Legume Genomics and Genetics 2024, Vol.15, No.1, 1-12 http://cropscipublisher.com/index.php/lgg 4 Figure 2 Source and distribution of carbon and energy in symbiotic nitrogen fixation (Adopted from Ke et al., 2022) 2.3 Interaction between nodule formation and nitrogenase system The process of root nodule formation is a series of ordered molecular events. Early studies have found that Nod factor can activate gene expression related to cell division and differentiation in the nucleus of plant roots, induce the inclusion and division of root hair cells, and form early nodule root structures. Through DNA microarray technology, it was found that NifA can directly control the expression of Nod genes and promote the secretion of Nod factors at this stage. The Nod factor regulates root fertilizer differentiation and growth through the recognition of plant adjacent membrane receptor complexes, obtaining more nutrient supply for root nodule development. The development process of rhizobia also regulates nitrogen fixation. By constructing different mutant strains of rhizobia, it was found that the ability of mutants lacking NifA related genes to form nodules was affected. This means that the nitrogen fixing gene promoter NifA can directly promote the expression of Nod gene and maintain the process of root nodule formation (Prithiviraj et al., 2003). Mature nodules have an appropriate structure that can provide a low oxygen atmosphere for rhizobia to isolate from the outside world. In addition, the abundant vacuoles in nodule cells can also provide abundant ammonia transport and storage space for nitrogen fixation. Research has found that under different oxygen concentration conditions, rhizobia can regulate NifA activity through an oxygen suffocation system, optimize nitrogenase levels and structures, and adapt to the needs of the root nodule microenvironment. This reveals the important role of root nodule morphology regulation in providing optimized conditions for nitrogen fixation. The above discusses the deep regulation of nitrogen fixation at different stages of nodule formation, as well as how the mature structure of nodules can in turn optimize the nitrogen fixation function of rhizobia, forming a complete interdependent regulatory network to jointly promote the efficient operation of both. It lays the foundation for in-depth research on this important symbiotic relationship mechanism. 3 The Relationship between Nitrogen Fixation and Growth and Development Regulation in Leguminous Plants 3.1 The impact of root nodule formation on plant growth and development The formation of root nodules in leguminous plants has a significant impact on their growth and development.
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