Viruses, fungi and plants: Cross-kingdom communication and mutualism

Plants in natural ecosystems are symbiotic with fungal endophytes that have profound effects on host ecophysiology. In addition, symbiotic fungi may contain viruses that influence fungal physiology and alter the outcome of plant-fungal symbioses. For example, Dichanthelium lanuginosum is a plant that thrives in geothermal soils, tolerating root zone temperatures up to 60°C. Thermotolerance is dependent on the fungal endophyte Curvularia protuberata. Remarkably, the ability of C. protuberata to confer heat tolerance requires a double stranded RNA virus harbored by the fungus. When C. protuberata (containing the virus) and D. lanuginosum are grown independent of each other, they only tolerate temperatures up to 38°C. This is a clear example of how a symbiosis achieves something that the individual components cannot. In this chapter, we describe how this three-way symbiosis allows three organisms to survive in an environment they cannot tolerate on their own and explain what is known about the inter-organismal communication responsible for this mutualism.