GMO trees could rescue American chestnut from invasive fungus | Ars Technica

Is the US ready for a brave new backyard?

It’s estimated that there were once four billion American chestnut trees in the eastern US. Now there are almost none.
Oak Ridge National Lab

The relationship between the US public and genetically modified organisms is a bit ambiguous. Efforts to label GMO foods were defeated in California, while some Hawaiian islands have banned the planting of GMO crops. But for most Americans, these issues remain pretty abstract.

That may change thanks to work taking place in upstate New York. There, scientists are planning the return of an American icon in a genetically modified form. And if all goes according to plan, ten thousand GMO chestnut trees could be ready to plant in as little as five years. People could find them in parks and playgrounds and even in their neighbors’ yards.

The American chestnut was once a major feature of the Appalachian forests, with its range covering the entire East Coast. But it fell victim to an invasive species: a fungal blight has pretty much wiped out the species in its native range. A few nearly dead trees sporadically send out shoots, and some survivors outside its normal range are the only reasons we’re still able to grow any American chestnuts.

Efforts to restore the tree initially focused on interbreeding with an Asian chestnut that’s resistant to the fungus. But resistance turned out to be complex, conveyed by a mix of seven different genes. That’s made it much harder to produce something that’s both resistant and primarily carries the American chestnut genome. The long generation time for trees has made matters worse.

Researchers at the SUNY College of Environmental Science and Forestry, however, thought it might be easier to engineer resistance. The fungus (Cryphonectria parasitica) that infects the trees causes many of its lethal effects through a chemical called oxalic acid. Many plants carry genes that break oxalic acid down to simpler chemicals. Why not simply insert one of these genes into the American chestnut?

The researchers started with a gene that’s already been field tested in humans: the wheat version of oxalate oxidase. To get it into chestnuts, they inserted it into a special piece of DNA carried by a bacteria that infects plants. When these modified bacteria were given a chance to infect chestnut cells, instead of inserting their own DNA, they’d now insert the wheat gene, providing the American chestnut with a protection it currently lacks. The chestnut cells could then be treated with a combination of chemicals that trigger them to act like an embryo, causing them to grow roots and a stem.

By 2010, the efforts had made it to the point where the lab was growing its first generation of transgenic seedlings. And the tests were promising. Although these plants didn’t resist the fungus as well as the Asian chestnut, they held up far better than an unmodified American chestnut. And the researchers quickly—at least as quickly as trees would allow—confirmed that the inserted genes could be passed on to the next generation.

But performing these experiments was a bit more complicated than normal plant breeding might be. The flowers that were fertilized with pollen from the genetically modified plants had to be placed in plastic bags—in part to keep other pollen out, but in part to contain the genetically modified pollen. As the flowers matured into chestnuts, they had to be enclosed in wire mesh: "larger bags made of aluminum window screen were secured around each pollination bag to prevent animal disturbance and to keep the resulting nuts contained."

In addition, the work contained a metabolite analysis; essentially, the researchers showed that the nuts produced by the GMO trees aren’t chemically distinct from unmodified chestnuts. This is a key test for something that may eventually end up being eaten, either knowingly or unknowingly.

So, as far as these results are concerned, this strain of chestnut is ready for restoration to the tree’s previous habitat. But as far as the US as a whole is concerned, it’s not there yet. Before it can be planted outside of a controlled research plot, the trees will have to be approved by the US Department of Agriculture, the Environmental Protection Agency, and the Food and Drug Administration. The process of obtaining those approvals is expected to take at least five years. The researchers expect they can have as many as 10,000 of the trees ready to plant by the time the approval occurs.

But there’s still the matter of public approval. One place these trees might be planted is on public parkland—the areas of protected forest that preserve the habitats where it once thrived contain many state parks and two national ones. But the mission of these parks is generally to preserve the natural ecosystem, and it’s safe to assume that some people will object to a transgenic plant being introduced to a natural ecosystem.

The other place the trees are likely to go is private properties. The research is funded in part by The American Chestnut Foundation, which is enthused about returning the species to the wild. Presumably, some of its members will be just as enthused about putting the trees in their yards. Whether their neighbors will be equally enthused is debatable.

So far, the debate within the US about the role of genetically modified organisms has been relatively muted compared to that in Europe. And, fortunately, the subject has not become politically polarized; concern about the risks posed by the technology are similar across the political spectrum. But that data also makes it clear that a lot of people do perceive a risk, despite decades of study and use that haven’t revealed any problems.

The use of GMO crops is likely to continue to expand—a recent analysis of global data suggests that GMO crops raise yields, lower pesticide use, and increase farmers’ income. But for most citizens, their use as crops is an abstraction, something that happens far away. It may be that the transgenic chestnut will be the first time many people are faced with seeing a GMO plant up close—and have to decide if they want one in their backyard.

Plant Science, 2014. DOI: 10.1016/j.plantsci.2014.04.004 (About DOIs).

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