Abstract
Plants have evolved several adaptive strategies through physiological changes in response to herbivore attacks. Plant secondary metabolites (PSMs) are synthesized to provide defensive functions and regulate defense signaling pathways to safeguard plants against herbivores. Herbivore injury initiates complex reactions which ultimately lead to synthesis and accumulation of PSMs. The biosynthesis of these metabolites is regulated by the interplay of signaling molecules comprising phytohormones. Plant volatile metabolites are released upon herbivore attack and are capable of directly inducing or priming hormonal defense signaling pathways. Secondary metabolites enable plants to quickly detect herbivore attacks and respond in a timely way in a rapidly changing scenario of pest and environment. Several studies have suggested that the potential for adaptation and/or resistance by insect herbivores to secondary metabolites is limited. These metabolites cause direct toxicity to insect pests, stimulate antixenosis mechanisms in plants to insect herbivores, and, by recruiting herbivore natural enemies, indirectly protect the plants. Herbivores adapt to secondary metabolites by the up/down regulation of sensory genes, and sequestration or detoxification of toxic metabolites. PSMs modulate multi-trophic interactions involving host plants, herbivores, natural enemies and pollinators. Although the role of secondary metabolites in plant-pollinator interplay has been little explored, several reports suggest that both plants and pollinators are mutually benefited. Molecular insights into the regulatory proteins and genes involved in the biosynthesis of secondary metabolites will pave the way for the metabolic engineering of biosynthetic pathway intermediates for improving plant tolerance to herbivores. This review throws light on the role of PSMs in modulating multi-trophic interactions, contributing to the knowledge of plant-herbivore interactions to enable their management in an eco-friendly and sustainable manner.
Highlights
All living organisms have to face environmental and biotic challenges during their lifetime
This review presents the latest updated information regarding the protective role of secondary metabolites in sustainably maintaining plant health
Secondary metabolites have become a subject of great interest because of their significant application in plant stress physiology
Summary
All living organisms have to face environmental and biotic challenges during their lifetime. The fittest organisms have the diverse genetic potential to defend themselves, or resist or avoid stress consequences which hamper their physiological functions, permitting them to grow, develop and survive. This adaptive evolution ensures the ecological specialization of a species for a specific niche [1] and results in speciation [2]. Recent genetic and chemical investigations have demonstrated the multifunctional nature of PSMs, which act as potent regulators of plant growth, defense and primary metabolism. This review provides substantial evidence that secondary metabolites derived from plants can be used to develop effective, environmentally friendly, Int. J.
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