Plants finetune immune signaling, metabolite and nutrient levels to configure a healthy leaf microbiota

Pathogens and pests threaten global food security, causing billions in crop losses annually.Two emerging strategies to address this involve engineering plant microbiotas and designing microbiota-shaping metabolite formulations.Achieving these goals requires a mechanistic understanding of plant-microbiota-pathogen interactions.While plant immunity gates a healthy leaf microbiota and infection alters microbiota composition, the immune effector molecules involved remain unclear.Using bacterial synthetic communities, 16S profiling, metabolomics, transcriptomics, and binary interaction assays, our research shows that the immune-suppressing pathogen Pseudomonas syringae disrupts microbiota by competing with Firmicutes and Actinobacteria for iron and other nutrients.A plant mutant mimicking pathogenesis exhibits decreased iron levels and increased expression of iron starvation response genes.In planta metatranscriptomics of a 48-member synthetic community further revealed enrichment of iron starvation genes in microbiota.Our findings suggest iron and plant metabolites act as immune effectors shaping microbiota, and pathogens disrupt these molecules to promote disease.