nitrogen-fixing symbiosis

Edge evidence

• nodulation signalling enables nitrogen-fixing symbiosis RO:0002327

  Nod-factor signalling between rhizobia and legume hosts establishes the symbiosis.

  • DOI:10.1038/nrmicro2990 Oldroyd reviews symbiotic signalling establishing nitrogen-fixing plant-microbe associations.
• nitrogen-fixing symbiosis enables nitrogen fixation RO:0002327

  The symbiosis houses bacteroids that fix N2 inside root nodules.

  • DOI:10.1038/nrmicro.2017.171 Poole et al. describe the free-living-to-endosymbiont transition of rhizobia forming N2-fixing legume root nodules.
• flavonoids induces production of Nod factor (lipochitooligosaccharide)

  Legume flavonoid exudates induce rhizobia to produce Nod factors.

  • DOI:10.3389/fpls.2023.1284720 Legumes secrete flavonoids that induce rhizobia to produce Nod factors.
• Nod factor (lipochitooligosaccharide) enables nodulation signalling RO:0002327

  Perceived Nod factors initiate the nodulation signalling cascade.

  • DOI:10.3389/fpls.2023.1284720 Nod factors are perceived by Nod-factor receptors, triggering symbiotic signalling.
• leghemoglobin buffers microaerobic environment

  Leghemoglobin buffers oxygen concentration within nodules.

  • DOI:10.3389/fpls.2023.1284720 Leghemoglobins buffer the oxygen concentration within the nodules.
• nodule oxygen diffusion barrier maintains microaerobic environment

  A tightly packed cortical diffusion barrier limits oxygen flux into the nodule interior.

  • DOI:10.1038/s41564-024-01762-2 A diffusion barrier of tightly packed cells limits oxygen flux; the multilayered cortex functions as an adaptable oxygen diffusion barrier.
• microaerobic environment enables nitrogen fixation RO:0002327

  A low-oxygen environment is required for proper nitrogenase activity.

  • DOI:10.3389/fpls.2023.1284720 Symbiotic nitrogen fixation requires a low-oxygen environment for proper activity of nitrogenase.
• nitrogenase complex enables nitrogen fixation RO:0002327

  The nitrogenase complex reduces N2 to NH3 (16 ATP per N2).

  • DOI:10.1017/S1062798724000309 The nitrogenase reaction consumes 16 ATP in the reduction of N2 to NH3.
• organic acids enables nitrogen fixation RO:0002327

  The plant supplies organic acids as reductant to intracellular bacteroids fueling fixation.

  • DOI:10.1038/s41564-024-01762-2 The plant transfers reductant, typically organic acids, from plant cells to intracellular rhizobia.
• iron availability is required for nitrogenase complex

  Iron is an essential cofactor for nitrogenase assembly and leghemoglobin function.

  • DOI:10.1093/pcp/pcae128 Fe is essential as a cofactor for leghemoglobin and for assembling the nitrogenase complex.