Crops all over the world are susceptible to infection by fungi of various Aspergillus species, a fungus that produces secondary metabolites known as aflatoxins. These compounds have been implicated in stunting children’s growth, increasing the risk for liver cancer, and making people more susceptible to diseases such as HIV and malaria.
“Aflatoxin is one of the most potent toxins on the planet,” Schmidt said. “Usually it won’t kill a person outright, but it can make you very sick.”
Schmidt and her team set out to study whether a naturally occurring biological mechanism called RNA interference could be used as a weapon against the Aspergillus toxin.
The modified corn plants carry a genetic blueprint for small RNA molecules, each only about 20 base pairs long, only in the edible kernels, not the whole plant.
“The corn is constantly producing that RNA during the entire development of the kernel,” Schmidt explained. “When the kernels come in contact with the fungus, the RNA moves over into the fungus.”
Once inside the fungal cells, the hairpin-shaped RNA molecules pair up with corresponding target sequences of the fungus’ own RNA that code for an enzyme needed for toxin production, in a process called RNA interference. This causes the toxin production to shut down, but does not in any other way impact the fungus, which continues to grow and live on the corn, albeit harmlessly.
“We wanted to identify why modern tomato varieties are deficient in those flavor chemicals,” Klee said. “It’s because they have lost the more desirable alleles of a number of genes.”
Scientists then identified the locations of the good alleles in the tomato genome, he said. That required what’s called a genome-wide assessment study. There, scientists mapped genes that control synthesis of all the important chemicals. Once they found them, they used genetic analysis to replace bad alleles in modern tomato varieties with the good alleles, Klee said.
Because breeding takes time, and the scientists are studying five or more genes, Klee said the genetic traits from his latest study may take three to four years to produce in new tomato varieties.
This technique involves classical genetics, not genetic modification. “We can make the supermarket tomato taste noticeably better.”