Aflatoxin is a well-known global health threat. This poison, produced by the Aspergillus fungus, is common in corn, wheat, rice and many other crops. Hot climates and inadequate storage practices augment the spread of the fungus and its accompanying toxin. It has also proved extremely difficult to eliminate or even reduce. A new gene-based approach could change that.
Exposure to aflatoxin can be life-threatening. A known carcinogen, aflatoxin is tightly linked to liver cancer. Felicia Wu, a food scientist who directs the Center for Health Impacts of Agriculture at Michigan State University, reported that up to a quarter of all liver cancer cases worldwide could be due to aflatoxin exposure. Because it accrues in the liver, the toxin also leads to hepatitis, jaundice and cirrhosis. High levels of the chemical have also been found in the brains, lungs, kidneys and hearts of aflatoxin-poisoning victims.
Aflatoxin threatens not only the health but also the economies of countries worldwide. In the United States, corn containing more than 20 parts per billion of it—that is, 0.000002 percent, the equivalent of 20 drops in the largest gasoline tanker truck—cannot be exported or sold for human consumption in the U.S. Tight restrictions also govern how much aflatoxin can be present in U.S. livestock feed. Managing aflatoxin and other fungal poisons costs U.S. food producers an estimated $500 million to $1.5 billion every year.
Countries in the developing world cannot afford to either test for aflatoxin or discard crops containing it. Corn riddled with aflatoxin may still be eaten or fermented to make alcoholic beverages. “They don’t just discard it as richer countries can,” says Wu. Nuts, dairy products and spices grown—and consumed—in low- and middle-income countries are also frequently contaminated with aflatoxin. In addition to the liver illnesses with which it is tied, aflatoxin is also responsible for stunted growth among children in Africa, India and Southeast Asia, according to a recent World Health Organization report.
Scientists at the University of Arizona may have a solution to the aflatoxin problem: shut off the gene in the fungus that triggers its production.
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To force the Aspergillus fungus to stop making aflatoxin, Monica Schmidt and colleagues at the Arizona Genomics Institute used a technique called host-induced gene silencing, a branch of a broader approach to genetics known as RNA interference. They create a genetic sequence containing the desired fungal trait—that is, an absence of aflatoxin production—and insert that sequence into the corn. That sequence is then transferred to the infecting fungal cell, overriding the genetic code linked to aflatoxin production.
Schmidt and her team grew corn plants with and without the introduced RNA sequence and then injected aflatoxin-producing Aspergillus into all the plants. When they harvested the kernels and measured their aflatoxin levels, they found no aflatoxin in the experimental plants. Corn without the newly introduced RNA sequences had aflatoxin levels of up to 225,000 parts per billion. Schmidt is now studying the feasibility of stopping the growth of the Aspergillus fungus, not just the toxin it produces, by interfering with corn RNA.
Schmidt’s analysis, published recently in Science Advances, revealed no other changes to the corn. “You should still be getting all the nutritional value,” she says. But more tests are needed to confirm that her experimental strain of corn is unaltered aside from shutting off aflatoxin production. Nancy Keller, who studies fungal pathogens at the University of Wisconsin-Madison, also emphasizes the importance of studying the corn outside of a greenhouse laboratory. Regulatory agencies would insist on all this testing before allowing the modified corn to be introduced globally.
“This approach has a lot of potential,” says Keller. But she questions whether it will gain widespread acceptance due to the skepticism surrounding genetically modified organisms, or GMOs. The government bureaucracy and public opinion are significant hurdles for the experimental corn to overcome. Keller wonders if the severity of the health hazards could be enough to overcome the reluctance. “Can people accept something like this because it’s genetically engineered?” asks Keller. “Maybe it’s better to have this new strain and not get cancer.”
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