Undermining the cry for help: The phytopathogenic fungusVerticillium dahliaesecretes an antimicrobial effector protein to undermine host recruitment of antagonisticPseudomonasbacteria

During pathogen attack, plants recruit beneficial microbes in a “cry for help” to mitigate disease development. Simultaneously, pathogens secrete effectors to promote host colonization through various mechanisms, including targeted host microbiota manipulation. Here, we characterize the Av2 effector of the vascular wilt fungusVerticillium dahliaeas a suppressor of the cry for help. Inspired byin silicoantimicrobial activity prediction, we investigated the antimicrobial activity of Av2in vitro. Furthermore, its role inV. dahliaevirulence was assessed through microbiota sequencing of inoculated plants, microbial co-cultivation assays, and inoculations in a gnotobiotic plant cultivation system. We show that Av2 inhibits bacterial growth, and acts as a virulence factor during host colonization. Microbiota sequencing revealed involvement of Av2 in suppression ofPseudomonasspp. recruitment upon plant inoculation withV. dahliae, suggesting that Av2 suppresses the cry for help. We show that severalPseudomonasspp. are antagonistic toV. dahliaeand sensitive to Av2 treatment. We conclude thatV. dahliaesecretes Av2 to supress the cry for help by inhibiting the recruitment of antagonisticPseudomonasspp. to pave the way for successful plant invasion.