How Jasmonates Guide Plant Life, Death, and Defense
The air around a wounded plant is anything but silent; it is abuzz with chemical signals, and jasmonates are the powerful words in this vocabulary of survival.
You catch the sweet, heady fragrance of jasmine on a warm evening. This iconic scent, long captured in perfumes and teas, is more than just a pleasant aroma. It is the vapor of a sophisticated plant language, a chemical signal known as methyl jasmonate. For the jasmine flower, this compound is not for our enjoyment but is part of a complex hormonal communication system that guides everything from growth to defense. For decades, scientists have been decoding this language, uncovering a class of potent plant hormones known as jasmonates. These lipid-derived molecules are the master regulators of a plant's response to the world, enabling it to heal wounds, fight off infections, deter hungry insects, and even control its own reproduction.
The creation of jasmonates is a multi-step journey that begins in the chloroplast and ends in the cytoplasm and peroxisome. When a plant receives a signal, such as a caterpillar's bite or a pathogen's attack, the process is set in motion 1 4 .
Adds molecular oxygen to α-linolenic acid to form a fatty acid hydroperoxide 2 .
Reduces OPDA, a key step in forming the cyclopentanone structure of jasmonic acid 2 5 .
Finalize the synthesis of jasmonic acid through several cycles of fatty acid breakdown .
The pathway does not end with jasmonic acid (JA). This compound can be modified into various derivatives, such as the volatile methyl jasmonate (MeJA) or the highly bioactive jasmonoyl-isoleucine (JA-Ile) . It is these bioactive forms that are ultimately recognized by the plant's cellular machinery to trigger a response.
| Enzyme | Function | Location in Cell |
|---|---|---|
| Lipoxygenase (LOX) | Adds molecular oxygen to α-linolenic acid to form a fatty acid hydroperoxide 2 . | Chloroplast |
| Allene Oxide Synthase (AOS) | Converts the hydroperoxide into an unstable allene oxide 2 5 . | Chloroplast |
| Allene Oxide Cyclase (AOC) | Stabilizes the compound by cyclizing it to form OPDA, the first cyclic intermediate 2 5 . | Chloroplast |
| OPDA Reductase (OPR3) | Reduces OPDA, a key step in forming the cyclopentanone structure of jasmonic acid 2 5 . | Peroxisome |
| β-Oxidation Enzymes | Finalize the synthesis of jasmonic acid through several cycles of fatty acid breakdown . | Peroxisome |
Once synthesized, the bioactive jasmonate, primarily JA-Ile, sets in motion a precise molecular relay race within the cell. This signaling cascade is what translates the hormonal message into a genetic and physiological response.
The core of this pathway revolves around a simple but elegant concept: de-repression 8 . In the absence of JA-Ile, transcription factors like MYC2, which activate defense and other jasmonate-responsive genes, are held captive by repressor proteins called JAZs (Jasmonate ZIM-domain) 8 . When JA-Ile accumulates, it acts as a "molecular key":
JA-Ile is recognized by a receptor complex consisting of the F-box protein COI1 and JAZ proteins 8 .
This binding prompts the tagging of the JAZ repressors with ubiquitin, marking them for destruction by the proteasome, the cell's garbage disposal unit 8 .
With the JAZ repressors gone, the MYC2 transcription factors are set free. They can then bind to DNA and switch on the expression of hundreds of genes involved in plant defense and other jasmonate-regulated processes 8 .
This entire process, from receptor binding to protein degradation and gene activation, ensures that the plant's response is both rapid and robust, allowing it to adapt quickly to a changing and often hostile environment.
Much of our understanding of jasmonates stems from groundbreaking experiments. One of the most pivotal was conducted by Farmer and Ryan in 1990, which provided the first clear evidence of jasmonates' role in interplant communication and defense 4 .
The researchers hypothesized that a volatile signal released from wounded plants could travel through the air and induce defense responses in nearby, unwounded plants.
Tomato leaves were mechanically wounded to simulate insect herbivory.
Unwounded tomato plants were placed in the same enclosed chamber as the wounded plants, allowing air—and any volatile compounds—to circulate freely between them.
Other unwounded plants were kept in separate chambers away from the wounded plants.
The researchers then measured the accumulation of proteinase inhibitors (defensive proteins that disrupt insect digestion) in the leaves of the unwounded plants.
| Plant Group | Exposure | Level of Proteinase Inhibitors |
|---|---|---|
| Wounded Plants | N/A | High |
| Unwounded, Exposed | Air from wounded plants | High |
| Unwounded, Control | No air from wounded plants | Low |
This experiment was revolutionary. It identified methyl jasmonate as a potent airborne signal that could activate defense genes across individuals, proving that plants could "eavesdrop" on their neighbors' distress. It laid the foundation for understanding systemic acquired resistance and established jasmonates as central players in plant immunity.
Research into jasmonate signaling relies on a suite of specialized reagents and genetic tools. The following table details some of the essential items used by scientists in this field.
| Tool/Reagent | Function in Research |
|---|---|
| Jasmonate Biosynthesis Mutants (e.g., aos, opr3) | These Arabidopsis or tomato mutants are deficient in key biosynthetic enzymes. They are crucial for linking the loss of JA production to specific physiological defects, such as male sterility or compromised defense 4 . |
| JA-Signaling Mutants (e.g., coi1) | Mutants in the COI1 receptor are insensitive to jasmonates. They help researchers dissect the signal transduction pathway and identify which processes are truly JA-dependent 4 8 . |
| Coronatine | This bacterial toxin is a molecular mimic of JA-Ile and is a more potent and stable activator of the JA pathway. It is widely used to experimentally induce JA responses 4 . |
| JAZ Repressor Proteins | Key players in the JA signaling mechanism. Studying their degradation and interaction with MYC transcription factors is fundamental to understanding how JA responses are switched on 8 . |
| Systemin | An 18-amino-acid polypeptide hormone in tomato that is a potent inducer of JA biosynthesis. It is used to study the upstream signaling events that activate JA production in response to wounding 4 8 . |
The jasmonate pathway does not operate in isolation. It is part of a complex hormonal network, engaging in extensive "crosstalk" with other signaling pathways, such as those for salicylic acid (SA), ethylene, and auxin 1 6 . For instance, the JA and SA pathways often act antagonistically, allowing the plant to fine-tune its response based on whether it is facing a chewing insect (JA) or a biotrophic pathogen (SA) 4 .
Research continues to uncover new frontiers. A 2025 study highlights how applying methyl jasmonate to soil can reshape the microbial community, suppressing pathogens and boosting beneficial bacteria, thereby alleviating the negative effects of continuous cropping in chrysanthemums 7 . Furthermore, the once-elusive receptor for the wound signal systemin was recently identified as SYR1/SPR1, a leucine-rich repeat receptor kinase, filling a critical gap in our understanding of how the initial wound signal is perceived and transduced into JA biosynthesis 8 .
As we deepen our understanding of jasmonates, the potential applications grow. From developing crops with enhanced innate resistance to pests to creating more resilient agricultural systems in the face of climate change, deciphering the language of jasmonates holds the key to a more sustainable and productive future for agriculture.