De-constructing a mutualist : how the molecular blueprints of model symbiotic fungi are changing our understanding of mutualism

A fascinating example of a class of organisms able to control and restructure their environment are the mutualistic ectomycorrhizal (ECM) fungi. These fungi are present in the soils of most forest environments, where they colonize tree roots to exchange nutrients that supports both tree and fungal growth. Very few plant defenses are raised against the invading hyphae of ECM fungi, likely due to the manipulation of conserved signaling protein ‘hubs’ within the host root. In this chapter, we will consider the role of both plant and ECM fungal signals involved in the structuring of their environment during the colonization of plant tissues. We will use as a basis of comparison the role of secreted proteins in pathogenic interactions in performing similar tasks. The chapter will conclude with an overview of the different signaling hubs that ECM fungi must overcome or control to establish a nutrient exchange between both partners—an exchange critical to the sustainability of our forest ecosystems.