Homologues of the Cladosporium fulvum effector proteins are present in Mycosphaerella species

Cladosporium fulvum is a non-obligate biotrophic fungal pathogen that causes leaf mould of tomato. Until now, ten effector proteins have been identified from C. fulvum that historically have been divided into avirulence (Avrs: Avr2, Avr4, Avr4E and Avr9) and extracellular proteins (Ecps: Ecp1, Ecp2, Ecp4, Ecp5, Ecp6 and Ecp7), and whose recognition in tomato is mediated by their cognate Cf (for C. fulvum) resistance proteins. Although demonstrated for only some of them, all Avrs and Ecps are assumed to be virulence factors. Avr2 is an inhibitor of apoplastic plant cysteine proteases, while Avr4 encodes a chitin-binding protein that protects chitin present in the cell walls of the fungus against the deleterious effects of plant chitinanes during infection. Ecp6 contains carbohydrate/chitin-binding LysM domains that putatively bind chitin fragments released from fungal cell walls during infection and prevents them from inducing basal defense responses during infection. Despite the fact that the interaction between C. fulvum and tomato is a model to study gene-for-gene based interactions, so far no homologues of the C. fulvum effector proteins have been identified in other fungal species. However, by mining of sequenced fungal genomes for homologous nucleotide sequences and protein motifs, we have now identified for the first time homologues of the C. fulvum Avr4, Ecp2 and Ecp6 effectors in other fungal pathogens, including Mycosphaerella fijiensis, Mycosphaerella graminicola and Cercospora nicotianae. Recently we have tested whether the three M. fijiensis homologues are truly functional homologues of the three C. fulvum effectors. We will report on the exciting results that have been obtained from these studies.