Hydroxylated Monoterpenes Act as Immune Amplifiers in Tomato Defense Against Bacterial Pathogens
Researchers have found that hydroxylated monoterpenes (HMTPs), volatile compounds emitted by tomato plants during bacterial infection, act as internal signals that trigger and self-amplify immune defenses. These compounds activate multiple defense pathways—including jasmonate, salicylic acid, calcium, and reactive oxygen species signaling—and promote their own production in a self-reinforcing loop. The findings reveal a previously uncharacterized mechanism by which plants can sustain and escalate immune responses without continuous pathogen stimulation.
A study published on bioRxiv demonstrates that hydroxylated monoterpenes (HMTPs), volatile organic compounds released by tomato plants during resistant interactions with the bacterium Pseudomonas syringae, function as endogenous mimics of pathogen attack. Using α-terpineol as a representative HMTP, the researchers showed that these volatiles activate MAP kinase, calcium, and reactive oxygen species (ROS) signaling cascades, while also promoting the accumulation of the defense hormones jasmonate and salicylic acid. Notably, HMTPs were found to induce stomatal closure—a key physical barrier against bacterial entry—independently of abscisic acid, the hormone typically associated with this response. The study further established a self-amplifying feed-forward loop: ROS and jasmonate signaling are required for HMTP biosynthesis, and HMTPs in turn promote their own accumulation. In vitro experiments showed that oxidative conditions drive chemical interconversion among HMTPs, favoring the buildup of more bioactive hydroxylated forms, and deuterium-labeling experiments confirmed that volatile interconversion also occurs within living plant tissue.
What's missing
As a preprint, this study has not yet undergone formal peer review, so its findings should be considered preliminary. The research does not address whether the self-amplifying HMTP mechanism operates similarly in other plant species or under field conditions, nor does it examine potential fitness costs to the plant of sustaining such a self-reinforcing immune loop.
What different sources said
- bioRxivCenter
Hydroxylated monoterpenes mimic bacterial attack to trigger jasmonate-dependent self-amplifying immunity in tomato
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