Plant volatile organic compounds as mediators of plant insect communication

Plants are sessile organisms exposed to a constant dialogue with various pests, insects, and microbes. After communication through various interactions (mutualism, predation, and parasitism), the plants trigger a range of volatile organic compounds (VOCs) through the modulation of the host gene. Plants responded to insect interactions both specifically and broadly. These interactions are controlled by various metabolic tracks such as the cytosolic mevalonic acid (MVA) pathway, plastidic methylerythritol phosphate (MEP) pathway, the phyto-oxylipin pathway, and shikimate pathways, where terpenoids, green-leaf volatiles (GLVs), and benzenoids/phenylpropanoids like VOCs are produced. Moreover, VOCs play a central role in chemical and visual communication, primarily by attracting pollinators and deterring herbivores, although in some cases, they may also manipulate herbivore behavior. The transmission of VOCs during insect attack is orchestrated via the signaling pathways of jasmonic acid (JA) and salicylic acid (SA). VOC biosynthesis is regulated at transcriptional, post-transcriptional, and epigenetic levels, involving transcription factors (TFs), miRNAs, long non-coding RNAs (lncRNAs), DNA methylation, chromatin remodeling, and histone modifications that modulate genes in VOC biosynthetic pathways. Subsequently, insects also developed approaches to conquer the plant hurdle as well as consequently established a plant–insect relationship. In this review, we concentrate on the roles of plant volatiles, including their production, functions, regulation, and defense system.