Phytohormone-mediated plant defense for sustainable insect pest management: mechanisms, advances, and future perspectives

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Deciphering the molecular and cellular crosstalk among plants, microbes, and insects-particularly through shared hormonal pathways-is essential for understanding plant-pest dynamics. Such an integrative perspective not only elucidates how each organism adapts to its biotic environment but also illuminates the evolutionary origins of the regulatory molecules that underpin these interactions. Bioactive compounds are fundamental determinants of organismal traits, including growth, metamorphosis, and reproduction. In insects, developmental regulation depends on an interplay of endocrine hormones (e.g., brain hormone and juvenile hormone) and exocrine signals such as pheromones. Accordingly, juvenile hormone and its antagonists (e.g., precocenes) serve as valuable biomarkers for manipulating insect development. Complementarily, plant-derived insecticidal compounds-including pyrethrins, their synthetic analogs (pyrethroids), and antinutritional factors-provide effective means of disrupting insect growth and reproduction. Plants exhibit a comparable chemical complexity. Their development is governed by canonical phytohormones-auxins, gibberellins, cytokinins (CKs), brassinosteroids, ethylene, and abscisic acid-while biotic attack triggers the additional production of defense-specific antimicrobials known as phytoalexins. Critically, the signaling cascades activated by pathogens, herbivores, and mutualists do not operate in isolation; rather, they interact synergistically or antagonistically to fine-tune the plant's immune output, balancing resistance against pathogens with tolerance toward beneficial symbionts. Nevertheless, the precise dynamics of this hormonal interplay remain incompletely characterized. For example, emerging evidence indicates that CKs may act upstream of jasmonic acid biosynthesis and wound-responsive gene expression, introducing a new regulatory layer to the well-established developmental antagonism between auxins and CKs. This review synthesizes current knowledge on the biosynthesis and functional mechanisms of key growth-regulating compounds across kingdoms, with emphasis on their roles in mediating plant–insect interactions within broader ecological and evolutionary contexts.

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