Field Crop 2024, Vol.7, No.2, 58-69 http://cropscipublisher.com/index.php/fc 59 This study summarizes the current knowledge on the genetic and molecular basis of symbiotic nitrogen fixation in legumes, including the identification and functional characterization of key genes involved in the process. Additionally, it discusses the agronomic benefits of incorporating legumes into cropping systems, focusing on their role in enhancing soil fertility, reducing the need for synthetic fertilizers, and promoting sustainable agricultural practices. This study also highlights recent advancements in the manipulation of nitrogen-fixing mechanisms and the potential for transferring these capabilities to non-legume crops to further improve agricultural productivity and sustainability. By addressing these objectives, this study seeks to underscore the importance of BNF in legumes and its potential to revolutionize agricultural practices, contributing to global food security and environmental sustainability. 2 Historical Background 2.1 Early discoveries in legume nitrogen fixation The phenomenon of nitrogen fixation in legumes has been recognized for over a century. Early studies identified the unique ability of legumes to enrich soil fertility through their symbiotic relationship with nitrogen-fixing bacteria, primarily rhizobia. This symbiosis was first observed in the late 19th century, leading to the understanding that legumes could convert atmospheric nitrogen into a form usable by plants, thus reducing the need for synthetic fertilizers (Kebede, 2021). 2.2 Evolution of research in symbiotic nitrogen fixation (SNF) Research into symbiotic nitrogen fixation (SNF) has evolved significantly over the past few decades. Since 1999, various genetic approaches have uncovered nearly 200 genes required for SNF in legumes. These discoveries have advanced our understanding of the evolution of SNF in plants and its relationship to other beneficial endosymbioses. Key areas of progress include signaling between plants and microbes, control of microbial infection of plant cells, nodule development, and the regulation of nodule senescence (Roy et al., 2020). Additionally, the integration of transcriptomic and metabolomic analyses has revealed that SNF enhances drought resistance in legumes, further highlighting the multifaceted benefits of this symbiotic relationship (López et al., 2023). 2.3 Milestones in BNF research Several milestones have marked the progress of biological nitrogen fixation (BNF) research. The development of dynamic vegetation models, such as LPJ-GUESS, has enabled the global quantification of nitrogen fixation rates and crop yields, providing valuable insights into the role of BNF in agricultural sustainability (Ma et al., 2022). Furthermore, the identification of a symbiotic flowering pathway in legumes has elucidated how fixed nitrogen and symbiotic signals promote reproductive success, thereby enhancing legume growth and production in nitrogen-poor soils (Figure 1) (Yun et al., 2023). The ongoing efforts to transfer nitrogen-fixing mechanisms from legumes to non-legumes, such as rice, maize, and wheat, represent a significant frontier in BNF research, with the potential to revolutionize agricultural practices and reduce dependency on synthetic fertilizers (Pankievicz et al., 2019; Mahmud et al., 2020). In summary, the historical background of nitrogen fixation in legumes encompasses early discoveries, the evolution of SNF research, and key milestones that have shaped our current understanding and application of this critical biological process. The integration of genetic, molecular, and ecological studies continues to drive advancements in this field, promising sustainable agricultural solutions for the future. 3 Genetic Mechanisms of Nitrogen Fixation 3.1 Key genes involved in SNF Symbiotic nitrogen fixation (SNF) in legumes is a complex process that involves numerous genes. Research has identified nearly 200 genes essential for SNF in model legumes such as Medicago truncatula and Lotus japonicus, as well as in crop species like soybean (Glycine max) and common bean (Phaseolus vulgaris) (Roy et al., 2020). These genes are involved in various stages of the symbiotic process, including signaling between plants and microbes, microbial infection of plant cells, nodule development, and the control of bacteroid differentiation and nodule senescence. Key genes such as those encoding for nodulation factors and receptors, transcription factors, and transporters play crucial roles in these processes (Roy et al., 2020).
RkJQdWJsaXNoZXIy MjQ4ODY0NQ==