Mycorrhizal fungi alter root exudation to cultivate a beneficial microbiome for plant growth

Arbuscular mycorrhizal (AM) fungi traditionally form symbioses with most plant species. Although AM fungi have critical effects on microbial communities, the pathways showing how AM fungi shape rhizosphere bacterial communities and their functions are rarely explored. Through three systematic experiments, AM fungi-bacteria interactions were first investigated in the rhizosphere of Lotus japonicus, then the interactions were confirmed by a second experiment with wild-type and a mycorrhiza-defective mutant ljcbx of L. japonicus. The mechanisms were presented by adding core bacteria and AM fungi to the plant rhizosphere with the third experiment. We found that AM fungi-bacteria interactions enhanced host plant growth and identified a core bacterial group that uniquely enhanced host plant growth. Adding core bacteria and AM fungi promoted host growth and nutrient acquisition compared to adding AM fungi or core bacteria independently. Allelopathic substances secreted by AM fungal colonizing host roots to recruit the rhizosphere bacteria were detected by the multi-omics joint analysis, showing that arachidonic acid was the main allelopathic substance that affected AM fungi–bacteria interactions. Our findings provide direct evidence that mycorrhizal infection simulated root exudation, such as arachidonic acid, recruited a beneficial microbiome to the host rhizosphere, increasing plant growth and soil nutrient turnover.