The dynamic mechanisms underpinning symbiotic Epichloë–grass interactions: implications for sustainable and resilient agriculture

Epichloë–grass associations are among the most well understood aboveground plant-microbe symbioses. Current attention has focused on understanding the molecular signals that underpin how these endophytes interact with their grass hosts to form natural and lifelong mutualistic symbioses. We review features of these symbioses, focusing on understanding host and endophyte responses, and their interactions which ultimately deliver important fitness benefits. One of the main selective forces of this symbiotic relationship are the endophyte expressed secondary metabolites. We examine how the host influences expression of these compounds and explore their function. Understanding the complex regulation of these symbioses at the cellular, biochemical, and molecular level is advancing and we show how such responses and subsequent outcomes are influenced by the evolutionary relationships between endophytes and hosts. We reveal a dynamic symbiosis that undergoes significant host reprogramming to accommodate its protective symbiont throughout the different stages of the host plant life cycle.