Emerald Ash Borer Infestation-Induced Elevated Negative Correlations and Core Genera Shift in the Endophyte Community of Fraxinus bungeana.

Simple Summary: The emerald ash borer (EAB, Agrilus planipennis Fairmaire) is currently a highly destructive forest pest, causing substantial economic losses. Ash species (Fraxinus spp.) are economically invaluable components of natural forests and urban environments. However, these trees have been severely damaged by EAB. Endophytes, which are prevalent in plants, are hypothesized to contribute to the complex relationships between insects and plants. However, research on the effect of EAB infestation on the community changes in endophytic fungi and bacteria in phloem of Fraxinus is scarce. To bridge this gap, we compare changes in fungi and bacteria diversity, community makeup, and the potential roles of various endophytic fungi and bacteria in both EAB-infested and uninfected Fraxinus bungeana trees. We observed an elevation in bacterial richness, without notable changes in diversity, whereas fungal richness and diversity remained unaffected. Furthermore, we identified four key microbial genera undergoing substantial shifts post-infestation. The functional roles of endophytic fungi and bacteria also exhibited changes, with a decline in beneficial activities and an emergence of potentially detrimental functions. Network analyses have shown elevated negative correlations and core genera shift in EAB-infected phloem. The findings of our study contribute to a better understanding of the complex interactions between plants, insects, and endophytic microorganisms. Endophytes, prevalent in plants, mediate plant–insect interactions. Nevertheless, our understanding of the key members of endophyte communities involved in inhibiting or assisting EAB infestation remains limited. Employing ITS and 16S rRNA high-throughput sequencing, along with network analysis techniques, we conducted a comprehensive investigation into the reaction of endophytic fungi and bacteria within F. bungeana phloem by comparing EAB-infested and uninfected samples. Our findings reveal that EAB infestation significantly impacts the endophytic communities, altering both their diversity and overall structure. Interestingly, both endophytic fungi and bacteria exhibited distinct patterns in response to the infestation. For instance, in the EAB-infested phloem, the fungi abundance remained unchanged, but diversity decreased significantly. Conversely, bacterial abundance increased, without significant diversity changes. The fungi community structure altered significantly, which was not observed in bacteria. The bacterial composition in the infested phloem underwent significant changes, characterized by a substantial decrease in beneficial species abundance, whereas the fungal composition remained largely unaffected. In network analysis, the endophytes in infested phloem exhibited a modular topology, demonstrating greater complexity due to an augmented number of network nodes, elevated negative correlations, and a core genera shift compared to those observed in healthy phloem. Our findings increase understanding of plant–insect–microorganism relationships, crucial for pest control, considering endophytic roles in plant defense. [ABSTRACT FROM AUTHOR]