Were endophytes pre-adapted for defensive mutualism?

Abstract

Defensive mutualism in many grass endophytes involves herbivore deterrence, enhanced disease suppression and drought tolerance. According to our current understanding of the mechanisms, these defensive effects are unique features of the fungi and specific fungal qualities are responsible for each. We examined a selection of species of family Clavicipitaceae for defensive traits including ergot alkaloids and loline production and development of endophytic and epiphytic mycelial states. When features responsible for defensive effects are mapped onto phylogenetic trees showing relationships in the family, it is apparent that all defensive features of endophytic fungi pre-existed evolution of endophytism. We suggest that once endophytism evolved, the alkaloids and other fungal-mediated defensive features switched from previous functions to serve host defense functions. Defensive mutualism in the Clavicipitaceae endophytes naturally evolved through use of pre-existing fungal features after the step to endophytism was made. Keywords: Clavicipitaceae, defensive mutualism, endophytes, ergot alkaloids, loline alkaloids