MOLECULAR ASPECTS OF AVIRULENCE GENES OF THE TOMATO PATHOGEN CLADOSPORIUM-FULVUM

Host genotype specificity in interactions between biotrophic fungal pa thogens and plants in most cases complies with the gene-for-gene model . Success or failure of infection is determined by the absence or pres ence of complementary genes, avirulence and resistance genes, in the p athogen and the host plant, respectively. Resistance, expressed by the induction of a hypersensitive response followed by other defence resp onses in the host, is envisaged to be based on recognition of the path ogen, mediated through direct interaction between products of avirulen ce genes of the pathogen (the so-called race-specific elicitors) and r eceptors in the host plant, the putative products of resistance genes. The interaction between the biotrophic fungus Cladosporium fulvum and its only host, tomato, is a model system to study fungus-plant gene-f or-gene relationships. Here we review research on isolation, character ization, and biological function of two race-specific elicitors AVR4 a nd AVR9 of C. fulvum and cloning and regulation of their encoding gene s.