An international study identifies new mechanisms core topic for biological nitrogen fixation in plants

An international team, including José María García-Mina and Ángel Zamarreño, researchers at the BIOMA Institute of the University of Navarra, has identified new molecular mechanisms that allow legumes to utilize atmospheric nitrogen through their association with beneficial soil bacteria. The findings, published in the scientific journal *New Phytologist*, contribute to a better understanding of biological nitrogen fixation, which plays a fundamental role in soil fertility and helps reduce dependence on industrial nitrogen fertilizers, whose production and use have significant environmental impacts.

Nitrogen makes up approximately 78% of the atmosphere. However, most plant species cannot use it directly. Legumes, such as peas, beans, and alfalfa, have an advantage: they can form a symbiotic relationship with certain soil bacteria, known as rhizobia, that are capable of converting atmospheric nitrogen into compounds the plant can use. This association takes place in small Structures that form on the roots, called nodules.

The researchers sought to unravel the mechanism by which bacteria and plant cells exchange nutrients and how the nitrogen obtained is distributed to the rest of the plant. To do so, they studied a family of transporter proteins called UMAMIT, which is involved in the movement of amino acids across cell membranes. Using the species Medicago truncatula, they identified several genes whose activity increases during the establishment and development of the symbiosis.

Using Genetics nd CRISPR-Cas9 editing techniques, they simultaneously inactivated three genes in this family. The results showed that, although the modified plants continued to form nodules, their ability to fix nitrogen decreased significantly. “We observed reductions of up to 41% in nitrogenase activity and up to 82% in plant biomass, accompanied by symptoms of nitrogen deficiency and lower concentrations of essential amino acids required for their transport,” says José María García-Mina.

In addition, they found that one of the proteins, MtUMAMIT17, is localized in cellular Structures s involved in the exchange of nutrients between the bacteria and the plant. These findings demonstrate that nodule training alone does not guarantee efficient nitrogen fixation; specific nutrient transport mechanisms are also necessary.

Although the authors emphasize the need for further research in this area, the study highlights that understanding the mechanisms that regulate this process can contribute to the development of strategies that improve crops’ natural use of nitrogen, thereby promoting more efficient and sustainable agricultural systems.

· Bibliographicreference letter : Winning, C. S. et al. (2026). Symbiosis-associated UMAMIT transporters required for establishing efficient nitrogen fixation in Medicago truncatula. New Phytologist, 250, 530–546. https://doi.org/10.1111/nph.70917