Abstract
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 fungus Laccaria bicolor on the nonmycorrhizal plant Arabidopsis thaliana. We used the cabbage looper Trichoplusia ni and bacterial pathogen Pseudomonas syringae pv. tomato DC3000 (Pto) as readouts for ISR on Arabidopsis. We found that root inoculation with L.bicolor triggered ISR against T.ni and induced systemic susceptibility (ISS) against the bacterial pathogen Pto. We found that L.bicolor-triggered ISR against T.ni was dependent on jasmonic acid signaling and salicylic acid biosynthesis and signaling. Heat-killed L.bicolor and chitin were sufficient to trigger ISR against T.ni and ISS against Pto. The chitin receptor CERK1 was necessary for L.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.
Highlights
Plants associate with complex communities of microorganisms
Arabidopsis seedlings were treated with L. bicolor (Methods), and the rosettes were challenged with T. ni larvae 3 weeks later
We found that L. bicolor treatment of roots resulted in significant induction in shoots of jasmonic acid (JA)-Ile marker genes including
Summary
Interplay of host and microbial genotype determine whether the outcome of specific plant-microbe interactions is beneficial or detrimental to plant health[1,2,3]. Plants possess receptors to sense potential pathogens including transmembrane pattern-recognition receptors that recognize conserved microbe-associated molecular patterns (MAMPs), and intracellular receptors that directly or indirectly recognize effectors to help limit pathogen growth[4,5]. In addition to local immune mechanisms, root-associated microbes can induce systemic resistance (ISR) against a diverse spectrum of above-ground threats[2,10]. While the mechanisms by which plants perceive MAMPs and effectors are well understood, there is a more limited understanding of the mechanisms by which plant perceive the microbes that trigger ISR
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