American chestnut trees, which once numbered as many as four billion and stood twelve stories tall, were almost entirely wiped out by a fungus, called "blight" that first appeared in 1904. It was, of course, imported; the fungus hadn't existed in America until Asian chestnut trees were brought here. Those chestnusts were not only edible, they were a staple. In fact, if we still had those 4 billion trees today, they could provide 100% of the caloric needs of everyone in the USA.
Well, it turns out that scientists have discovered that wheat has a gene that's resistant to the fungus, and so they've inserted that gene into a sample of remaining American chestnut trees. And sure enough, it confers resistance there as well:
Thanks to a group of scientists at the State University of New York College of Environmental Science and Forestry, headed by Bill Powell and Chuck Maynard, it could happen. On Nov. 4, they announced that they had bred a blight-resistant American chestnut by introducing a gene from wheat.
Blight kills trees by producing oxalic acid. Wheat has a natural defense against oxalic acid; the plant can break it down into benign components. It turns out that a single gene is responsible for that function, and inserting that single gene into the American chestnut genome made the tree resistant.