Legume Genomics and Genetics 2025, Vol.16, No.2, 81-90 http://cropscipublisher.com/index.php/lgg 87 What's more interesting is that GmNARK not only manages root nodules, but also plays a role in coping with stresses such as salinization and drought. It can also interact with other signaling pathways (Cheng et al., 2018). So, from the perspective of regulation, it is more like a dispatching center rather than a simple switch. 7 Biotechnological Applications and Breeding Implications in Soybean-Rhizobium Interaction 7.1 Identification of gene targets for enhancing nitrogen fixation Some genes related to nitrogen fixation were not so easy to discover from the very beginning. It was not until the development of quantitative trait loci (QTL) mapping and transcriptomics research that researchers gradually identified the positions of some of these "hidden heroes". For example, on chromosome 18, a QTL that is different from the known Rj/rj nodular gene was found. It contains a nucleotide-binding gene with leucine repeats, and the expression varies significantly among different varieties (Teraishi et al., 2025). This discovery offers us a new direction: perhaps in a low-nitrogen environment, such genes can help soybeans enhance symbiotic efficiency. In addition, there are some classic symbiotic genes that have long been noticed, such as Nif, nodA, IAA, exoX, htrA, etc., which are involved in flavonoid synthesis, signal sensing, and resilience mechanisms. They can all be found in the symbionts of soybeans and rhizobia, especially when facing environmental stress. Their existence is even more significant (Ni et al., 2024). 7.2 Development of soybean lines with optimized nodulation signaling In field experiments, sometimes the true capabilities of genes can be better revealed than in laboratories. The breeding team is now attempting to use natural variations and recombinant inbred lines to screen for soybean varieties that are more active in nodulation and have stronger nitrogen fixation capabilities. Moreover, when used in combination with good rhizobia strains, the performance of such varieties is usually more stable and the yield increase is more significant (Kolapo et al., 2025). Some regions have even improved farmers' income in this way. Of course, relying solely on the inoculation of a single strain may not necessarily cover the complex field environment. Thus, the strategy of using rhizobia together with other beneficial microorganisms, such as mycorrhizal fungi, also began to gain popularity. This "microbial mix" not only enhances nutrient absorption rate but also shows potential in improving stress resistance (Wangiyana et al., 2022). 7.3 Potential for gene editing and synthetic biology approaches in legume improvement Traditional breeding relied on time and screening, but now there are some more "shortcut" methods. For instance, the CRISPR-Cas gene editing technology can directly "cut" on the target gene, bypassing the complex selection process in the middle. Verifying the functions of candidate genes through this approach is not only highly efficient but also accelerates the screening of strains that are more favorable for symbiosis, stress resistance, and strain compatibility (Ni et al., 2024). On the other hand, the development of synthetic biology has also opened up new paths. Some people have begun to attempt to "modify" the rhizosphere microbiome, and even design artificial microbial communities that are suitable for specific soybean varieties. This strategy, starting from the root ecosystem, aims to enhance nitrogen fixation capacity and optimize growth conditions, thereby driving an overall increase in yield. 8 Concluding Remarks Regarding the interaction between soybeans and rhizobia, no one simply regards it as a matter of "who infects whom" anymore. This is a complex molecular exchange involving many signaling genes and regulatory pathways. It is not merely about controlling nodules and nitrogen fixation, but also related to plants' responses to various environmental changes. In this regard, host genes such as NFRs, NSPs, NIN and Rj2/Rfg1 are research hotspots. On the microbial side, many effector molecules have also been proven to be directly related to compatibility, defense response and symbiotic efficiency. However, these effects are not universal. The rhizosphere environment, plant genotypes, and even seasonal changes can all influence the symbiotic effect. Especially the mutually beneficial relationship between rhizobia and mycorrhizal fungi, combined with the cooperation of other beneficial microorganisms, can truly bring about practical benefits such as nutrient absorption, enhanced resistance, and increased yield.
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