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article imageEssential Science: Small molecule, big future in food security

By Tim Sandle     Mar 20, 2017 in Science
This week’s Essential Science looks at how scientists are using molecules to stop a corn-infecting fungus from producing a potent toxin and running crops. The fungus poses a major risk to food security, especially in the developing world.
The new research rests on RNA molecules. Ribonucleic acid (RNA) is a polymeric log-chain molecule that is essential in various biological roles. These include coding, decoding, regulation, and expression of genes. It is a nucleic acid like DNA. RNA molecules are involved in protein synthesis and sometimes in the transmission of genetic information.
The fungi of concern are certain species of Aspergillus and these produces toxins called aflatoxins. Aflatoxins are a specific type of mycotoxin (‘toxins from fungi’) and form part of a family of toxins commonly found on agricultural crops like maize (corn), peanuts, cottonseed, and tree nuts. Build-up of the toxin by eating contaminated food can be very dangerous. Children are particularly affected by aflatoxin exposure, where a concentration over time can lead to stunted growth, delayed development, and liver damage. In addition, aflatoxins have received greater attention than any other fungal toxins because of their demonstrated potent carcinogenic effect (where cancer has been shown to occur with laboratory test animals following high exposure to the toxins).
Permitted levels of aflatoxin on foods vary in different parts of the world. The U.S. Food and Drug Administration (FDA), for instance, has action levels for aflatoxin present in food or feed as 20 to 300 parts per billion. In some parts of the world, while limits may be in place, no testing is undertaken due to the logistics and costs required to enable effective quality control to take place.
Close up of a fungus
Close up of a fungus
The primary fungi of concern are Aspergillus flavus and Aspergillus parasiticus. The organisms are abundant in warm and humid regions of the world. These are saprotrophic fungi (meaning they obtain their nutrients by processing of dead or decayed organic matter) and worrisome pathogens. With A. flavus contamination, this causes ear rot in corn and yellow mold in peanuts either before or after harvest. The infection can occur at almost any time: preharvest, postharvest, during storage, and during transit. However, it is more common for the pathogen to originate while host crops are still in the field; however, symptoms and signs of the pathogen are often unseen. The big risks with postharvest contamination relate to situations when crop drying is delayed, or when water is allowed to exceed critical values as the crop is being store. Damp and moist conditions help to accelerate mold growth.
Of all the different crops, corn remains at greatest risk from contamination with the toxin. The seriousness of this is affected by the processing steps involved. Some forms of corn processing present a lower risk, such as with making tortillas. This is because the process employs alkaline conditions and oxidizing steps. However, other corn-based products, where there are few processing steps, are at risk. This is where the new research comes in: creating more resistant corn.
Aspergillus fumigatus is a fungus of the genus Aspergillus  and is one of the most common Aspergillu...
Aspergillus fumigatus is a fungus of the genus Aspergillus, and is one of the most common Aspergillus species to cause disease in individuals with an immunodeficiency.
US Department of Health and Human Services
The development of the new approach for protecting corn comes from the University of Arizona. The development involves the use of transgenic corn plants that can produce small RNA molecules which function to prevent fungi from producing aflatoxin. A transgene is a gene or genetic material that has been transferred naturally, or by any of a number of genetic engineering techniques from one organism to another by a technique called "transgenesis". In trials transgenic corn plants infected with the fungus were able to suppress toxin levels below detectable limits.
The new research has been funded by the Bill and Melinda Gates Foundation. The starting basis was to see if a naturally occurring biological mechanism (the RNA) could be used as a weapon against the fungal toxin. This was shown to be so using a method called Host-Induced Gene Silencing. This revealed that during the time of infection, the plant that becomes infected exchanges small nucleic acid molecules with the invasive fungus.
Some ears of unusually colored and shaped maize from Latin America.
Some ears of unusually colored and shaped maize from Latin America.
Keith Weller, USDA
This led to the development of an engineered genetic construct, added into the corn, that can pass RNA into the fungus when it infects the corn plant. This genetic transfer effectively shits down the ability of the fungus to pass on its toxin. This has led to the creation of corn containing small RNA molecules found in edible kernels. The fungus is blocked from producing the toxin as a result of RNA interference, which blocks the fungus’ own RNA that code for the enzyme required for toxin production. The highly specific mechanism involved is one reason for the success of the project.
Maize in Mexico.
Maize in Mexico.
ETC Group
Test on the corn indicate that the transgenic versions of the corn plants come with no undesired side effects. This was evaluated in terms of comparing differential gene expression between the transgenic and the non-transgenic kernels. This means the modified corn plants are just like any other unmodified corn plant, as far as a farmer or consumer is concerned.
The research into the molecule is published in the journal Science Advances, under the title “Aflatoxin-free transgenic maize using host-induced gene silencing.”
Essential Science
This article is part of Digital Journal's regular Essential Science columns. Each week Tim Sandle explores a topical and important scientific issue. Last week the subject was neuroscience and social media, looking at what happens to our brains when we decide whether or not to share an article or video. The results are illuminating in terms of why we share one article but decide not to share another. The previous week we embraced futurism and considered a new technological path to creating an unlimited supply of ‘green’ energy via nuclear fusion.
More about Food security, molecules, Rna, Corn, Fungi
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