THE TOMATO–CLADOSPORIUM FULVUM INTERACTION: A Versatile Experimental System to Study Plant-Pathogen Interactions

Over the past 20 years, the interaction between the biotrophic fungal pathogen Cladosporium fulvum and tomato has developed into a versatile experimental system for molecular plant pathology and resistance breeding. This interaction provided the resources for cloning of fungal avirulence genes for the first time and interesting clues on recognition of their extracellular products by tomato, as well as mechanisms employed by the fungus to circumvent this recognition. A wealth of information has become available on the structure and genomic organization of Cf resistance genes. The occurrence of many clustered Cf homologues allows the generation of new genes with additional recognitional specificities by reshuffling. It is anticipated that potentially all proteins secreted by C. fulvum are recognized by one or more individuals in a population of tomato genotypes, a hypothesis that has been experimentally confirmed. The future challenge will be to elucidate the mechanisms of perception of avirulence factors and the subsequent signaling eventually leading to activation of host defense responses.