How to grow toxin-free corn

Submitted on Mon, 03/13/2017 - 12:51

Corn genetically engineered to make ninjalike molecules can launch an attack on invading fungi, stopping the production of carcinogenic toxins.

These specialized RNA molecules lie in wait until they detect Aspergillus, a mold that can turn grains and beans into health hazards. Then the molecules pounce, stopping the mold from producing a key protein responsible for making aflatoxins, researchers report March 10 in Science Advances. With aflatoxins and other fungal toxins affecting up to 25 percent of crops worldwide, the finding could help boost global food safety, the researchers conclude.

“If there’s no protein, no toxin,” says study coauthor Monica Schmidt, a plant geneticist at the University of Arizona in Tucson.

Schmidt and colleagues used a technique called RNA interference, which takes advantage of a natural defense mechanism organisms use to protect against viruses. The researchers modified corn to make it produce short pieces of RNA that match up to sections of an RNA in the fungus made from the aflC gene. That gene encodes a key step of a biochemical pathway that the fungus uses to make the toxins. When the corn’s modified RNAs match up with those of the fungus, that triggers Aspergillus to chop up its own RNA, preventing a key protein, and thus the toxin, from being made.

Then, the team infected both engineered and not-tweaked corn with A. flavus, an Aspergillus species that releases the most potent aflatoxins. After allowing the corn — and fungus — to grow for a month, the researchers were unable to detect aflatoxins in the engineered corn. But they consistently measured more than 1,000 parts per billion of aflatoxin in the unmodified corn, and sometimes as much as 200,000 ppb, Schmidt says. In the United States, crops intended for human consumption are used for animal feed or destroyed if they have more than 20 ppb. Contaminated crops unsuitable for humans or animals cost $270 million each year.

In countries that don’t screen for toxins, people eat the infected corn. That can cause vomiting, abdominal pain and even induce coma at higher levels. Long-term exposure to lower levels of these aflatoxins may stunt child development and cause liver cancer.

“It’s not just an economic issue, it’s a health issue,” Schmidt says.

Charles Woloshuk, a plant pathologist at Purdue University in West Lafayette, Indiana, says allowing A. flavus to grow and focusing on preventing it from making the toxin is a good approach. In the past, researchers have unsuccessfully tried to breed fungus-resistant crops to combat aflatoxins. But targeting the fungus that way may drive fungus mutations that allow it to keep infecting crops, Woloshuk says.

RNA interference isn’t without danger either. The specially engineered RNA may go rogue and do things they weren’t intended to do, such as affect kernel development or plant growth. But an analysis of the genetically engineered corn showed that the RNA are sticking to the script.

“That’s a good piece of data,” Woloshuk says.

Other current infection prevention methods focus on airtight storage of harvested corn to keep Aspergillus out. But that’s not effective if corn is infected before it’s picked. Coupling genetically engineered corn, which protects the crop as it is growing in the field, with post-harvest storage techniques would be the best way to prevent Aspergillus from contaminating the corn, Schmidt says.

“This is the first step of showing feasibility, but really it’s about getting it onto consumer plates,” she adds. “I realize that’s a long way down the road, but I hope somebody wants to move it forward.”