Aesculetin-mediated recruitment of denitrifying microbiota by resistant rapeseed suppresses Plasmodiophora brassicae via nitrate depletion

Clubroot, caused by the protist pathogen Plasmodiophora brassicae, is a major threat to cruciferous crop production worldwide. Although plant microbiota is known to influence disease outcomes, the mechanisms underlying microbiota-mediated resistance remain unclear. Here, we investigated the role of plant microbiota in clubroot resistance using two Chinese rapeseed cultivars carrying resistance genes introduced through breeding and their susceptible parental lines. Microbiome profiling revealed that P. brassicae infection altered root and rhizosphere bacterial communities, with resistant cultivars displaying distinct assemblages. Functional prediction indicated an enrichment of denitrifying bacteria in the roots of resistant plants following pathogen challenge. Key denitrifying strains were isolated and assembled into a synthetic microbial community (SynCom18), which significantly suppressed clubroot development under both controlled and field conditions. In addition to reducing disease severity, microbial treatments improved agronomic traits, including yield and seed quality. Mechanistic analysis revealed a positive correlation between soil nitrate levels and disease severity. Denitrifying strains and SynCom18 likely suppressed the development of P. brassicae and enhanced plant immunity by reducing soil nitrate levels by ~39.4%. Metabolomic profiling revealed that aesculetin, as a dominant metabolite that is produced by resistance roots and excreted into the rhizosphere to recruit denitrifying bacteria. Our findings show that pathogen-infected clubroot-resistant rapeseed cultivars secrete aesculetin to recruit nitrate-depleting bacteria for resistance against P. brassicae. This study elucidates a tripartite microbiota-pathogen-soil nutrient interaction and provides a sustainable biocontrol strategy for cruciferous crops.