Rhizobia use a pathogenic-like effector to hijack leguminous nodulation signalling

Area of Science:

• Plant-microbe interactions
• Molecular biology
• Symbiotic signaling

Background:

• Legume symbiosis with rhizobia is crucial for nitrogen fixation.
• Nod factors (NFs) and their receptors (NFRs) typically mediate this symbiosis.
• Pathogenic bacteria use type III secretion systems to deliver effectors.

Purpose of the Study:

• Investigate if rhizobia utilize pathogenic-like effectors to manipulate legume nodulation.
• Characterize the role of the rhizobial effector Bel2-5 in legume symbiosis.

Main Methods:

• Analysis of rhizobial effector Bel2-5 function in soybean nodulation mutants.
• Soybean root transcriptome analysis to understand Bel2-5's molecular targets.
• Genetic manipulation of rhizobial strains to assess nodulation ability.

Main Results:

• Rhizobial effector Bel2-5 can induce nitrogen-fixing nodules on soybean mutants lacking NF perception.
• Bel2-5 upregulates cytokinin signaling genes essential for nodule development.
• Bel2-5 downregulates ethylene and defense genes that inhibit nodulation.
• Introducing Bel2-5 into a non-nodulating strain restored nodulation ability.

Conclusions:

• Rhizobia have evolved and adapted pathogenic-like effector proteins to hijack legume nodulation signaling pathways.
• These effectors, like Bel2-5, promote symbiotic nodule formation by modulating plant hormone and defense responses.
• This finding reveals a novel mechanism of symbiotic plant-microbe interaction utilizing bacterial virulence factors.