Genetic engineering may be key to chestnut revival

Chestnuts Isolated On A White BackgroundThroughout the 1800s, chestnut trees were a major source of food as families would use the nuts in everything from bread to pickles, to preserves and cream pies. However, that changed in the early 1900s when a plague known as blight, decimated American chestnut trees. This deadly fungus came to the U.S. on the much smaller and fungus-resistant Chinese chestnut trees and wiped out nearly four billion American chestnut trees seemingly overnight.

Because of this, scientists have been researching ways to bring the American chestnut tree back and now researchers at the State University of New York College of Environmental Science and Forestry (SUNY-ESF) may have an answer.

Over the course of a 25-year study, the researchers have used genetic engineering and bestowed the chestnut with a highly protective gene that is proving to be resistant to blight. This gene has evolved on its own in bananas, cocoa, wheat and barley, and so far the transgenic seedlings are proving to be at least as resistant to blight as the hybrid or Chinese chestnut trees.

As stated in a recent article, this isn’t the first attempt to save the American chestnut. Since 1983, the American Chestnut Foundation has been carrying out a restoration project —selectively breeding a blend of resistant Chinese chestnuts with vulnerable American chestnuts, hoping to transfer enough genes from the Asian trees to create a blight-resistant American tree with the favored height and strength.

They have been slowed, though, the article states, by the fact that a panoply of seven genes protects the Asian tree, and all must transfer. Also, some chestnuts only tend to succumb to blight after five or 10 years, so the foundation must grow the latest generation of trees—which are only 1/16th Chinese—for at least a decade before they can feel confident enough to release seeds to the public.

What is different with the project at SUNY-ESF, however is that these scientists transplanted the gene that wheat, barley, cocoa and some fruits already use to protect themselves against fungus into chestnut embryos. The gene makes an enzyme to degrade an acid produced by the fungus, rendering the fungus harmless. The scientists then harvest the few cells that took up the gene, and used those cells to grow a new embryo, nourishing it with all the nutrients it needs to become a “plantlet” or seedling.

According to the article, the first generations of plantlets proved hardy but not fully immune, so the scientists replaced a genetic “dimmer” switch inside the gene to turn it up so it would produce more enzyme. Now, the latest generation of plantlets have proved more resistant than American chestnut seedlings and hybrid seedlings.

“We have about 1,000 plants now in the field,” researcher Andy Newhouse said in the article. “The best ones are about six feet tall and two or three years old, and we’ve shown that the gene does transfer to the next generation,” Newhouse added.

The ultimate plan is to plant about 10,000 transgenic seedlings and grow them big enough to produce enough pollen to pollinate other “wild” and vulnerable American chestnuts.

However, not everyone welcomes the idea of transgenic chestnuts. Some organizations have voiced concern because little is known about the American chestnut’s normal ecological interactions, which are likely to be specific to a site or region.

Allison Snow, a plant population biologist at Ohio State University, said in the article that it’s harder to evaluate GMO trees for possible ecological risks compared to other crops because trees aren’t domesticated and live for decades.

“In the case of a very rare species like the American chestnut, I can’t think of ecological problems that might come up because of transgenic blight resistance,” Snow said in the article.”It seems unlikely that these trees could become invasive or harmful to other species. But I would like to see published studies showing that these assumptions are correct.”

Newhouse said he wants to reassure those who worry about the transgenic chestnuts.

“This gene is a common adaptation in nature,” he said in the article. “It’s so widespread already it’s highly unlikely to do any harm. But just to be sure, we carried out metabolomic tests to examine changes in sugars, amino acids, and fatty acids. The changes we found were minor and actually less than natural variation between Chinese and American chestnuts.”

Newhouse estimates that in about five years, the transgenic tree will be approved, and released in the “wild.”

Until then, however, chestnut lovers must continue rely on nuts produced only seasonally by specialty growers who have groves of either Chinese or Dunstan hybrid trees.

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