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Poster

Session: Session 2 Presenting Authors at Posters (Evens)

P-170 - Undermining the cry for help: The phytopathogenic fungus Verticillium dahliae secretes a novel antimicrobial to undermine host recruitment of antagonistic Pseudomonas bacteria

Thursday, July 17, 2025
13:30 - 15:15  
Location: Confex Hall 3
Effector Interference Mechanisms

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 fungus Verticillium dahliae as a suppressor of the cry for help. Deletion of Av2 compromises V. dahliae virulence in planta, as tomato plants inoculated with the wild-type strain developed stronger symptoms of disease than plants inoculated with the deletion strain. Intriguingly, inoculation experiments using a gnotobiotic plant cultivation system revealed that the virulence contribution of Av2 only occurs in the presence of a plant-associated microbiota. To investigate the effect of Av2 during host colonisation we conducted microbiota sequencing and found that Av2 is involved in suppression of the recruitment of Pseudomonas bacteria by plants that are challenged by Verticillium, suggesting that Av2 disrupts the cry for help response. Indeed, Av2 displays antimicrobial activity towards diverse Pseudomonas bacteria in vitro. Moreover, co-cultivation experiments revealed that Av2 deletion leads to reduced V. dahliae growth in the presence of particular Pseudomonas spp. Altogether, we conclude that V. dahliae secretes Av2 to supress the plant’s cry for help by inhibiting the recruitment of antagonistic Pseudomonas spp. to pave the way for disease establishment.