Legume Genomics and Genetics 2024, Vol.15, No.1, 1-12 http://cropscipublisher.com/index.php/lgg 2 In recent decades, significant progress has been made in the research of leguminous plants in various aspects such as nitrogen fixation, growth and development regulation, and gene expression regulation. The in-depth study of the symbiotic relationship between rhizobia and plants has revealed the molecular mechanism of nodule formation and its role in nitrogen fixation. The application of molecular biology, genetics, and biochemistry methods has enabled us to better understand nitrogen fixation signaling pathways and the key molecules involved. At the same time, the technological development of genomics and transcriptomics provides powerful tools for the analysis of gene regulatory networks in leguminous plants. The research process of leguminous plants has witnessed human attention and efforts towards agricultural production and ecological environment. From ancient times to the present, significant achievements have been made in the study of nitrogen fixation mechanisms and growth and development regulation. With the promotion of new technologies and interdisciplinary cooperation, the future prospects of leguminous plant research are still broad, which will further promote the sustainable development of agriculture and the healthy maintenance of ecosystems. 2 The Mechanism of Nitrogen Fixation in Leguminous Plants 2.1 Root nodule development mechanism The symbiotic nitrogen fixation between leguminous plants and rhizobia is an efficient biological nitrogen fixation system and the most important green nitrogen source in natural soil. Analyzing the molecular regulatory mechanism of symbiotic nitrogen fixation between leguminous plants and rhizobia is not only of great scientific significance, but also an important guarantee for human beings to achieve sustainable agricultural development. Therefore, this research field has been one of the hot topics in plant biology for many years. The research team of Wang Ertao, a researcher at the Center for Excellence and Innovation in Molecular Plant Science of the Chinese Academy of Sciences, has made breakthrough research progress in this field, and discovered the molecular mechanism of SHR-SCR molecular regulation module regulating the initiation of root nodules of leguminous plants by determining the fate of cortical cells (Zhuang et al., 2021). The cortex of the roots of leguminous plants undergoes rapid cell division and proliferation after invasion by rhizobia, leading to the formation of nodules. However, the cortex of non leguminous plants cannot respond to the invasion of rhizobia to produce nodules. Their research found that unlike the expression patterns of key genes SCR (SCARECROW, endothelial layer specific expression) and SHR (SHORTROOT, column specific expression) that regulate Arabidopsis root development, the homologous genes MtSHR and MtSCR in alfalfa appear in the root cortex. Further analysis revealed that the regular arrangement of key regulatory elements AT-1 box and enhancer sequences in the promoter region of MtSCR is conserved in leguminous plants, but there are significant differences in non leguminous plants. Genetic analysis shows that the expression of MtSCR and MtSHR in the cortex is extremely important for the occurrence of root nodules, and their mutant root nodule production ability is significantly reduced. Cytokinin has been shown to regulate the symbiotic relationship between plants and rhizobia, the division of cortical cells, and the initiation of root nodules. However, this promoting effect of cytokinin is significantly reduced in Mtscr-1 and MtSHR1-SRDX (simulating SHR mutants by inhibiting the transcriptional activity of SHR), once again confirming the core role of MtSHR and MtSCR in root nodule initiation (Dong et al., 2021). SHR-SCR is a key module in the stem cell program of plant development, expressed in the stem cell region and endothelial layer of plants. This study found that during the evolution of leguminous plants, the key stem cell gene SCR in leguminous plants is expressed in cortical cells, and another key stem cell transcription factor SHR moves to cortical cells after vascular bundle expression. As a result, the cortical cells of leguminous plants obtain the SHR-SCR stem cell submodule. This stem cell molecular module endows the cortex cells of leguminous plants with the ability to divide, making the cortex of leguminous plants different from non leguminous plants. At the same time, the stem cell molecular module can be activated by signals from rhizobia, inducing cortical division and forming nodules in leguminous plants such as alfalfa (Figure 1) (Dong et al., 2021).
RkJQdWJsaXNoZXIy MjQ4ODYzNA==