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Wheat blight destroys wheat grains and can make those that remain toxic.
Images by Nigel Cattlin / Minden
By Elizabeth Pennisi
the Fusarium The fungus is the ruin of the existence of all wheat producers. Causing wheat scab, also known as head blight, it decimates crops and contaminates grains with a toxin harmful to people and animals. Now Australian researchers have devised a new strategy to combat Fusarium graminearum, the best-known pathogen of wheat scab. In the laboratory, they have used a genome-altering technology called “gene drive” to get rid of the fungal genes that make this pest so toxic.
The new wheat strategy would be the first use of a gene boost to control a pathogen in plants. The findings are “very attractive” to plant health and human health, says John Leslie, a fungal pathologist at Kansas State University. However, gene drives have never been deployed outside the laboratory, and plans to use them to kill mosquitoes and other pests have been controversial.
Wheat crust is a growing problem in North America, Europe, and China. Researchers are struggling to breed wheat resistant to this fungus, with some recent success. Still, “disease management is reaching a crossroads,” says Peter Solomon, a molecular plant pathologist at the National University of Australia.
It takes a lot of time and effort to develop new breeds of wheat. And producing significant resistance to this fungus will likely require the introduction of multiple genes. Even then, complete protection may not be achieved. Meanwhile, the fungus quickly becomes resistant to any chemical treatment, and several countries are beginning to ban the use of these fungicides. For these reasons, Solomon says: “It is important that we not avoid considering new and novel methods of controlling disease.”
So Donald Gardiner, a molecular biologist at the Commonwealth Scientific and Industrial Research Organization in Saint Lucia, Australia, and his colleagues decided to see if they could Fusarium less powerful by using gene boost. The process involves the introduction of DNA into an organism that causes one version of a gene to be passed on to the next generation, but not to another. Ultimately, only the desired versions of those genes remain in the population.
Scientists often use the CRISPR gene editing tool as the gene driver. Here’s how researchers hope to fight malaria: They adapted CRISPR to spread a gene that transformed populations of a malaria-transmitting mosquito in all males so that the species cannot reproduce. Given the many uncertainties about the long-term consequences of unlocking a gene drive, scientists are cautiously proceeding with such work.
Although aware of those concerns, Gardiner and his colleagues still felt a genetic drive to detect wheat crust was worth exploring. His intention was to get rid of three Fusarium genes that make the pathogen highly infectious and that the infected grains are toxic, all while leaving the fungus intact in terms of DNA.
They found that CRISPR did not efficiently spread harmless versions of these genes. But a gene in another fungus, what Gardiner calls a natural genetic boost, proved to be up to scratch, more efficient than CRISPR, and easier to work with.
Gardiner and his colleagues linked that gene to harmless versions of the three specific genes. Once in FusariumThe gene-driving gene killed the sexually produced spores that killed off the original versions of specific genes. Therefore, the harmless versions were preferably transferred to the next generation. Those later generations were less able to cause wheat scabies, but were otherwise no different than typical Fusarium, the team reports in a preprint published this month on bioRxiv.
“It’s kind of like replacing a couple of sentences in the middle of a big book with unrelated text,” says Gardiner. In just three generations, the three virulent genes disappeared entirely, he and his colleagues report. “We believe that the technology should be applicable to many other economically important pathogens,” says Gardiner.
Others are skeptical. “It is a new idea, but not a practical one,” says Caixia Gao, a plant biologist at the Chinese Academy of Sciences in Beijing. She thinks nothing Fusarium Deprived of their virulence, genes could survive in nature and overcome unaltered versions of the fungus or other Fusarium species. “The consequences will be that other pathogens can dominate,” he says, and the disease would still be a problem.
And Leslie emphasizes that many mushrooms, including some types of Fusarium, rarely or never reproduce sexually, which is a prerequisite for a gene-driven control mechanism to function. Furthermore, “developing field tests will be very important and probably difficult to design,” he adds. The team will have to demonstrate that the genetic boost is effective in reducing the wheat scab under natural conditions, Leslie says, while also ensuring that the modified fungus doesn’t escape into nature. Even if logistical problems can be solved, it will be difficult to obtain regulatory approval to release a genetically modified plant pathogen fungus.
However, “the concept is worth exploring,” says Leslie. “Even if it fails, we should learn a lot about how to manage fungal populations.”
