Epichloe Fungal Endophytes and Plant Defenses: Not Just Alkaloids

Although the role of fungal alkaloids in protecting grasses associated with Epichloe fungal endophytes has been extensively documented, the effects of the symbiont on the host plant's immune responses have received little attention. We propose that, in addition to producing protective alkaloids, endophytes enhance plant immunity against chewing insects by promoting endogenous defense responses mediated by the jasmonic acid (JA) pathway. We advance a model that integrates this dual effect of endophytes on plant defenses and test its predictions by means of a standard meta-analysis. This analysis supports a role of Epichloe endophytes in boosting JA-mediated plant defenses. We discuss the ecological scenarios where this effect of endophytes on plant defenses would be most beneficial for increasing plant fitness.