Homologs of Verticillium dahliae effector Ave1 contribute to virulence in fungal pathogens of diverse plant hosts

Verticillium dahliae is a fungal pathogen that causes vascular wilt in a broad range of host plants, including commercially important crops. The immune receptor Ve1, of which homologs are found in several host plants, confers resistance to Verticillium race 1 strains in tomato. Genome and RNA sequencing of V. dahliae race 1 and race 2 strains resulted in the identification of the highly expressed race 1-specific Ave1 gene that encodes the effector protein that is recognized by Ve1. Deletion of V. dahliae Ave1 does not only result in loss of recognition on Ve1 plants, but also makes the fungus less aggressive on tomato plants lacking Ve1. Homologs of Ave1 were mainly found in plants, but also in the fungal plant pathogens Fusarium oxysporum, Cercospora beticola and Colletotrichum higginsianum. To determine whether these Ave1 homologs can contribute to virulence, V. dahliae Ave1 deletion strains were complemented with the homologs of F. oxysporum, C. beticola and C. higginsianum, and tested for aggressiveness on tomato plants lacking Ve1. None of the tested homologs complemented virulence of V. dahliae Ave1 deletion strains. Subsequently, Ave1 deletion strains were generated in F. oxysporum, C. beticola and C. higginsianum to study their contribution to virulence in these pathogens. Ave1 homologs found in these three pathogens contribute to virulence. These data may suggest that Ave1 homologs of V. dahliae on the one hand, and F. oxysporum, C. beticola and C. higginsianum on the other hand, contribute to fungal virulence in different manners.