Nodules are unique organs formed on the roots of leguminous plants through a symbiosis with rhizobia bacteria. Nodules enable symbiotic nitrogen fixation, which plays an important role in sustainable agriculture. On average, nitrogen-fixing legumes fix 100 kg of nitrogen per hectare per year.

Nodule organogenesis occurs through a complex molecular signaling process which is stimulated by the presence of compatible rhizobia. Functional nodules develop special structural features and perform unique metabolic reactions to enable rhizobial nitrogen fixation. Extensive metabolic adjustments are required for nodule function and during the co-evolutional processes of both partners, which are associated with profound gene expression reprogramming. A detailed understanding of these processes could underpin efforts to improve the efficiency of nitrogen fixation in legumes.

Recent advances in omics technologies have opened up a new strategy to address an old problem by using a more holistic approach to delineate the connections among the different nodulation and nitrogen fixation processes and pathways.

In this Research Topic the focus will be on understanding metabolic adjustments and gene expression reprogramming during nodulation, including but not limited to:
• The interplay of different regulatory mechanisms and signaling pathways in the initiation, development, maintenance, and senescence of nodules
• The interaction between different metabolic pathways inside nodules that affect the efficiency of nitrogen fixation
• The exchange of long-range signals between nodules and other plant parts
• The evolution of the efficient nitrogen-fixing systems by legume and rhizobia.

Keywords: Nitrogen Fixation, Nodules, Metabolic Adjustment, Gene Expression reprogramming, Omics, Signal Transduction, Long-Range Signals, Legume, Rhizobia

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