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.