Biotrophic interfaces and nutrient transport in plant fungal symbioses

Anton de Bary 1879 introduced the term symbiosis to refer to organisms 'living together' and, in this broad sense, it encompasses situations ranging from parasitic, to mutualistic, During many symbiotic associations the two partners exist in close contact with each other and in some cases specialized biotrophic interfaces develop. These are thought to be the primary sites of nutrient transfer between the symbionts, Powdery mildew and rust fungi are obligate biotrophs which form parasitic symbiotic associations with plants, while the obligately biotrophic arbuscular mycorrhizal fungi form mutualistic symbioses with plants. In both of these symbioses, specialized membrane interfaces are formed. Investigations of the structure and function of these interfaces have been ongoing for a number of years, but have been hampered by the problems of working with obligate biotrophs and by the fact that these interfaces may form only deep inside living tissue. The recent use of immunocytological and molecular biological methods has begun to provide insight into the molecular structure of the interface and of transport proteins potentially involved in nutrient transfer.