Avirulence and resistance genes in the Cladosporium fulvum-tomato interaction.

The fungus Cladosporium fulvum infects tomato and secretes various proteins that are recognized by resistant plants that respond with a hypersensitive response. Strains of the fungus that escape recognition by tomato are virulent. Resistance genes in tomato, either directly or indirectly involved in recognition of the fungal proteins, encode extracellular membrane-anchored, leucine-rich repeat proteins, which occur in gene clusters. Much progress has been made in our understanding of the evolution of recognitional specificities in the host plant.