Chemotypic diversity of epichloae, fungal symbionts of grasses

Abstract

Abstract The epichloid fungi – comprising sexual Epichloe species and asexual Neotyphodium species – are symbionts of cool-season grasses (subfamily Pooideae), mostly vertically transmissible (seedborne), and well known for production of anti-herbivore alkaloids. Four classes of alkaloids are known to be produced by epichloae: lolines (saturated aminopyrrolizidines), indole–diterpenes, ergot alkaloids, and peramine. There is a wide range of chemotypic diversity among and even within epichloid species. At the molecular level, this diversity may in part reflect the telomeric association of two of the four alkaloid biosynthesis gene clusters. Ecologically, the chemotypic diversity within species may reflect frequency-dependent selection for the alkaloids, which provide defences against insects and, in some cases, vertebrates, but can be expensive to produce. Interspecific hybridization, common among asexual epichloae, can pyramid the alkaloid biosynthesis genes. Compared to sexual epichloae, many asexual epichloae produce high levels of alkaloids – particularly lolines – suggesting that strict vertical transmission selects for enhanced capability of host protection.