· Molecular Microbiology Research, 2025, Vol.15, No.1, 37-44 http://microbescipublisher.com/index.php/mmr 41 environments, GmSK2-8 does prevent GmNSP1 from binding to the NRE-box region in the symbiotic gene, resulting in a decrease in expression of these genes (Figure 2). This shows that this signal regulation mechanism is actually quite complicated. Figure 2 GmSK2-8 acts upstream of GmNSP1 and mediates salt-stress-inhibited nodule development (Adopted from He et al., 2020) 5.3.2 Expression regulation mechanisms of Rhizobium nitrogen fixation genes The nitrogen fixation gene of rhizobia is not always "on", but will be regulated by many factors. Taking Sinorhizobium fredii as an example, scientists discovered several key genes through metabolic modeling. These genes control the process of nitrogen fixation and provide new ideas for how we can regulate these genes and improve nitrogen fixation efficiency in the future (Contador et al., 2020). 5.3.3 Host plant regulation of Rhizobium symbiosis Soybeans themselves will also affect its "cooperative relationship" with rhizobia. Genetic studies have found that different soybean varieties have genetic differences in adapting to stress, which can affect nitrogen fixation effects (Wu and Yan, 2024). Researchers have also found many useful SNP markers from soybean’s nodule-related genes that can help us select soybean varieties that work better with rhizobia (Dwivedi et al., 2015). These results show that the genetic characteristics of soybeans also play an important role in this system. 6 Current Challenges and Existing Problems 6.1 Ecological adaptability issues in Rhizobium applications One of the biggest problems in improving the nitrogen fixation capacity of soybeans is whether rhizobia can adapt
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