Host Metabolites Mediate Introgression-driven Assembly of Leaf Endophytic Fungi

The mutualistic relationship between plants and leaf endophytic fungi is crucial for facilitating host adaptability and stress resilience. However, the cascade effects of host genetic variation on plant adaptability via the mediation of the endophytic fungi remain unclear. Here, we conducted a landscape-scale investigation across natural oak distribution in China to disentangle how introgression alters the leaf metabolome and, consequently, affects the endophytic fungi-driven oak adaptability. Our results revealed a ‘dual adaptation strategy’, in which endophytic fungal diversity decreased while complexity of fungal co-occurrence network increased along with the introgression gradient. Simultaneously, the diversity of defensive metabolites increased with the rising introgression index, indicating enhanced oak adaptation to novel environments. Differential metabolite intensities and climate factors were key mediators in the fungal-driven adaptive process. Collectively, this work advances understanding of plant-microbe interactions in evolutionary ecology and highlights the importance of fungal community restructuring in plant adaptation to environmental change.