The Aspergillus family of fungi is a dangerous food contaminant, thanks to its tendency to produce aflatoxins. These carcinogenic compounds have been linked to stunted growth in children, liver cancer, and immune suppression, which in turn increases a person's vulnerability to conditions like HIV. Now, researchers at the University of Arizona have genetically modified corn plants to fight back, by letting them send "Trojan horse" molecules into the fungus to neutralize its ability to produce the toxins.
Even small quantities of aflatoxin can ruin a large harvest, and the US Food and Drug Administration (FDA) has strict guidelines in place that limit the amount allowed in food to a mere 20 micrograms per kilogram, or 20 parts per billion (ppb). The problem is, in developing countries that limit is much harder to enforce, meaning that aflatoxin levels could soar as high as 100,000 ppb.
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"Aflatoxin is one of the most potent toxins on the planet," says Monica Schmidt, lead researcher on the study. "Usually it won't kill a person outright, but it can make you very sick."
The new technique works by taking advantage of the fact that RNA molecules are passed between the infected corn and the Aspergillus fungus. Knowing this, the UA researchers modified the corn plants' genetic code so it produces hairpin-shaped RNA molecules within the kernel, and when the fungus takes hold, these are sent into it. Once there, these molecules target a particular section of the fungus' RNA, preventing it from producing a certain enzyme and shutting down the creation of aflatoxin.
"When I read about this in the literature, I thought, 'Why can't we make a Trojan horse to shut off that toxin?'" says Schmidt. "We introduced an engineered DNA construct into the corn that passes the RNA into the fungus when it infects the corn plant."
The RNA interference doesn't kill the fungus, but it reduces its toxicity to levels that are safe enough for human consumption. Likewise, after comparing the RNA transcripts of the modified plants to unmodified ones, the team doesn't expect that the changes they made to the corn would have any side effects for the people eating it.
"This corn plant would be like any other," says Schmidt. "The only trait that sets it apart is its ability to shut down the toxin production. It shouldn't have any other effects, but obviously, a lot of downstream testing will be required before it could be grown in the fields."
To test the effectiveness of their technique, the researchers grew several sets of corn plants infected with the Aspergillus fungus, and after a month, tested their toxin levels. A control group, which weren't treated, showed aflatoxin levels of up to 10,000 ppb – traces in the modified plants, on the other hand, were almost undetectable. The team has filed a patent for the technique, which apparently has the potential to be applied to other crops.
The research was published in the journal Science Advances and Schmidt describes the study in the video below.
Source: University of Arizona