PULLMAN – Researchers at Washington State University and in the United Kingdom have announced a discovery that may someday allow the world’s farmers to decrease their dependence on nitrogen fertilizers, resulting in billions in savings to farmers and a reduction in the amount of nitrogen pollution that has already turned some waterways into dead zones.
Legumes, such as beans, peas, and alfalfa, host billions of bacteria in tiny nodules along their roots. The bacteria convert, or “fix,” atmospheric nitrogen into a form the plants can use. But in findings reported in the June 29 issue of the journal Nature, researchers from WSU and the John Innes Centre, U.K., report they have discovered a way to make plants produce spontaneous nodules without the bacteria.
Non-leguminous crops such as wheat and corn, don’t form nodules or cultivate relationships with nitrogen-fixing microbes. They must be treated with nitrogen-rich fertilizers in order to grow and produce at peak levels.
But WSU lead investigator B.W. (Joe) Poovaiah said their work raises the possibility of someday producing non-leguminous plants that can form symbiotic relationships with nitrogen-fixing bacteria just as legumes do.
“If major field crops such as wheat and corn can fix nitrogen from the atmosphere, it will help with two problems,” Poovaiah said. “You’re going to help the farmers, and help Mother Nature.”
Researchers Poovaiah, Shubho Chaudhuri and Tianbao Yang at WSU, and colleagues from the John Innes Centre in the United Kingdom, worked on a gene that plays a key role in nodule formation in legumes. Most non-leguminous plants also have the gene, called CCaMK (pronounced “see-kam-kay”). Poovaiah said the CCaMK gene, which his team first cloned in 1995, codes for a protein that influences many activities within the plant. His group’s work on the gene over the past decade laid the groundwork for the new findings.
In the current study, Poovaiah’s team found that in biochemical tests, CCaMK from lily performs much like its counterpart in Medicago truncatula, a relative of alfalfa, even though lily cannot fix nitrogen. They then determined whether the lily gene could function the same way in a real-life situation by removing the gene from Medicago and replacing it with the lily gene. They found that the replacement gene substituted for the missing one. When grown in the presence of nitrogen-fixing bacteria, the experimental plants developed nodules on their roots just like the nodules seen on normal plants.
The researchers did a further experiment in which they removed parts of the CCaMK gene before inserting it into Medicago. When a certain region of the gene was deleted, the Medicago roots made nodules even if no bacteria were present. They did not, however, fix nitrogen; bacteria were still needed to do that. This result indicates that the segment of the CCaMK gene that was removed normally inhibits nodule formation. Poovaiah said in a normal legume, bacteria send a chemical signal that tells the root cells to allow CCaMK to become active so that nodules can form.
He said it’s still a mystery why lilies and other non-legumes don’t make nodules or host nitrogen-fixing bacteria. Since they have a normal CCaMK gene, they are probably missing some other part of the pathway that leads to a legume-type symbiosis.
Poovaiah said understanding the rest of the pathway could lead to the conversion of non-nodule-forming plants into plants that are able to host nitrogen-fixing bacteria, reducing the amount of fertilizer used. That would be a tremendous boon to farmers, for whom nitrogen fertilizers are a major expense. Such fertilizers are a petroleum by-product, so their price has skyrocketed along with the price of crude oil.
There are also huge environmental costs to using nitrogen fertilizers. Nitrogen leaches from farm fields into groundwater and streams, at times reaching high enough levels to kill nearly everything in the water. According to The Nature Conservancy, thousands of square miles of the Gulf of Mexico are now a “dead zone” due to the 1.5 million metric tons of nitrogen fertilizer that are washed from mid-American farms into the Mississippi River every year.
While more work is needed before farm-ready applications of his work are available, Poovaiah is optimistic that it could happen within the next decade.
“We’re a research university,” Poovaiah said. “Our job is to open new doors, and this we have done.”
Poovaiah is a professor in WSU’s Department of Horticulture and the Center for Integrated Biotechnology.
Related articles about Poovaiah and his research can be found at :
* Nature journal, June 29, 2006,
* Scienceagogo.com, http://www.scienceagogo.com/news/20060528231843data_trunc_sys.shtml
* WSU news service, http://researchnews.wsu.edu/health/86.html
* Washington State Magazine, http://washington-state-magazine.wsu.edu/stories/2006/May/NoShrinkingViolet.html.