· Molecular Microbiology Research, 2025, Vol.15, No.1, 37-44 http://microbescipublisher.com/index.php/mmr 38 encountering a stress environment like salt, GmSK2-8 will "deal" with some key transcription factors, such as GmNSP1a and GmNSP1b, making them unable to work properly. These transcription factors were originally used to help rhizobia infect soybean roots and make the rhizoblasts grow. But GmSK2-8 will add phosphoric acid to them (this process is called phosphorylation), making them "weak", which will affect their ability to bind to the gene promoter. In this way, nodules are not easily formed in salty environments (He et al., 2020). 2.2 Key genes in the symbiotic nitrogen fixation process In the process of nitrogen fixation, several particularly important genes play a major role. A small heat shock protein called GmHSP17.9 will increase when the nodule grows. It regulates nitrogen fixation and final yield, and can also help another protein called GmNOD100 (actually a sucrose synthase) work together to make nodules develop more smoothly. If the amount of GmHSP17.9 changes, it will affect the number of nodules, the activity of nitrogenase, and even affect the growth of the entire soybean plant (Yang et al., 2021). In addition, there is a phosphorus transporter called GmPT7, which can transport phosphorus elements into nodules. This is also important for the function of nodules and soybean yield (Chen et al., 2018). 2.3 Environmental factors influencing soybean-Rhizobium interactions The partnership between soybeans and Rhizobium can be affected by the environment. For example, salt and nitrogen are two common influencing factors. Salt stress increases the expression of GmSK2-8, thereby suppressing the expression of some important symbiotic genes and affecting the formation of nodules. Another problem is nitrates in the soil. Too much nitrate will make the nodules difficult to grow and will also hinder the nitrogen fixation process. But the good news is that some special rhizobia strains can still form effective nodules and fix nitrogen even in soils with a lot of nitrates (Nguyen et al., 2019). In addition, studies have found that small gases such as hydrogen sulfide (H₂S) are also helpful. It can improve the ability of soybeans to absorb and utilize nitrogen, and can also help plants grow better and produce higher yields when they are lacking (Zhang et al., 2020). 3 Rhizobium Diversity and Nitrogen Fixation Efficiency in Soybean 3.1 Ecological diversity of Rhizobium 3.1.1 Geographical distribution and ecological adaptation of Rhizobium There are many types of rhizobia, and they can survive in different places and under different conditions. For example, Sinorhizobium fredii can "cooperate" with soybeans in the saline-alkali land of China's Huanghuai Plain to successfully form nodules. This shows that it is very adaptable to this particular soil (Contador et al., 2020). In addition, some rhizobia can still help soybeans fix nitrogen in a high nitrate environment, indicating that they can adapt to many types of farmland (Wang et al., 2024). 3.1.2 Symbiotic effects and community dynamics of Rhizobium The relationship between rhizobia and soybeans will actually be affected by other microorganisms. For example, if there are bacteria like Azospirillum near the roots, they may change the number of rhizobia and even affect the effect of nitrogen fixation (Bender et al., 2022). Different planting methods, such as the use of intercropping (sourcing two crops together), will also affect the diversity of root bacteria, and thus affect the nitrogen fixation capacity (Cheng et al., 2023). 3.1.3 Influence of soil microbial communities on Rhizobium diversity Other microorganisms in the soil, such as Bacillus, can sometimes affect the role of rhizobia. They may change the relationship between bacterial flora and also affect the expression of some nitrogen-related genes, which will result in a decrease in nitrogen fixation efficiency (Wang et al., 2024). In addition, the nitrogen content, pH (pH value) and so on in the soil will also affect the type and number of Rhizobium. For example, the abundance of some Bradyrhizobium is related to these factors. 3.2 Genomic characteristics of Rhizobium and their relationship to nitrogen fixation efficiency What "rthroblast genes look like" has a lot to do with whether it can help soybeans fix nitrogen better. For
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