Many species of animals, particularly those with known predators, can signal each other of imminent dangers through a variety of techniques, ranging from scent to sound. A new study led by Tokyo University of Science has recently argued that plants can “sound alarms” under threats of attack too, and revealed the epigenetic mechanisms of volatile-signal-induced activation of defense genes in specimens threatened by herbivorous predators.
Previous studies have shown that, when grown close to mint plants, soybean and field mustard plants often display a heightened response to herbivore pests by activating defense genes in their leaves as a result of “eavesdropping” on mint volatiles. When mint leaves get damaged by a predator, they emit chemical signals that soybean and field mustard detect, leading them to quickly activate their anti-herbivore defense systems. To clarify this mechanism, a team of researchers from various Japanese institutions examined these responses in Arabidopsis thaliana, a model plant used widely in biological studies.
“Surrounding undamaged plants exposed to odors emitted from plants eaten by pests can develop resistance to the pests. Although the induction of the expression of defense genes in odor-responsive plants is key to this resistance, the precise molecular mechanisms for turning the induced state on or off have not been understood,” explained study co-author Gen-ichiro Arimura, an associate professor of Biology at Tokyo University of Science. “In this study, we hypothesized that histone acetylation, or the so-called epigenetic regulation, is involved in the phenomenon of resistance development.”
Professor Arimura and his colleagues exposed the plants to β-ocimene, a volatile organic compound that is often released by plants in response to predatory attacks, and discovered that defense traits were induced in Arabidopsis leaves through epigenetic mechanisms, or processes of gene regulation occurring due to external environmental influences.
More specifically, the volatile chemicals released by the damaged plants enhanced histone acetylation and the response of defense gene regulators, such as the ethylene response factor genes “ERF8” and “ERF104,” together with a specific set of histone acetyltransferase enzymes (HAC1, HAC5, and HAM1).
Clarifying the epigenetic mechanisms behind plant defense can have important applications in organic cultivation systems, by helping cultivators increase their crops’ pest resistance and effectively reduce the current massive dependence on pesticides.
“The effective use of plants’ natural survival strategies in production systems will bring us closer to the realization of a sustainable society that simultaneously solves environmental and food problems,” concluded Professor Arimura.
The study is published in the journal Plant Physiology.