Secrets of the fungus-specific potassium channel TOK family

Several families of potassium (K⁺) channels are found in membranes of all eukaryotes, underlining the importance of K⁺ uptake and redistribution within and between cells and organs. Among them, TOK (tandem-pore outward-rectifying K⁺) channels consist of eight transmembrane domains and two pore domains per subunit organized in dimers. These channels were originally studied in yeast, but recent identifications and characterizations in filamentous fungi shed new light on this fungus-specific K⁺ channel family. Although their actual function in vivo is often puzzling, recent works indicate a role in cellular K⁺ homeostasis and even suggest a role in plant-fungus symbioses. This review aims at synthesizing the current knowledge on fungal TOK channels and discussing their potential role in yeasts and filamentous fungi.