Do the fungal homologs of Verticillium dahliae effector Ave1 act as virulence factors?

Verticillium species cause vascular wilt disease in over 200 plant hosts, including economically important crops. In tomato, the Ve1 immune receptor confers resistance to race 1 strains of V. dahliae, but not to race 2. By population genome sequencing of race 1 and race 2 strains, the effector that is recognized by Ve1 was recently identified as Ave1 (Avirulence on Ve1 tomato). Ave1 has homology to plant natriuretic peptides that are regulators of homeostasis, and acts as a virulence factor on tomato plants that lack Ve1 as well as on Arabidopsis. In addition to plants, Ave1 homologs were also found in a few fungal pathogens, including Fusarium oxysporum, Cercospora beticola and Colletotrichum higginsianum, as well as in the bacterial plant pathogen Xanthomonas axonopodis. Co-expression of V. dahliae Ave1 and tomato Ve1 in Nicotiana tabacum resulted in the activation of a hypersensitive response. Remarkably, also co-expression of some of the Ave1 homologs with Ve1 activated a hypersensitive response. Here, we evaluate whether the various pathogen-derived Ave1 homologs are virulence factors. Expression of the Ave1 homologs of Fusarium, Cercospora and Colletotrichum during infection on tomato, sugarbeet, and Arabidopsis, respectively, was analysed. To investigate the potential role of the Ave1 homologs in virulence, a V. dahliae Ave1 deletion mutant was complemented with the Ave1 homologs of Fusarium, Cercospora and Colletotrichum, and tested for full aggressiveness on tomato. Finally, targeted gene deletion was pursued in Fusarium, Cercospora and Colletotrichum and the corresponding deletion strains were inoculated on tomato, sugarbeet, and Arabidopsis, respectively.