Advanced genome-editing techniques have been used to create a strain of wheat resistant to a destructive fungal pathogen—called powdery mildew—that is a major bane to the world’s top food source, according to scientists at one of China’s leading centers for agricultural research.
To stop the mildew, researchers at the Chinese Academy of Sciences deleted genes that encode proteins that repress defenses against the mildew. The work promises to someday make wheat more resistant to the disease, which is typically controlled through the heavy use of fungicides. It also represents an important achievement in using genome editing tools to engineer food crops without inserting foreign genes—a flashpoint for opposition to genetically modified crops.
“This is very, very interesting; it is quite an accomplishment to knock out all three genes at the same time,” says Xing-Wang Deng, who heads a joint research center for plant molecular genetics and agricultural biotech at Peking University and Yale. “And this could be considered as a nontransgenic technology, so that can be very significant. I hope the government would not consider this transgenic, because the end result is no different than a natural mutation.”
There are currently no commercially planted varieties of genetically modified wheat anywhere in the world. And while many farmers are clamoring for access to such strains, genetically modified wheat remains highly controversial. Indeed, it’s not clear is whether Gao’s promising strain of wheat will make it out of the greenhouses in Beijing.
Gao says she has filed a global patent on the technology, suggesting it could be licensed. But there are no field trials planned yet.
Sequence-specific nucleases have been applied to engineer targeted modifications in polyploid genomes, but simultaneous modification of multiple homoeoalleles has not been reported. Here we use transcription activator–like effector nuclease (TALEN) and clustered, regularly interspaced, short palindromic repeats (CRISPR)-Cas9 technologies in hexaploid bread wheat to introduce targeted mutations in the three homoeoalleles that encode MILDEW-RESISTANCE LOCUS (MLO) proteins. Genetic redundancy has prevented evaluation of whether mutation of all three MLO alleles in bread wheat might confer resistance to powdery mildew, a trait not found in natural populations. We show that TALEN-induced mutation of all three TaMLO homoeologs in the same plant confers heritable broad-spectrum resistance to powdery mildew. We further use CRISPR-Cas9 technology to generate transgenic wheat plants that carry mutations in the TaMLO-A1 allele. We also demonstrate the feasibility of engineering targeted DNA insertion in bread wheat through nonhomologous end joining of the double-strand breaks caused by TALENs. Our findings provide a methodological framework to improve polyploid crops.
SOURCES – Technology Review, Nature Biotechnology