Role of fungal endophytes on mycorrhizal-plant association and its impact on plant fitness

Throughout their evolutionary history, plants have established fine-tuned interactions with microorganisms present in their environment. An example of these interactions is the association with diverse groups of endophytes. Microbial endophytes also can modulate associations between plants and other symbionts, like arbuscular mycorrhizal fungi (AMF). A sizable body of evidence has shown the beneficial effects of AMF and/or fungal endophytes on plant fitness and development. Additionally, AMF and fungal endophytes living in the same plant may reciprocally interact, with remarkable consequences for the physiology of the host. In this chapter, we overview the state-of-the-art analysis of multipartite microbial interactions, with a special focus on how belowground endophytes (dark septate endophytes and phosphate-solubilizing fungi) and aboveground endophytes (vertically transmitted endophytes like Epichloë and horizontally transmitted endophytes) interact with AMF and how these plant-microbial interactions affect AMF establishment, development, efficiency, and their overall impact on plant fitness.