An Isoflavone Catabolism Gene Cluster Underlying Interkingdom Interactions in the Soybean Rhizosphere

Plant roots secrete various metabolites, including plant specialized metabolites, into the rhizosphere, and shape the rhizosphere microbiome, which is crucial for the plant health and growth. Isoflavones are major plant specialized metabolites found in legume plants, and are involved in interactions with soil microorganisms as initiation signals in rhizobial symbiosis and as modulators of the legume root microbiota. However, it remains largely unknown the molecular basis underlying the isoflavone-mediated interkingdom interactions in the legume rhizosphere. Here, we isolated sp. strain V35, a member of the that harbors isoflavone-degrading activity, from soybean roots and discovered a gene cluster responsible for isoflavone degradation named . The characterization of mutants and heterologously expressed Ifc enzymes revealed that isoflavones undergo oxidative catabolism, which is different from the reductive metabolic pathways observed in gut microbiota. We further demonstrated that the genes are frequently found in bacterial strains isolated from legume plants, including mutualistic rhizobia, and contribute to the detoxification of the antibacterial activity of isoflavones. Taken together, our findings reveal an isoflavone catabolism gene cluster in the soybean root microbiota providing molecular insights into isoflavone-mediated legume-microbiota interactions.