Legume Genomics and Genetics 2025, Vol.16, No.2, 81-90 http://cropscipublisher.com/index.php/lgg 82 well as the genetic regulatory mechanisms behind root tumor development. This study hopes to find some new directions for enhancing the nitrogen fixation capacity of soybeans through these reviews and also provide some references for the future green transformation of agriculture. 2 Molecular Basis of Soybean-Rhizobium Symbiosis 2.1 Role of Nod factors and their perception by soybean root cells To start symbiosis, soybeans and rhizobia need to greet each other first, and the "tumor-forming factor" is precisely the first signal sent by rhizobia. These lipid shell oligosaccharide structure signal molecules can be "heard" by the NFR1 and NFR5 receptors on soybean root hairs. Once identified successfully, these two recipients will team up to form a complex and transmit the signal in. During this process, guanine nucleotide exchange factors such as GmGEF2 are phosphorylated, small GTPases (such as GmROP9) become active, and scaffold proteins such as GmRACK1 are added. Finally, a multi-protein complex specifically for processing symbiotic signals is formed (Figure 1) (Gao et al., 2021; Yuan et al., 2023). Of course, not all plants can "communicate" like this. The matching degree between signal molecules and receptors determines whether this relationship can hold and how efficient it is (Kidaj et al., 2020; Kronauer and Radutoiu, 2021). 2.2 Early signaling events in nodule formation After perceiving the Nod factor, the root's response is also very fast. First, there is a fluctuation in membrane potential, followed by a rapid increase in calcium ion concentration, and receptor-like kinases and G protein signaling pathways are also successively awakened. Take NFR1 as an example. It interacts with RGS proteins and causes them to phosphorylate, thereby regulating G protein activity - which is crucial in controlling root tumor formation (Choudhury and Pandey, 2024). Meanwhile, early response genes, such as ENOD40, as well as transcription factors like NIN and NSP1, also began to be upregulated, promoting root hair deformation, infection filament entry, and cortical cell division (Singh et al., 2021). However, things do not progress so linearly - the REDOX state and hormone signals within plants, such as the interweaving of auxin and cytokinin, can also interfere with or regulate these early steps, ensuring that root nodules grow where and at the right time (Buhian and Bensmihen, 2018). 2.3 Cellular reprogramming in response to symbiotic cues The behavior of cells undergoes a series of changes under the influence of signals. For instance, the structure of the root cytoskeleton will be rearranged, transcription factors such as WRKY17 that are specifically active in root nodules will be activated, and micrornas (like miR172c, miR167) will also begin to participate in regulating those important genes related to nodules (Wang et al., 2014; Wang et al., 2015). This reprogramming is not limited to the surface - the root hairs will deform, the infected filaments will drill in all the way, and the cortical cells will start to divide, eventually forming the root nodule primordia. Subsequently, complex processes such as the formation of symbiotic membranes and cell functional differentiation unfolded one after another, establishing channels for nutrient and signal exchange between plants and bacteria (Geurts et al., 2005). However, this process is not entirely autonomous - it is simultaneously regulated by local signals, whole-plant feedback, and even the external environment. For instance, the plant's own "nodule regulation circuit" sometimes presses the pause button to control the number and distribution of root nodules (Fernandez-Gobel et al., 2019). 3 Key Classes of Signaling Genes Involved in Soybean-Rhizobium Interaction 3.1 LysM receptor-like kinases (e.g., GmNFR1, GmNFR5) and their recognition roles Whether soybeans can "understand" the signals of rhizobia depends on a type of protein called LysM receptor-like kinases, especially GmNFR1 and GmNFR5. From the very beginning, it was they who were responsible for identifying the nodular factors released by rhizobia. However, this recognition is not merely a single dialogue; it is more like a "linkage" involving multiple parties - these receptors will form complexes together with other proteins such as GmREM1a and may also be regulated by the rhizobia effector factor NopL, which can enhance the recruitment ability of GmNFR5, thereby promoting the amplification of symbiotic signals. The expression level of
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