Researchers at the University of Arizona have found a promising way to prevent the loss of crops to a fungus, offering the potential to improve food security, especially in developing countries. The team’s approach uses transgenic corn plants that produce small RNA molecules that prevent fungi from producing aflatoxin, highly toxic substances that can render an entire harvest unsafe for human consumption even in small amounts. The study, published in Science Advances, suggests that transgenic corn plants infected with the fungus suppressed toxin levels below detectable limits.
Funded by the Bill and Melinda Gates Foundation, the researchers set out to study whether a naturally-occurring biological mechanism called RNA interference could be used as a weapon against the Aspergillus toxin. That approach, called Host-Induced Gene Silencing (HIGS), builds on previous work by other researchers who discovered that during the infectious process, the host plant and the fungus exchange small nucleic acid molecules.
The researchers infected corn plants with Aspergillus and let them grow for one month. While untreated control plants were found to harbor toxin levels between 1,000 and 10,000 per billion, toxin levels were undetectable in the transgenic plants. The team took the project a step further and investigated overall gene expression in kernels to see if the transgenic corn plants come with undesired side effects. This involved co-author Rod Wing’s laboratory, also of the UA’s School of Plant Sciences, to compare thousands of RNA transcripts between the nontransgenic control kernels and transgenic kernels. The team did not find a single significant difference in terms of differential gene expression between the transgenic and the non-transgenic kernels.
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. 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.