Novel effectors identified in the apoplast of Cladosporium fulvum-infected tomato

Tomato leaf mold disease is caused by the biotrophic fungal pathogen Cladosporium fulvum. To colonize the leaf apoplast, C. fulvum secretes a collection of effector proteins that modulate host immune responses, as well as other proteins (e.g., carbohydrate-active enzymes or CAZys) that facilitate nutrient acquisition. In the presence of cognate Cf immune receptors, however, many of these proteins trigger immune responses that render the pathogen avirulent. Characterization of the C. fulvum apoplastic secretome is required to further understand the abovementioned processes, and to identify novel sources of resistance against this pathogen. We have used liquid chromatography–tandem mass spectrometry (LC–MS/MS) to identify 141 secreted and surface-associated fungal proteins present in apoplastic fluid harvested from compatible C. fulvum–tomato interactions. In addition to the known effectors identified in previous studies, this collection contains >70 new C. fulvum candidate effector (CfCE) proteins. Using a Potato virus X (PVX)-based expression system, we show that nine of these CfCEs, including Ecp11-1, which has homology to AvrLm3 and AvrLmJ1 of Leptosphaeria maculans, trigger cell death in particular wild accessions of tomato. Thus, our study has likely uncovered novel avirulence effectors of C. fulvum, as well as Cf immune receptors in wild tomato with new specificities against this pathogen. An overview of the C. fulvum apoplastic secretome will be presented.