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Legume-specific recruitment of rhizobia by hyphae of arbuscular mycorrhizal fungi

Summary

Fungi in soil create underground networks connecting plant roots, acting like highways for bacteria called rhizobia. These bacteria need to find the right plant partner to help fix nitrogen from the air. The fungi transport special chemical signals from each plant that guide the bacteria to their correct host, improving crop nitrogen nutrition naturally.

Background

Legume-rhizobia symbiosis is crucial for sustainable agriculture due to nitrogen fixation capability. Rhizobia typically detect host legumes through flavonoids released by roots, but this recognition is limited to a few millimeters. Recent research shows arbuscular mycorrhizal fungi can extend this recognition distance beyond 15 cm by transporting flavonoids along their hyphae.

Objective

To investigate whether common mycorrhizal networks linking different legume species can transmit host-specific signals to guide rhizobia to their appropriate hosts. The study examined if Medicago truncatula and Glycine max connected via a CMN of Rhizophagus irregularis could direct their respective rhizobia symbionts to preferentially colonize compatible hosts.

Results

S. meliloti preferentially migrated toward M. truncatula (155±8 nodules in vitro, 71±82 in greenhouse), while B. diazoefficiens migrated toward G. max (13±3 nodules in vitro, 15±18 in greenhouse). M. truncatula-connected hyphae released DL-liquiritigenin, naringenin, sakuranetin, and 3,7-dimethylquercetin, while G. max-connected hyphae released daidzin, 6″-O-malonyldaidzin, irilone, and erylatissin A.

Conclusion

Common mycorrhizal networks function as a sophisticated navigation system using host-specific flavonoid chemical signals to orient rhizobia toward their compatible hosts. This mechanism improves nodulation efficiency and has potential agricultural applications for enhancing nitrogen fixation in legume crops.
  • Published in:ISME Journal,
  • Study Type:Experimental Study,
  • Source: PMID: 40396656, DOI: 10.1093/ismejo/wraf100
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