The American Chestnut: Restoring an Ecosystem Through Genetic Engineering
The functionally extinct American chestnut tree is undergoing a revival process through backcross breeding and genetic engineering to create a blight-resistant tree.
Have you ever wondered what your neighborhood looked like before humans settled there? No houses, lots of wildlife, lots of trees, probably— but if you live on the East Coast, there were different trees than those you see today.
The American chestnut tree used to cover the East Coast from Ontario to Alabama, from the Atlantic to the Mississippi. American chestnuts were behemoths, reaching as high as 100 feet tall and more than 10 feet across. In some forests on the East Coast, they made up more than half of the trees present. Considering how widespread the trees were, it’s no surprise they were a staple of American industry.
The American chestnut was known as the tree that took care of Americans from “the cradle to the grave.” Cradles, coffins and general household furniture were crafted from American chestnut wood. The house itself, or perhaps only its foundation, would be made from the American chestnut, as its comparatively light weight and rot-resistance made it a favorite of the lumber industry. It was used for railroad ties, telephone poles and in the tanning industry. Moreover, chestnuts dropped by the tree would be used as fodder for livestock, roasted over a fire at Christmas, or even made into flour. It was truly an American tree, acting as a major player in the economy, ecosystem and culture of the East Coast.
And then it disappeared.
In the late 1800s, Japanese and Chinese chestnuts were imported to North America. They brought with them chestnut blight, or Cryphonectria parasitica, a fungus which the Asian chestnuts have a genetic immunity toward.
The American chestnut was less fortunate. Without the immunity enjoyed by its Asian counterparts, the blight ravaged the American chestnut population. It spread through the forests of the East Coast, reducing chestnut trees to nothing but roots, and in less than 50 years, the American chestnut was functionally extinct.
Of course, functionally extinct is different from wholly extinct. Wholly extinct species, like the dodo bird, are completely dead. The American chestnut doesn’t fall into that category. Firstly, the blight targets the trunk and branches of the tree, while the roots survive. In this manner, a tree can sprout over and over, although it can never grow for more than a few years before succumbing to the blight again. Secondly, some specimens of the American chestnut are still alive and well, and that means there’s still hope for the “redwood of the east.”
While efforts to restore the American chestnut have been underway since before it was functionally extinct, it wasn’t until 1983, when the American Chestnut Foundation (TACF) was established, that there was a unified movement dedicated to bringing the American chestnut back to life. Since then, TACF has been working with a variety of collaborators and methods to create a blight-resistant chestnut tree, one that would be safe to reintroduce to the wild. They’ve made progress, but it hasn’t been smooth sailing.
TACF began trying to create a blight-resistant tree by backcross breeding the American chestnut with Chinese and Japanese chestnuts. They would cross an American chestnut with an Asian one, cross the offspring with each other, and so on until a tree was produced that was almost entirely American, with the hope that only the genes conferring blight resistance would be present. While this method has shown some progress, it has a couple of drawbacks.
For one, chestnut trees won’t bear fruit for the first three to five years of their lives. In terms of plant breeding, especially with a specific purpose, that’s an age. Moreover, “…there are too many genes involved in blight resistance to reliably capture them all in individual trees through backcross breeding,” TACF field worker Bruce Levine told Montgomery Magazine.
The mechanism by which blight resistance functions is too complicated to easily capture in one tree, and researchers can’t control which genes are passed on to each generation. Therefore, whether or not a tree receives even partial resistance is entirely up to chance.
Fortunately, there are other methods available. TACF and the State University of New York College of Environmental Science and Forestry (SUNY-ESF) collaborated to use gene editing to produce a blight-resistant American chestnut. This involved using CRISPR to insert a blight-resistance gene from wheat into the chestnut genome, creating a transgenic, blight-resistant chestnut. This method is faster than backcross breeding and gives the scientists far more control. However, as recent events have proven, it’s not without its downsides.
The strain of transgenic American chestnuts created by SUNY-ESF is called the Darling line. The wheat gene used to confer blight resistance was placed in different locations in the genome to create different varieties in the Darling line. One of these varieties, Darling 58, showed significant blight resistance when compared to wild trees. Following this success, TACF and SUNY-ESF submitted petitions to USDA APHIS, the EPA, and the FDA to deregulate Darling 58, allowing it to be planted in the wild. Everything seemed to be going well.
Unfortunately, while this process was underway, collaborators at the University of New England and the University of Maine noticed that some of the Darling 58 specimens were exhibiting strange symptoms, including stunted growth and increased mortality. Upon investigation, they discovered that some of the specimens were not Darling 58, but Darling 54. Sometime during the process of seedling production, a few specimens had been mislabelled. This means that the data gathered from the field trials is no longer reliable, and more research needs to be done on both the Darling 58 and the Darling 54 before moving forward with deregulation.
As a result of this mixup, and the fact that SUNY-ESF had not communicated this information directly, TACF withdrew their support from the project. Furthermore, because the data produced by the field trials is now in question, SUNY-ESF was required to pause their application for deregulation until they have reliable data to support their claim that the Darling 58 is blight resistant with no side effects and will cause no environmental damage.
Reactions to this failure have been mixed. Andrew Newhouse, director of chestnut restoration at SUNY-ESF, believes that the concerns surrounding the Darling line are overstated. “We are very interested in moving forward and doing good science, and we don’t think that completely pulling the application is justified,” he told The Washington Post. He and his team are amending their Darling 58 approval documents and intend to proceed with their application as soon as they clarify the data surrounding the line. “We haven’t seen risks, we haven’t seen harm to other organisms, and we think it’s very important to keep studying this, to keep learning about it,” Newhouse added.
On the other hand, opponents of the Darling 58 line seem to have expected some kind of wrench in the application process. Anne Petermann, international coordinator for The Campaign to Stop GE Trees and co-founder of the Global Justice Ecology Project, told Breaking Green, “We were quite surprised [when TACF withdrew their support for Darling 58], but we were not surprised that the trees didn't work.”
As evident from the name, The Campaign to Stop GE Trees opposes the use of genetic engineering in trees due to the risk of “contaminating native forests, damaging ecosystems and harming communities.” They view the concerns surrounding Darling 58 as inevitable and are glad that the deregulation process has stalled.
The issue with this attitude is that it focuses on the method by which a blight resistant tree is produced. If backcross breeding produced a blight resistant American chestnut, The Campaign to Stop GE Trees would be okay with it, although it would essentially still be a transgenic species, as it would contain a gene from a Chinese or Japanese variety.
Concern for the existing ecosystem is admirable, and it’s understandable that some people have hesitancies around introducing or reintroducing any tree into an existing ecosystem. We do have a duty to limit the damage we do to the natural world. That said, we also have a duty to repair the damage we have already done. An entire ecosystem was destroyed when chestnut blight was introduced to the United States. Introducing a genetically-engineered chestnut could be the first step to restoring the natural ecosystem, and refusing on the basis of distrusting a well-documented and entirely testable technology is not only foolish, it’s irresponsible.
Best,
Grace for the Don’t Count Us Out Yet Team