Molecular basis of specificity in host/fungus interactions

Fungal phytopathogens have evolved efficient mechanisms that enable them to exploit the plant nutrient reservoir for the purpose of growth and propagation. These are counteracted by the plants to arrest fungal development. Two general principles control the specificity of host/fungus interactions. In several cases, the interplay between fungus-produced toxins and either plant toxin targets or detoxification mechanisms determine the outcome of the interaction. An analogous principle appears to be operative in the opposite direction; deposition by plants of fungitoxic compounds that can be detoxified by pathogenic fungi. Presumably of more general importance is the recognition-based plant defense system. The ensuing resistance is frequently controlled by single genes in both interacting organisms. Originally observed in many crop plants at the sub-species level, it has recently also been described in wild plants and at the species level. The structures of disease resistance genes cloned to date from different plants allow the conclusion that the plant protective system against pathogens is based on a general principle that appears to be as effective as the animal disease protection system.