Molecular Microbiology Research 2024, Vol.14, No.2, 109-118 http://microbescipublisher.com/index.php/mmr 112 Figure 1 Summarized model for symbiotic nitrogen fixation in legumes by rhizobia (Adopted from Lindström and Mousavi, 2019) Image caption: The figure illustrates how rhizobia interact with the roots of leguminous plants to form nodules and carry out nitrogen fixation. Rhizobia fix atmospheric nitrogen and convert it into ammonia, which plants can utilize, thereby enhancing plant growth and improving soil fertility (Adapted from Lindström and Mousavi, 2019) 3.3 Molecular signaling between rhizobia and legumes The symbiotic relationship between rhizobia and legumes is orchestrated by a complex network of molecular signals. The initial recognition involves the exchange of flavonoids and Nod factors, which activate downstream signaling pathways in both the plant and the bacteria. In legumes, microRNAs such as miR2111 play a crucial role in maintaining the susceptibility of roots to rhizobial infection by regulating key suppressors of symbiosis (Tsikou et al., 2018). Additionally, systemic signaling mechanisms, including the allocation of sucrose and the oxidative pentose phosphate pathway, adjust nodule formation and function based on the plant's nutritional status (Lepetit and Brouquisse, 2023). Transcription factors also integrate environmental signals with symbiotic signaling to modulate nodule development and function (Chakraborty et al., 2022). 4 Role of Rhizobia in Enhancing Legume Growth 4.1 Nutrient uptake and utilization Rhizobia play a crucial role in enhancing nitrogen uptake in legumes through the process of symbiotic nitrogen fixation. This process involves the conversion of atmospheric nitrogen (N2) into ammonia (NH3), which is then assimilated into amino acids by the plant. Studies have shown that inoculation with effective rhizobium strains significantly increases nitrogen fixation and uptake in legumes. For instance, Vicia faba inoculated with strains NSFBR-12 and NSFBR-15 fixed 87.7% and 85.5% of the total nitrogen uptake, respectively, demonstrating the substantial contribution of rhizobia to nitrogen nutrition in legumes (Allito et al., 2020). Additionally, the effectiveness of nitrogen fixation in rhizobia has been a focal point of research, aiming to improve the efficiency of this process for sustainable food production (Lindström and Mousavi, 2019). Rhizobia not only enhance nitrogen uptake but also improve the utilization of other essential nutrients such as phosphorus and potassium. The presence of rhizobia can lead to better phosphorus uptake, as observed in Vicia faba, where soil available phosphorus and pH significantly influenced phosphorus uptake in inoculated plants (Allito et al., 2020). Moreover, rhizobia can solubilize precipitated phosphorus, making it more available to the plant, and produce siderophores that help in the uptake of iron, which is crucial for various plant metabolic processes (Fahde et al., 2023).
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