Genetically Engineering an Icon: Can Biotech Bring the Chestnut Back to America's Forests?

In the 20th century, a blight killed off four billion of these towering trees. Now, new research shows that a gene, taken from wheat, provides resistance.
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Lumberjacks stand besides old-growth chestnut trees in North Carolina around 1909/1910. (Forest History Society, Durham, North Carolina)

"The forests of America,"John Muir wrote in The Atlantic in 1897, "... must have been a great delight to God; for they were the best he ever planted." Muir didn't know it yet, but by the time he wrote those words, the king of the eastern forests, the American chestnut tree, was already doomed. An interloping fungus had arrived at America's shores two decades earlier, and it would soon make short work of this then-common species. In less than a century's time, it killed off an estimated fourbillion of these towering trees.

Now, for the first time since the die-off, there is real hope. Researchers at SUNY's College of Environmental Science and Forestry have been trying to build a better American chestnut, one that would be resistant to the blight, and there's reason to think they've succeeded. Such a plant could repopulate the vast region of the eastern United States in which the tree was once found.

It's hard to overstate what a dramatic reversal this would be. Chestnuts were once one of the most abundant trees in the eastern United States, making up about 25 percent of the mature timber. Today, there is a list on Wikipedia entitled "surviving specimens," and it is not long.

The trouble began in the 1870s, when Americans began importing chestnuts from Japan to New York. The Japanese trees were shorter, making for a better orchard crop, as their nuts could be more easily reached. Unfortunately, those trees harbored Cryphonectria parasitica, a fungal blight to which they were resistant, but to which the American variety was highly susceptible. The fungus would attack a tree at a wound and then spread beneath its bark, releasing a toxin known as oxalic acid that would poison the tree and reduce it to a mere stump that would occasionally send out shoots, but could never grow tall. The blight was discovered in 1904 in what is now the Bronx Zoo by a scientist named Hermann Merkel. Within five decades of that date, the fungus had spread across the entire range of the American chestnut, from Maine to Mississippi.

 

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American Chestnut Foundation

Since the blight's discovery, countless efforts have been made to control the blight or somehow re-instate the trees. Early on, before it had spread too far, people tried cutting firebreak-like gaps into forests, such as a mile-wide chestnut-free zone etched into Pennsylvania -- but the fungus lived on oaks too (though it did not kill them) and made its way across the divide just the same. In more recent decades, scientists have tried cross-breeding the tree with its Asian counterparts, hoping to create a variety that is as American as possible, while retaining the Asian resistance. But though they've made some progress, none of those trees have gained full resistance.

The genetic engineering effort alone has gone on for more two decades, researchers at SUNY's College of Environmental Science and Forestry have been trying to build a better American chestnut, one that would be resistant to the blight.

"At that point, genetic engineering of trees was really in its infancy," William Powell of the SUNY lab told me. "There were only one or two trees that had been what we call transformed -- had a gene put in."

He and his colleague Charles Maynard had to begin before the beginning, figuring out first how to get new genes into their specimens' genomes, and then they could move on to seeing what manipulations might increase resistance. "I like to tell people we had to build the boat before we went fishing," Powell jokes.

They, along with Scott Merkle at the University of Georgia (no relation to Hermann), began by trying to figure out how they could grow a tree from a single cell, since they would be putting the new genes into just one cell. For whatever reason, chestnuts were a tough nut to crack (no pun intended). "For example," Powell explained to me, "if you were to genetically engineer poplar, you can regenerate whole plants just from leaf tissue." With chestnuts, not so much. Instead, they had to harvest an immature nut, remove the embryo, put it in a special medium that allows it to replicate until they had multiple embryos. They worked for 16 years, developing the techniques that would enable them to actually begin genetic engineering.

In 1997, one of the lab's graduate students attended a meeting of the American Society of Plant Biologists, and brought back a book containing hundreds of abstracts. "I was just looking through it," Powell recalled, "and I came across this abstract, the title of which was Expression of Oxalate Oxidase in Transgenic Plants Provides Resistance to Oxalic Acid and Oxalate-Producing Fungi."

Now that may not sound like much if you don't spend all your days thinking about chestnut blight, but to Powell, it struck a bell in his brain -- oxalic acid is the toxin that chestnut blight produces. "Immediately I thought, well, here's a gene that we could use in the chestnut." That gene came from wheat.

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Rebecca J. Rosen is a senior editor at The Atlantic, where she oversees the Business Channel. She was previously an associate editor at The Wilson Quarterly.

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