Ectomycorrhizal fungi induce systemic resistance against insects on a non-mycorrhizal plant in a CERK1-dependent manner.

Below-ground microbes can induce systemic resistance against foliar pests and pathogens on diverse plant hosts. The prevalence of induced systemic resistance (ISR) among plant-microbe-pest systems raises the question of host specificity in microbial induction of ISR. To test whether ISR is limited by plant host range(,)we tested the ISR-inducing ectomycorrhizal fungusLaccaria bicoloron the nonmycorrhizal plantArabidopsis thaliana. We used the cabbage looperTrichoplusia niand bacterial pathogenPseudomonas syringaepv.tomatoDC3000 (Pto) as readouts for ISR onArabidopsis. We found that root inoculation withL. bicolortriggered ISR againstT. niand induced systemic susceptibility (ISS) against the bacterial pathogenPto. We found thatL. bicolor-triggered ISR againstT. niwas dependent on jasmonic acid signaling and salicylic acid biosynthesis and signaling. Heat-killedL. bicolorand chitin were sufficient to trigger ISR againstT. niand ISS againstPto. The chitin receptor CERK1 was necessary forL. bicolor-mediated effects on systemic immunity. Collectively our findings suggest that some ISR responses might not require intimate symbiotic association, but rather might be the result of root perception of conserved microbial signals.