestnuts across hundreds of miles of mountains.
“I always say this is a century project. It’s going to take the general public wanting to plant these trees,” he said.
That’s not a given: Some chestnut lovers are leery of messing with what more than one writer has dubbed nature’s “perfect tree.” And regulators need to give the go-ahead.
“The big public policy question is: Should we bring back forests with genetically modified chestnut trees?” said Edward Messina, director of the Office of Pesticide Programs at the Environmental Protection Agency, one of the agencies weighing approval. “That’s a pretty heavy question.”
The American chestnut showered sustenance onto the forest floor for jays, squirrels, bears and people for millennia. Native Americans fashioned the tree’s bark into wigwams. European colonists chopped its trunks into logs for cabins.
Its straight-grained timber was sought by furniture fabricators and musical instrument makers. Its rot-resistant wood was ideal for the railroad ties, telegraph poles and fence posts that helped connect and carve up the young nation. Its lumber held generations of Americans from cradle to coffin.
The tree served to signal changes in seasons, decorating hillsides with cream-colored petals to begin summer and showering children with chestnuts after they climbed and clubbed its branches in the autumn. Pushcart vendors selling roasted chestnuts on city streets once marked the start of the holiday season.
But by the time Nat King Cole sang of “Chestnuts roasting on an open fire,” the tree had nearly vanished.
Workers at the Bronx Zoo were the first to notice, in 1904, the festering wounds. By the following spring, nearly every chestnut in the park showed signs of infection.
The fungus, brought over on a different species of chestnut tree imported for agriculture, leads to cankers in the tree’s bark. Once an infection girdles a trunk, the circulation of nutrients is cut off. The leaves above droop and die — and the tree is doomed.
The pathogen, called Cryphonectria parasitica, spread in all directions. The crisis prompted Congress to task the U.S. Department of Agriculture with inspecting and quarantining agricultural imports.
But the 1912 law came too late for the species. Within a few decades, the pathogen nearly eradicated the species from North American forests.
‘We got to try this out’
For years, horticulturalists bred American chestnuts with the trees’ Asian cousins, which carry a natural hardiness to the fungus. But with hundreds to thousands of genes involved, efforts at producing a hybrid that flourishes in the wild have met only middling success, according to Jared Westbrook, a geneticist and director of science at the American Chestnut Foundation, a nonprofit organization seeking to rescue the tree.
“We’ve come to this existential realization, we need an additional source of resistance so these trees can survive,” he said.
The setbacks prompted Herb Darling, co-founder of the foundation’s New York chapter, to approach Powell about turning to biotechnology to resurrect the species.
A professor of forest pathology in Syracuse, Powell had written his PhD dissertation on chestnut blight. In the 1990s, while paging through summaries of recently published papers in his office, he had an aha! moment: He spotted a gene that could protect the chestnut.
“I immediately called my colleague, Chuck Maynard, and said, ‘We got to try this out.’ ”
The fungus infecting chestnut trees thrives by secreting a chemical called oxalic acid, which kills cells and allows the pathogen to feast on the dead tissue. But many other plants, including bananas, strawberries and wheat, avoid that fate by producing an enzyme called oxalate oxidase that breaks down the toxin.
By 2014, Powell and Maynard successfully added the wheat gene to chestnuts and were growing infection-resistant trees. The pair dubbed one line Darling 58, in honor of Herb.
At the orchard in Syracuse this June, a team working with Andy Newhouse, a biologist and assistant director of the restoration project, had dug hooks into their tiny trunks to intentionally infect them with the fungus.
The results were dramatic: On the tree carrying the disease-resistant gene, a gray, dime-size sore swelled up at the site of the quarter-inch incision — an infection from which the tree would recover.
In the tree without the gene, a rust-orange depression spread halfway around the trunk. “It’s killing the tree,” Newhouse said. “Almost certainly it’s going to be girdled within another month. And everything above here will be dead.”
Previous inoculation experiments showed that cankers on ordinary American chestnuts grew to quadruple the length of those on their counterparts with genetic material transferred from wheat.
“Making a transgenic tree — I hate to say it like this, but it isn’t that hard,” Newhouse said. The most difficult hurdle for Darling 58, he said, is winning regulatory approval.
‘Truly a cautionary tale’
To distribute Darling 58 in the wild, the restoration team is awaiting a decision from three federal regulators — a process that began in 2020.
The EPA is reviewing how the transgenic tree’s enzyme will interact with people and the woodland environment. The Food and Drug Administration is evaluating the nuts’ nutritional safety. And the USDA’s Animal and Plant Health Inspection Service is reviewing how the tree may affect insects and other plants.
“We were even told 10 years ago, before we started this process, that it probably wouldn’t be realistic for our little university research project to do this,” said Newhouse, who is responsible for guiding Darling 58 through the regulatory process.
The group has done its own testing on both regular and transgenic chestnuts, comparing effects on bumblebees pollinating their flowers, insects feasting on their fresh leaves and frog tadpoles gobbling up their decomposing litter.
“There was no difference,” Powell said.
But saving a species — especially with genetic engineering — is as much a public relations battle as it is a scientific quest. Critics say releasing the transgenic tree is akin to running a massive and irreversible experiment in the wild.
During the USDA’s public comment period, hundreds of people urged the agency not to approve Darling 58, arguing that not enough is known about the risks it poses. Chestnuts can live for centuries, they note, but the transgenic trees have only been tested for a few years.
Anne Petermann, executive director of Global Justice Ecology Project, which helped organize the campaign against Darling 58, is worried the project will lead to more commercial use of transgenic trees, to produce paper and lumber. She noted biotech firms hoping to make greater use of genetically modified organisms have helped fund SUNY ESF’s work.
“There are studies coming out weekly that show just how much we don’t know about forest ecosystems,” she said.
Some people cite past efforts to save the chestnut as a reason their concern is justified. In the 1910s, for instance, Pennsylvania foresters told landowners to chop down healthy trees in a vain effort to stop the spread of the fungus, a practice that may have inadvertently exterminated native chestnuts with blight tolerance.
“The story of the American chestnut is truly a cautionary tale,” said Donald Edward Davis, a founding member of the Georgia chapter of the American Chestnut Foundation and author of “The American Chestnut: An Environmental History.” “And because of that, I really think the public should be more careful about endorsing, just carte blanche, the transgenic approach.”
Davis left the foundation after it threw its support behind the SUNY ESF project in 2016. So did Lois Breault-Melican and Denis Melican, a wife and husband who served as board members of the Massachusetts and Rhode Island chapter.
Some growers, the couple said, have given up too soon on trying to pick out blight-resistant American chestnuts and breed them with their Asian counterparts.
“We don’t need genetic engineering to bring the chestnut back,” Melican said. “They are coming back. All that’s necessary is patience.”
But Powell countered that crossbreeding transfers far more genes between species. “Genetic engineering is actually a less-risky procedure than a lot of things that we’ve done in the past,” he said. “We are very precise. We’re only moving one, two — just a small number of genes into the tree.”
Powell hopes his work spurs similar efforts among geneticists.
“It’s going to spark a lot of other research on trees that people basically wanted to do but couldn’t do because they had that brick wall in front of them,” he said.
Already, Powell’s team is investigating ways to insert blight-resistant genes into chinkapins, a tree closely related to American chestnuts, and to engineer elms that can resist elm yellows, a bacterial disease with no known cure.
At Purdue University, researchers have attempted to tweak the genes of ash to survive the emerald ash borer, a beetle from Asia that has destroyed tens of millions of trees across 30 states since first identified in Michigan in 2002.
With advancements like CRISPR, a Nobel Prize-winning gene-editing tool that is faster, cheaper and more precise than its predecessors, more opportunities will only open up for genetic engineers.
For now, Darling 58 winds its ways through federal bureaucracy.
“This particular review has taken us a bit longer,” said USDA spokesman Rick Coker, noting the agency still needs to publish draft reviews, gather feedback and finalize documents. The researchers expect the three agencies to make a final decision by next summer.
Here in Syracuse, yards away from his tree experiment, Newhouse stepped into a field of knee-high saplings. The tiny oaks, hickories, pines and chestnuts here were not planted in neat rows, unlike in other parts of the research station. Instead, they were sown seemingly at random, a vision for how closed Appalachian coal mines might be reseeded in the future. Chestnuts can thrive in poor, rocky soil left in quarries.
If there’s any chance of returning the American chestnut to its former heights, thousands of acres need to be reclaimed. Many factors could complicate restoration. The fungus could evolve. Other diseases may take hold. Rising temperatures are poised to shift its range north.
“The scale of the former range of American chestnut is so huge, it’s intimidating to think about what that will look like,” Newhouse said. “And it won’t happen in our lifetimes.”
Ultimately, public input will be integral to whether restoration can go forward, said Messina, the EPA official. His team will weigh the benefits of the project, “which I can argue there are many, with any identified risks.”
“This case sits right at the intersection of cutting-edge science and public policy considerations,” Messina said in a video call. Still the question remains, he added: “Just because we can do something, should we?”