Tall fescue (Lolium arundinaceum) forms a mutualistic relationship with the fungal endophyte Neotyphodium coenophialum. The endophyte provides constitutive resistance to herbivores through the production of alkaloid compounds. Moreover, herbivore attack induces elevated synthesis of loline alkaloids; that is, the fungus also provides wound-inducible resistance for its host. Jasmonic acid and its conjugates are key signaling compounds in many plant species and play a role systemically in the up-regulation of defensive compounds within plants following attack by pathogens or herbivores. The purpose of our study was to determine if and how the plant and fungus respond to methyl jasmonate (MJ) exposure and if these responses interact in antagonistic or synergistic ways.
Results/Conclusions
Plants were exposed to MJ via gaseous diffusion within an environmental chamber. Response to MJ was assessed using an herbivore bioassay, GC-MS to quantify alkaloids, and real time RT-PCR to quantify RNA from a loline alkaloid biosynthesis gene. We found that MJ hindered infected tall fescue's resistance against insect herbivores by down-regulating transcription of the lolC gene. We found the opposite for uninfected tall fescue; its exposure to MJ resulted in a significant increase in resistance to an insect herbivore, apparently through stimulating defense compounds produced by the plant. These results indicate that MJ induces the production of defensive compounds by uninfected tall fescue when it lacks fungal infection while it compromises the ability of the fungus to provide protection from herbivores.
