Homeostasis of trace elements in mycorrhizal fungi

Ectomycorrhizal (ECM) fungi largely determine the element offer at the fungusroot interface, although they do not take over the plant nutrient uptake system. In complex forest soils, trees undoubtedly benefit from the well-adapted nutrient acquisition strategies evolved in the huge diversity of ECM fungi that occupy the numerous niches in the different soil types. As with all organisms, mycorrhizal fungi feature genes encoding proteins involved in trace element acquisition, storage and remobilization to assure cellular homeostasis regardless of natural external fluctuations. A constant cellular concentration of essential trace elements is required to secure growth and reproduction and to overcome toxicity. Transcriptome analysis is the most prominently used approach to identify genes and gene products involved in trace element homeostasis. Imbalances in the cellular homeostasis of trace elements, even brief ones, produces reactive oxygen species (ROS). ROS can be generated directly by redox-active elements or indirectly by redox-inactive elements.