COEVOLUTION AND GENETIC DIVERSITY IN GRASS-ENDOPHYTE

Symbioses between cool-season grasses (Subfamily Pooideae) and endophytic fungi in the genera Epichloë and Neotyphodium straddle a continuum of interactions from antagonistic to highly mutualistic. Although these two genera of endophytes are closely related, Neotyphodium endophytes are strictly seed-transmitted and provide many physiological and defensive benefits to their hosts, while Epichloë spp. have an obligately sexual contagious stage wherein host inflorescences are replaced by fungal sexual structures (stromata), effectively sterilizing the plant. Between these two extremes of interactions are Epichloë spp. with a “mixed ” strategy, where some grass tillers are sterilized while others develop normally and yield healthy endophyte-infected seeds. These symbioses offer a unique opportunity to dissect evolutionary mechanisms that may drive movement along this continuum. The research presented characterizes distinct hybridization processes in endophytes and grasses that result in the generation of astounding genetic diversity for the symbiosis. Interspecific hybridization via hyphal anatomosis is a common feature of Neotyphodium endophytes, and may promote mutualism by combining suites of defensive alkaloid genes and ameliorating the advers