Plant response to early herbivory cues: how does a plant perceive an imminent attack?

Abstract

Plants and insect herbivores have a complex ecological relationship. Plants can react to direct signals from herbivores that indicate future attacks. When faced with herbivory damage or cues from insects, they frequently induce or prime their defenses. "Priming" of defense refers to a heightened state of alertness in plants triggered by external stimuli such as signals of stress caused by herbivores. Instead of immediately activating an induced defense, plants in a "priming" state respond more quickly and effectively when confronted with the actual attack. This research integrates studies on plant defense priming through detection of insect delivered cues. For instance, the sex pheromone of the coffee leaf miner Leucoptera coffeella triggers defense priming in coffee plants, reducing egg-laying and damage. Exposure to the synthetic pheromone 5,9-dimethylpentadecane altered the levels of defensive compounds, suggesting intricate chemical signaling in plant-insect interactions. Similarly, the domestication of Cucurbita pepo has altered its varieties' responses to insect pheromones like vittatalactone from Acalymma vittatum, with domesticated types showing an increase in defense mechanism compared to wild types. Furthermore, a meta-analysis highlights the broader phenomenon of plant priming of defense in response to herbivore stress. It has been shown that the activation of "priming" defense in plants is common and that both annual and perennial plants activate their "priming" defenses, as well as wild and domesticated plants. Additionally, we have seen that the duration of exposure to volatile cues, the experimental conditions, and the nature of the volatile compound modify the "priming" defense responses in plants. These findings collectively underscore the significance of plant-insect communication through chemical cues, offering insights into sustainable pest management, the evolutionary impact of domestication on plant defense, and new perspectives for future studies.