Common mycelial network mediated inter-plant signals modulate plant biotic stress responses and defence against foliar pathogens

Arbuscular mycorrhizal fungi (AMF) colonize multiple plant hosts and form common mycelial networks (CMNs) that link multiple plants in nature. CMNs are hypothesised to function as a highway for inter-plant information exchange to modulate plant biotic and abiotic stress responses.

Here we used AMF Rhizophagus irregularis to inter-connect two Medicago truncatula plants and explored the effect of known plant defence elicitor on pathogen tolerance of AMF-connected inter-plant signal receivers. We analysed Medicago leaf metabolites and emitted volatiles together with transcriptome data to compare responses of the inter-plant signal receivers with intact and cut CMN.

The integrity of CMN significantly affected inter-plant signal receiver responses. Plant defence and signalling pathways were enriched with receiver transcripts that are uniquely changing in the intact vs interrupted CMN along with distinct production of plant isoprenoids – volatile monoterpenes and triterpene saponins. Furthermore, receivers of CMN-mediated signals from stressed senders display increased resistance to Fusarium sporotrichoides and susceptibility to Botrytis cinerea .

Our results highlight CMN contribution to receiver plant responses which may encode susceptibility and resistance factors to different plant pathogens. Future dissection of the mechanisms involved in inter-plant signal decoding will yield novel discoveries on genetic regulation of inter-plant defence priming under pathogen attack.