A single Verticillium dahliae effector determines pathogenicity on tomato by targeting auxin response factors

SUMMARYVerticillium dahliae is a xylem-invading fungal pathogen that causes devastating vascular wilt diseases on hundreds of plant hosts, including tomato (Solanum lycopersicum). Although individual V. dahliae strains are typically characterized by their broad host range, differential pathogenicity occurs on nearly all hosts. Currently, the molecular basis underlying such pathogenicity differences remains unknown. We used comparative genomics to identify a single effector gene that specifically occurs in tomato-pathogenic V. dahliae strains and is expressed during tomato colonization. Functional analyses showed that this Tom1 effector governs pathogenicity on tomato, as Tom1 deletion prohibited tomato colonization, while introduction of Tom1 into non-pathogenic V. dahliae or into saprophytic sister species V. tricorpus and V. nubilum resulted in disease. Through proteomics-based approaches, auxin response factors (ARFs) were identified as in planta targets of Tom1. Intriguingly, repression of SlARF2a expression by virus-induced gene silencing fully impaired V. dahliae colonization of tomato, solidifying its role as susceptibility target.Collectively, our findings indicate that a single effector, Tom1, mediates pathogenicity of V. dahliae on tomato by targeting auxin response factors.