Molecular defenses: Unraveling plant resistance mechanisms against insect herbivory

Abstract

As immobile organisms, plants are persistently exposed to a wide array of biotic and abiotic stressors throughout their life cycle. Among biotic challenges, insect herbivory poses a significant threat, contributing to the loss of approximately 20% of global agricultural productivity each year. Insect herbivores display a broad spectrum of feeding strategies, including leaf defoliation, sap-sucking, and phloem-feeding each triggering distinct and often complex defensive responses in plants. These interactions have driven the evolution of sophisticated plant defense mechanisms over millions of years. Herbivore associated elicitors (HAE) are molecules produced by herbivore as Oral secretions. A key aspect of plant defense involves the recognition of herbivore attack through conserved molecules, termed herbivore-associated molecular patterns (HAMPs) and damage-associated molecular patterns (DAMPs). These molecules are detected by plant pattern recognition receptors (PRRs), which activate PRR-triggered immunity (PTI), a defense pathway analogous to pathogen-associated molecular pattern (PAMP)-triggered immunity. The recent discovery of DAMP receptors has provided new insights into the distinct and overlapping roles of DAMPs and HAMPs in mediating plant-herbivore interactions. Despite advances in understanding pathogen-induced responses, a unified conceptual framework, such as the zigzag model established for plant-pathogen interactions, is lacking for plant-insect systems. This review consolidates current insights into insect herbivore classification, plant perception of herbivory, and the spatial and temporal dynamics of induced plant defenses. It further underscores the need for a comprehensive model to elucidate the molecular underpinnings of plant-insect interactions and guide future research in plant defense biology.