Impacts of insect oral secretions on defoliation-induced plant defense

- Damage caused by defoliating insect herbivores triggers induced plant defenses.
- Insect induced defense responses are amplified by Herbivore Associated Molecular Patterns (HAMPs) and Damage Associated Molecular Patterns (DAMPs).
- Effectors in insect secretions can inhibit HAMP-induced and DAMP-induced defenses.
- Established HAMPs and effectors produce species-specific reactions that partially overlap with pathogen-induced responses.
- Discovery of HAMP receptors and effector targets remains an essential challenge in the understanding of defoliator-induced defenses.

Plant responses to biotic stress involve non-self perception, signaling, and altered defense phenotypes. During attack, defoliating insects deposit gland secretions (GS) and complex foregut derived oral secretions (OS) that include GS and combined products of plant, insect, and microbial interactions. GS-derived and OS-derived biochemicals that trigger defense are termed Herbivore Associated Molecular Patterns (HAMPs) while those that promote susceptibility are termed effectors. These functions are highly context and species specific. The magnitude and direction of plant responses are orchestrated by the interaction of damage, OS/GS components, predicted receptor-ligand interactions, ion fluxes, protein kinase signaling cascades, phytohormone interactions, transcription factor activation, altered translation, and defense biosynthesis. Unlike plant-pathogen recognition, a remaining challenge is the discovery of plant receptors for defoliator-derived HAMPs.