Impact of Epichloë endophyte on rhizosphere resistome dynamics in wild barley and bluegrass.

Fungal endophytes are universally present in plant tissues to enhance stress resilience and growth of plants. They can change the microbial communities and functional characteristics of the rhizosphere without harming the host. However, the effect of their colonization on the distribution of antibiotic resistance genes (ARGs) and mobile genetic elements (MGEs) in rhizosphere soil remains largely unexplored. In the present study, the impact of the Epichloë bromicola fungal endophyte on the rhizosphere resistome structure and environmental factors in wild barley (Hordeum brevisubulatum) and bluegrass (Poa pratensis) plants was investigated. The rhizosphere ARGs and MGEs communities were characterized through metagenome analysis. Simultaneously, their relationship with key rhizosphere environmental variables was evaluated using redundancy analysis (RDA) and Mantel tests. The results revealed that infection altered the taxonomic distribution of ARGs and MGEs-carrying bacteria. Besides, it reduced the prevalence of the predominant genera Sphingomonas and Nocardioides, while increasing the contribution of the less prevalent genera Bradyrhizobium and Rubrivivax to multidrug efflux and macrolide resistance mechanisms. Co-occurrence network analysis showed decreased modularity, indicating a less compartmentalized resistome-mobilome under infection. The findings revealed that endophyte infection fundamentally restructured the rhizosphere resistome by changing environmental pressures and favoring stress-response mechanisms. The study provides novel insights into how fungal endophytes influence microbial resistome assembly and HGT processes, their role in environmental antibiotic resistance dissemination, and One Health resistome dynamics in the rhizosphere.