Contribution of fungal loline alkaloids to protection from aphids in a grass-endophyte mutualism

Fungal endophytes provide grasses with enhanced protection from herbivory, drought, and pathogens. The loline alkaloids (saturated 1-aminopyrrolizidin es with an oxygen bridge) are fungal metabolites often present in grasses w ith fungal endophytes of the genera Epichloe or Neotyphodium. We conducted a Mendelian genetic analysis to test for activity of lolines produced in pl ants against aphids feeding on those plants. Though most loline-producing e ndophytes are asexual, we found that a recently described sexual endophyte, Epichloe festucae, had heritable variation for loline alkaloid expression (Lol(+)) or non-expression (Lol(-). By analyzing segregation of these pheno types and of linked DNA polymorphisms in crosses, we identified a single ge netic locus controlling loline alkaloid expression in those E, festucae par ents. We then tested segregating Lol(+) and Lol(-) full-sibling fungal prog eny for their ability to protect host plants from two aphid species, and ob served that alkaloid expression cosegregated with activity against these in sects. The in planta loline alkaloid levels correlated with levels of anti- aphid activity. These results suggested a key role of the loline alkaloids in protection of host plants from certain aphids, and represent, to our kno wledge, the first Mendelian analysis demonstrating how a fungal factor cont ributes protection to plant-fungus mutualism.