Molecular Pathogens, 2025, Vol.16, No.5, 226-235 http://microbescipublisher.com/index.php/mp 226 Feature Review Open Access Improving Nitrogen Fixation in Soybean: Insights into Rhizobium Interactions Xinhua Zhou1, Zhonggang Li 2 1 Tropical Legume Research Center, Hainan Institute of Tropical Agricultural Resources, Sanya, 572025, Hainan, China 2 Tropical Specialty Crops Research Center, Hainan Institute of Tropical Agricultural Resources, Sanya, 572025, Hainan, China Corresponding author: zhonggang.li@hitar.org Molecular Pathogens, 2025, Vol.16, No.5 doi: 10.5376/mp.2025.16.0023 Received: 25 Aug., 2025 Accepted: 27 Sep., 2025 Published: 05 Oct., 2025 Copyright © 2025 Zhou and Li, This is an open access article published under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Preferred citation for this article: Zhou X.H., and Li Z.G., 2025, Improving nitrogen fixation in soybean: insights into rhizobium interactions, Molecular Pathogens, 16(5): 226-235 (doi: 10.5376/mp.2025.16.0023) Abstract As an important food crop, soybean has a huge demand for nitrogen. Symbiotic nitrogen fixation provides nitrogen to soybeans through rhizobia symbiosis, which is a key way to achieve sustainable agriculture and reduce the use of chemical fertilizers, and is of great significance for reducing environmental pollution. However, the current biological nitrogen fixation efficiency of soybean is not ideal and is restricted by factors such as strains, host plants, and environmental conditions. There is an urgent need to explore strategies to improve nitrogen fixation efficiency. This study systematically summarizes the research progress on improving the nitrogen fixation efficiency of soybean from the molecular mechanism of nodule formation, nitrogenase function and metabolic regulation, rhizobia recognition and signal transduction, host plant regulation, rhizobia genetic diversity, environmental factors, and molecular breeding and gene editing. By sorting out new insights into soybean-rhizobia interactions, we envision future directions for collaboratively optimizing host-microbe interactions and screening and improving efficient strains and varieties to enhance nitrogen fixation capabilities. Keywords Soybean; Rhizobia; Symbiotic nitrogen fixation; Gene editing; Rhizosphere microorganisms 1 Introduction Soybeans are widely grown in China, the United States, Brazil and other countries and are important grain and oil crops. Soybean grains are rich in protein and therefore have high nitrogen requirements. It is estimated that approximately 80 kilograms of nitrogen are needed to produce 1 ton of soybean grains (Freitas et al., 2022). Traditional agriculture uses a large amount of chemical nitrogen fertilizers to meet crop nitrogen needs, but excessive fertilization not only increases production costs, but also leads to environmental problems such as soil acidification and water eutrophication. In contrast, legumes form a symbiotic relationship with rhizobia to convert airborne nitrogen into a crop-available nitrogen source through biological nitrogen fixation (Nyzhnyk et al., 2024). This symbiotic nitrogen fixation system is one of the most efficient nitrogen fixation mechanisms in nature. It fixes a large amount of nitrogen for agricultural ecosystems every year and plays an important role in reducing dependence on chemical fertilizers. However, in actual production, the nitrogen obtained by soybeans through symbiotic nitrogen fixation is often difficult to fully meet high-yield needs. At present, the nitrogen fixation efficiency of soybeans is generally low, and it usually can only provide about half of the nitrogen needs of the plant, and the rest needs to be supplemented from the soil or chemical fertilizers. In areas lacking effective rhizobia, soybeans need to be inoculated with suitable strains, otherwise nodulation and nitrogen fixation levels will be low (Aliyat et al., 2018). In addition, adverse soil conditions such as drought, acid-base imbalance, and nutrient deficiency can inhibit root nodule formation and nitrogenase activity. These factors have resulted in the current underutilization of the potential of soybean symbiotic nitrogen fixation. In order to solve the above problems, improving the nitrogen fixation efficiency of soybean symbiosis has become a key issue. This requires in-depth study of the soybean-rhizobium interaction mechanism and the comprehensive use of a variety of technical means. In recent years, new progress has been made in research on root nodule development, signal transduction, host regulation, and strain improvement, providing new ideas for improving
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