Fungal Avirulence Genes and Plant Resistance Genes: Unraveling the Molecular Basis of Gene-for-gene Interactions

Abstract

The interaction between tomato and C. fulvum has proven to be an excellent model system to dissect a host-pathogen interaction that complies with the gene-for-gene model at the molecular level. Cloned avirulence and resistance genes provide valuable tools to study the molecular genetic mechanisms determining race-specific resistance. The transposon tagging approach, which has been very effective in bacteria to identify and characterize different types of genes, can also be employed to isolate fungal avirulence genes, as active transposons have been described in numerous fungi, such as Fusarium oxysporum. The interaction between the biotrophic fungus Cladosporium fulvum and tomato (Lycopersicon esculentum), has been studied extensively as a model system for plant-fungus gene-for-gene relationships. The fungal pathogen Magnaporthe grisea causes blast of rice and different grass species. The molecular basis of host specificity in the rice blast disease has been studied intensively in recent years. Many Phytophthora species produce a family of small extracellular proteins of ca. 10 kDa named elicitins, which induce necrosis and other defense responses particularly on tobacco and some radish and turnip cultivars. Transposon tagging involves the inactivation of a resistance gene by insertion of a transposable element.