Researchers found that viral pathogens can quickly evolve to overcome transgenic cassava plants expressing the bacterial weapon CRISPR-Cas9, which could have major regulatory implications.
Geminiviruses are pathogens that kill off crops such as beans, cotton and cassava plants. Past efforts to breed plants that are resistant to infection have not been successful.
One potential method for making plants resistant is by giving them the genes for CRISPR-Cas9, a DNA-cutting weapon that bacteria evolved to fight viral infection. This particular use is very specific to making organisms resistant to viruses and is unrelated to using CRISPR-Cas9 as a genome-editing tool.
A team of scientists in Switzerland, Canada, and Belgium used bacteria to deliver the CRISPR-Cas9 genes to cassava plants. The team aimed to make the plants resistant to infection by a geminivirus called African cassava mosaic virus. Unfortunately, the researchers found that the CRISPR-Cas9 genes didn’t work efficiently enough to combat the viral infection. They also found that the virus was mutating to become resistant to the CRISPR-Cas9 genes, which could make these viruses even harder to combat in future.
“It wasn’t completely unexpected,” said lead researcher Hervé Vanderschuren, based at the University of Liège, Belgium. “If you select plants that are naturally resistant to viruses, you see the emergence of viruses that can circumvent this resistance.”
Published in Genome Biology, the discovery of these resistant viruses reveals a major risk of giving CRISPR-Cas9 genes to crop plants. The researchers suggested that regulatory organizations, already pretty stringent in the EU regarding genetic engineering, should consider this risk carefully in the future.
“CRISPR-Cas is undergoing a lot of hype and it has huge potential in agriculture and human health,” Vanderschuren told me. “But it’s also important to share the limitations.”
With some tweaks to the CRISPR system, Vanderschuren believes that his research team might be able to make the plant’s viral defenses more effective and able to overcome viral resistance to CRISPR systems.
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