Speak, friend, and enter: signalling systems that promote beneficial symbiotic associations in plants

Reviews the molecular signalling by which legumes and rhizobia establish nodules — plant flavonoids inducing bacterial signalling molecules, their recognition by plant receptors, and the resulting developmental programme — alongside the related pathway used for mycorrhizal association.

Studied in

Plantae, Bacteria, Fungi

Sample size

review of nodulation and mycorrhizal signalling mechanisms

Nodulation proceeds through reciprocal chemical signalling and a controlled infection process, using a signalling pathway shared in part with the much older mycorrhizal symbiosis. The plant builds a new organ and controls admission at multiple stages.

• Mechanistic detail comes largely from a few model legumes and may not represent all nodulating plants.
• The review covers signalling; the ecological consequences of nodulation are treated elsewhere.

• Nitrogen fixation

  Fixation puts nitrogen into the plant, not directly into the ground. Whether the soil gains depends on what happens to that plant afterwards — and the plant pays for the whole arrangement in carbon.

• Nitrogen fixation

  The plant advertises chemically, the bacterium answers with a specific molecule, the plant recognises it and builds an organ to house it — while suppressing the immune response that would normally repel an infection.