MSA Special Topics Award

Tall fescue (Schedonorus arundinaceus) is an agronomical important cool season grass that typically possesses the systemic symbiont, Epichloë coenophiala, a seed-borne fungal endophyte that significantly increases plant resistance to insects, nematodes, drought and stresses. The endophyte produces a cocktail of alkaloids that deter insects and perhaps nematodes, but includes ergot alkaloids that cause episodes of toxicosis to cattle, horses and other livestock. The resulting “fescue toxicosis” causes economic losses of ca. $1 billion annually in the U.S. Genome sequencing of E. coenophiala has revealed two largely duplicate clusters of ergot alkaloid biosynthesis genes, one of which (EAS1) is linked to the telomere at a chromosome end, whereas the other (EAS2) is not. This information prompted us to develop a chromosome-end “knockoff” technique that we used to trim off the EAS1 cluster. This technique involved transiently incorporating a selectable marker, which was then lost from the chromosome end to give a non-transgenic mutant. However, because some ergot alkaloids are still produced by that mutant, we propose to employ the CRISPR approach to eliminate the key gene for the first step in the pathway. Because E. coenophiala is asexual, doing so without leaving any transgene presents a challenge, which may be addressed using our “knockoff” technique with a destabilized selectable marker. If successful, the result will be precisely mutated but non-transgenic E. coenophiala strains for new tall fescue cultivars that are suitable for livestock while continuing to provide advantages to the plant. Furthermore, such a technique will be widely applicable to other fungi.