Helping wheat defend itself against damaging viruses
Wheat diseases caused by a host of viruses that might include wheat streak mosaic, triticum mosaic, soil-borne mosaic and barley yellow dwarf could cost producers 5 to 10 percent or more in yield reductions per crop, but a major advance in developing broad disease-resistant wheat is on the horizon.
John Fellers, molecular biologist for the U.S. Department of Agriculture’s Agricultural Research Service, and Harold Trick, plant geneticist for Kansas State University, have led an effort to develop a patent-pending genetic engineering technology that builds resistance to certain viruses in the wheat plant itself. And although genetically engineered wheat is not an option in the market today, their research is building this resistance in non-genetically engineered wheat lines as well.
“(Wheat viruses) are a serious problem,” Trick said. “Wheat streak mosaic virus is one of the most devastating viruses we have. It’s prevalent this year. In addition to that, we have several other diseases, triticum mosaic virus and soil-borne mosaic virus, that are serious diseases.”
Knowing how costly these diseases can be for producers, Fellers has worked on finding solutions for resistance throughout his career. As a doctoral student at the University of Kentucky, he used a technology in his research called pathogen-derived resistance, or RNA-mediated resistance — a process that requires putting a piece of a virus into a plant to make it resistant to that particular virus. Most of the viruses that infect wheat are RNA viruses, he said.
“The plant has its own biological defense system,” Fellers said. “We were just triggering that with this technology.”
Now Fellers, with the help of Trick, his wheat transformation facility and K-State graduate students, have developed transgenic wheat lines that contain small pieces of wheat streak mosaic virus and triticum mosaic virus RNA.
“It’s kind of like forming a hairpin of RNA,” Fellers said. “What happens is the plant recognizes this RNA isn’t right, so it clips a piece of it and chops it up, but then it keeps a copy for itself. Then we have a resistance element.”
Fellers compared the process to the old days of viewing most wanted posters on the post office wall. The piece of foreign RNA from the virus, which is a parasite, is one of those most wanted posters. Because the virus is a parasite, it has to seize or hijack part of the plant system to make proteins that it needs to replicate.
When the virus comes into the plant, the plant holds up that poster from the post office wall, recognizes the virus, and doesn’t allow the virus to replicate and go through its lifecycle.
A broad resistance goal
Trick said it wasn’t difficult to incorporate the RNA into the wheat, as it involved a standard transformation process where the DNA encoding the RNA was introduced into plant cells, plants were regenerated from these transformed cells, and then the transgenic plants underwent testing for disease resistance.
“The problem with this technology is the most wanted poster is only for one individual,” Trick added. “If we were trying to target multiple genes, we’d have to make another vector for a second virus, then create that transgenic, which we have done. So, we have different plants that are genetically resistant to wheat streak mosaic virus and plants that are resistant to triticum mosaic virus. We would like to get something that has broad resistance to many different viruses.”
Knowing again that the viruses are parasites that rely on part of the plant system to replicate, it may be possible to shut off these plant systems to prevent viral replication, Trick said, which in essence means making a most wanted poster for specific plant genes.
Fellers and Trick have made additional transgenic plants with a most wanted poster for these plant genes and tested their new plants for resistance to a number of wheat viruses.
“We’re now able to target barley yellow dwarf and soil-borne mosaic viruses,” Fellers said. “We’ve also done mixed infection tests with wheat streak mosaic and triticum mosaic (viruses), and our initial results now are that they’re all resistant. We’re very cautious, but our initial indications show we have come up with something that provides broad resistance to these four viruses. We thought it was important enough to file for a patent.”
Fellers said this work is a proof of concept, meaning it shows that researchers have an ability now to address these virus issues. The fact that the process uses genetic engineering would mean that getting broad-resistance wheat would take some time considering the public and industry would have to accept it first.
However, Trick said they are now pursuing a non-genetically engineered method that involves turning off specific plant genes using mutations. With this method, the researchers could develop the technology and incorporate it into the K-State breeding program without regulations.
“We would hope the turn around time would be quick, but it’s still classical breeding,” Fellers said of using mutations. “It’s a matter of developing markers and getting them in the varieties. We have been using Jagger and Karl 92, varieties that are already past their prime, so we have to get them in some newer varieties.”
Source: Kansas State University Research and Extension. www.k-state.edu