Transcriptomic evidence of interspecies systemic resistance induction via common mycorrhizal networks

Plants face persistent biotic pressures from pathogens and herbivores, necessitating effective defense mechanisms. Common mycorrhizal networks (CMNs), formed by arbuscular mycorrhizal fungi, facilitate inter-plant defense signal transmission. However, little is known about interspecies signal transmission through CMNs. This study aimed to investigate whether defense signals can be transferred from pathogen-infected white clover (Trifolium repens) to neighboring healthy perennial ryegrass (Lolium perenne) via CMNs and to assess the subsequent activation of disease-resistance responses in ryegrass at the transcriptional level. A dual-chamber experimental setup was used, in which white clover served as the donor plant and perennial ryegrass was the receiver plant. The results showed that pathogen-induced defense signals can be transferred from infected donor clover to healthy ryegrass plants through CMNs, inducing the expression of resistance genes in the neighboring plants, especially TRINITY_DN52759_c0_g1 (disease resistance protein RGA2). Importantly, the upregulated expression of defense genes was closely related to CAT activity. These factors enhance the defense response of neighboring healthy plants against potential pathogens. Although the pathogenic microbe evaluated is non-pathogenic to ryegrass, the signal transmission mechanism may apply to scenarios with shared threats. In addition, we identified gene modules significantly associated with CAT through weighted gene co-expression network analysis and screened key network genes (TRINITY_DN29267_c0_g1, TRINITY_DN37961_c0_g1, TRINITY_DN74958_c0_g2, TRINITY_DN7515_c0_g1, TRINITY_DN7587_c0_g6) in co-expression networks, which potentially play critical roles in defense responses. The findings suggest that CMNs serve as vital conduits for interplant defense signal transfer, facilitating early warning and defense activation against potential pathogens.