Can a transgenic chestnut restore a forest icon?

American chestnuts, towering 30 meters or more, once dominated forests throughout the Appalachian Mountains. But in the early 1900s, a fungal infection appeared on trees at the Bronx Zoo in New York City, and then spread rapidly. The so-called chestnut blight – an accidental import from Asia – releases a toxin that girdles trees and kills everything above the infection site, though still-living roots sometimes send up new shoots. By midcentury, large American chestnuts had all but disappeared. 

In 1990, SUNY ESF tree geneticists William Powell and Charles Maynard (now retired) decided to try to create resistant chestnuts with the then-new technology of genetic engineering. Eventually, they inserted into the tree's genome a wheat gene that codes for an enzyme called oxalate oxidase, or OxO. It breaks down the oxalic acid the pathogen releases, which is what kills the trees. “We're basically taking the weapon away from the fungus,” Powell says.

It didn't work at first. Then, the scientists changed the wheat gene's promoter sequence to cause OxO to be expressed at high levels. In 2014, they reported that a GM tree named Darling 58 both resisted blight infection and transmitted resistance to its offspring. Subsequent tests showed that it produces nuts indistinguishable from those of native trees, Newhouse says. And its pollen, flowers, and decaying leaves don't harm bees, beneficial soil fungi, or tadpoles that hatch in pools on the forest floor.

But the request to release it is likely to face a lengthy regulatory road. The United States, China, and Brazil have approved some transgenic trees for use in fruit orchards, biofuel plantations, and afforestation projects. But like GM crops and animals, GM trees are controversial, and ethical and ecological concerns are heightened because the chestnut trees would grow wild.