Researchers at the University of California, Davis, have found a way to reduce the amount of nitrogen fertilizer needed to grow cereal crops. Using CRISPR-based gene editing, the researchers found a new pathway for cereal crops to capture nitrogen-aka nitrogen fixation-as they grow. The discovery could save farmers in the US billions of dollars annually in fertilizer costs while also reducing nitrogen pollution.
Nitrogen fixation is a sort of miracle feature of plants in the “Fabaceae” family, commonly known as the legume, pea, or bean family. The group contains a wildly diverse array of trees, shrubs, and perennial plants, including key crops like soybeans, chickpeas, alfalfa, and peanuts. The great majority of legumes contain a symbiotic bacteria called Rhizobia within nodules in their root systems. These bacteria extract nitrogen from the air and convert or “fix” it into ammonium that feeds the plant.
Nitrogen is the most commonly deficient nutrient in many soils around the world and it is the most commonly supplied plant nutrient. Cereal plants like rice and wheat don’t have the ability to fix nitrogen and must rely on taking in inorganic nitrogen, such as ammonia and nitrate, from chemical fertilizers. Scientists have tried to induce the nitrogen-fixation process in crops but this new research appears to be the first success so far.
Without getting too technical, one of the key traits of legumes is the root nodules. Their symbiotic bacteria are free living in the soil until they are able to sense flavonoids, which are secreted by the roots of their host plant. This triggers the accumulation of a large population of Rhizobia and eventually attachment the root cells, where they proliferate and form the root nodule.
Inside the nodule, the bacteria fix atmospheric nitrogen into ammonium, using the enzyme nitrogenase. In return, the plant supplies the bacteria with carbohydrates. Most importantly, the nodules provide an oxygen starved environment for the bacteria, which is essential to fix nitrogen.
The UC Davis researchers, led by Eduardo Blumwald, a distinguished professor of plant sciences, used chemical screening and genomics to identify compounds in rice plants that enhanced the nitrogen-fixing activity of the bacteria. Then they identified the pathways generating the chemicals and used gene editing technology to increase the production of compounds that stimulated the formation of biofilms. These biofilms, in turn, form a barrier against oxygen and allow the nitrogen-fixing bacteria to accumulate and thrive.
The plants were grown in nitrogen-deficient soils that reduced yields for conventional as well as gene-edited rice plants. However, the rice plants that incorporated Blumwald’s new gene-edited trait had yield’s up to +40% higher than those without the trait.
Blumwald says the technique will work for almost any crop. In fact, they’ve already created wheat plants with the trait, though they’ve not completed tests. A patent application has also been filed by the University of California and is pending. Blumwald believes the trait can be widely incorporated into commercial crops within the next five to ten years, creating substantial savings for farmers and reducing damage caused by chemical nitrogen leaching into soils and groundwater. The study, published in the journal Plant Biotechnology, is available HERE.
