Conserved secreted effectors contribute to endophytic growth and multi-host plant compatibility in a vascular wilt fungus

Fungal interactions with plant roots, either beneficial or detrimental, have a crucial impact on agriculture and ecosystems. The cosmopolitan plant pathogen Fusarium oxysporum (Fo) provokes vascular wilts in more than a hundred different crops. Isolates of this fungus exhibit host-specific pathogenicity, which is conferred by lineage-specific Secreted In Xylem (SIX) effectors encoded on accessory genomic regions. However, such isolates also can colonize the roots of other plants asymptomatically as endophytes or even protect them against pathogenic strains. The molecular determinants of endophytic multi-host compatibility are largely unknown. Here we characterized a set of Fo candidate effectors from tomato (Solanum lycopersicum) root apoplastic fluid; these Early Root Colonization effectors (ERCs) are secreted during early biotrophic growth on main and alternative plant hosts. In contrast to SIX effectors, ERCs have homologs across the entire Fo species complex as well as in other plant-interacting fungi, suggesting a conserved role in fungus-plant associations. Targeted deletion of ERC genes in a pathogenic Fo isolate resulted in reduced virulence and rapid activation of plant immune responses, while ERC deletion in a non-pathogenic isolate led to impaired root colonization and biocontrol ability. Strikingly, some ERCs contribute to Fo infection on the non-vascular land plant Marchantia polymorpha, revealing an evolutionarily conserved mechanism for multi-host colonization by root infecting fungi.