Gene editing techniques recover benefits lost in domestication
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Reinstating genes lost during domestication can make crops tougher and provides an alternative to using foreign genes to modify plants, Danish researchers say. New techniques that tinker with DNA, swapping in genes from undomesticated relatives, can make crops more similar to their original wild versions.
“Wild plants tend to manage much better under harsh conditions than their cultivated relatives,” says Michael Palmgren, a plant biologist at the University of Copenhagen. “Many important properties of wild plants were unintentionally lost during thousands of years of breeding.”
The new techniques could restore some of the properties lost in domesticated crops, Palmgren and colleagues contend in a review article published online December 16 in Trends in Plant Science. “We estimate that all crops would benefit from rewilding,” he says. Crops could be modified to draw nutrients from the soil more efficiently and be made more resilient against drought, cold, diseases and pests.
Such an approach, called reverse breeding, is not a new concept, says Mark Sorrells, a plant breeder and geneticist at Cornell University. “What they’re calling ‘back to nature’ practices are practices that have been used by farmers in varying degrees for many years,” he says.
“It is true that in the process of domestication and breeding modern varieties, genetic variation for some characteristics has been lost, and that is why breeders routinely go back to wild relatives to find that genetic variation.”
And the challenge that Palmgren and coauthors raise — identifying mutations found in domesticated crops but not in their wild cousins — is not the biggest technical hurdle, Sorrells says. “Once you find these traits, mapping them and transferring them to modern varieties is what is the formidable task.”
By 2050, the world’s population is predicted to surpass 9 billion. One strategy to meet food demands is to give crops new genes with benefits their wild relatives never had. These transgenic crops, also known as genetically modified organisms, are viewed with distrust by many people.
Traditionally, reverse breeding has been carried out by crossing crops with wild versions of the plant that have the desired trait. But the resulting hybrid may also end up with other qualities that breeders had intentionally gotten rid of. “Wild plants are seldom tasty, nutritious, and easy to harvest,” says Palmgren. The process of perfecting the hybrid plant is time-consuming and difficult to control.
Today’s biotechnology can surgically repair the deficiencies in crops, says Palmgren. One method, called cisgenesis, inserts a gene from a wild relative into a crop. In May, researchers from Korea and the Netherlands reported using cisgenesis to transfer genes from wild potatoes into domesticated relatives, making the crops more resilient to blight from the fungus Phytophthora infestans.
Researchers in Switzerland and Germany have also used cisgenesis to insert a single gene into Gala apples to make them less vulnerable to apple scab, a condition caused by the fungus Venturia inaequalis. To make the apple as hardy as its wild cousins, however, will require the addition of multiple genes.
With cisgenesis, “you don’t need to go through extensive crossing to induce the trait, so it basically makes the whole process faster,” says Vladimir Nekrasov, a plant biologist at the Sainsbury Laboratory in Norwich, England.
Another method, precision mutagenesis, is even more exacting. Researchers change the order of DNA building blocks to return a gene to its wild form. So far the method has been tested on several plants, including tobacco, sorghum and rice.
Palmgren and coauthors discuss only techniques that edit one or a few genes and are not effective for improving traits controlled by many genes, says Sorrells. Another technique, genomic selection, allows researchers to survey a sample of genetic variants in a crop’s genome to predict which variations are most likely to result in higher yields or resilience against disease. Genomic selection allows researchers to pick out individuals that have more of the genes that contribute to the trait in question.
“These authors didn’t even mention that, and it’s probably one of the most exciting technologies currently being researched in plant breeding,” Sorrells notes.
Clay Sneller, a plant breeder and geneticist at Ohio State University in Columbus, also expressed skepticism. “I find their whole premise to be rather flawed,” he said. “They appear to think that during breeding we have accumulated negative mutations, and if we got rid of those mutations then the crop would be better. They reviewed no evidence that this occurs on a wide scale in genes that truly matter.”
M.G. Palmgren et al. Are we ready for back-to-nature crop breeding? Trends in Plant Science. Published online December 16, 2014. doi: 10.1016/j.tplants.2014.11.003.
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S. Milius. Borrowed genes raise hope for fixing “slow and confused” plant enzyme. Science News Online, September 19, 2014.