In this photo taken Tuesday, Oct. 2, 2012. Richardson Okechukwu, a scientist who studies cassava, inspects plants at the International Institutes For Tropical Agriculture in Ibadan, Nigeria.
Sunday Alamba / AP
The use of gene-editing technology to create virus-resistant cassava plants could have hazardous consequences, warn University of Alberta researchers.Roughly three years ago, Devang Mehta, a postdoctoral fellow in the Department of Biological Sciences, began a study as a PhD student in Switzerland on creating virus-resistant cassava plants.The goal of the research was to make the starchy root vegetable resistant to the devastating mosaic disease, which results in about a 20 per cent crop loss annually.But during the study, researchers from the U of A, the University of Liege in Belgium, and the Swiss Federal Institute of Technology found the virus was instead mutating and becoming resistant.“We concluded that because this technology both creates a selection pressure on the viruses to evolve more quickly, and also provides the viruses a means to evolve, it resulted in a virus mutant that is resistant to our interventions,” Mehta said.He added that that cassava plant is different in that it does not require a seed to be replanted. Instead, a piece of the plant’s stem is cut off to grow new crops, a staple grown in South America, Africa and Asia.“The difference here is usually when a plant goes to seed, the viruses that were in that plant usually do not transmit into the next generation. Whereas in the case of the cassava, because it doesn’t involve a seed in order to reproduce, there is this potential the virus could get carried throughout generations of crops,” Mehta said.Researchers used new gene-editing technology — CRISPR-Cas9 — to try and change the DNA of the mosaic virus in order to stop the spread of the disease in the cassava plant.CRISPR-Cas9 is essentially comprised of two genes, CRISPR being one and Cas9 being another. CRISPR-Cas9 is prevalent in many naturally occurring bacteria, which use the system to defend against viruses.Researchers concluded that the gene-editing technology is appropriate for many different applications where editing the genome of a plant or animal is involved. But when it comes to editing the genome of a virus, there are a new set of characteristics to consider, some of them dangerous.“We discovered that the pressure that CRISPR-Cas9 applied to the virus probably encouraged it to evolve in a way that increased resistance to intervention,” Mehta said, noting his research team is keen to share the results with other scientists who are using the technology to engineer virus-resistant plants so they can quickly detect any similar viral mutations.The paper, “Linking CRISPR-Cas9 interference in cassava to the evolution of editing-resistant geminiviruses,” is published in Genome Biology (doi: 10.1186/s13059-019-1678-3).