Assimilate transport and partitioning in fungal biotrophic interactions

Abstract

There are two major fungal biotrophic interactions with higher plants: pathogenic biotrophs such as mildews and rusts that cause substantial losses in crop yields, and mutualistic fungi that form mycorrhizas and aid the uptake of phosphate and other minerals from the soil with considerable agronomic benefits. Both are dependent on the plant for the supply of carbon, yet much remains to be resolved concerning the transport and partitioning of photoassimilates in these associations. In both associations, specialised membranes interfaces are formed which are considered to be the primary sites of nutrient transfer between plant and fungus. A range of solutes may cross these interfaces, although glucose appears to have a particularly important role. Molecular techniques are being used to identify the specific membrane transporters involved at the interface. The establishment of these biotrophic inter-actions also has a major effect on the metabolism and transport activity of the host plant that affects its source–sink balance. Increases in certain invertase activities and in hexose transporters are especially marked. Again, the introduction of molecular biology to these problems is beginning to provide the information on the cellular locations and coordination of these host cell responses that is required in order to understand how partitioning is regulated in these plant fungal interactions.