A salivary elicitor MsPDI3 from Mythimna separata triggers plant defense responses.

Plant immunity against herbivorous insects is often triggered by insect-derived salivary elicitors, yet the molecular mechanisms underlying their perception and signaling remain limited understood. Here, we identified a protein disulfide isomerase, MsPDI3, from the salivary glands of the oriental armyworm (Mythimna separata), which functions as an elicitor of plant defense. Transient expression of MsPDI3 in tobacco induced hypersensitive response-like necrosis and elevated salicylic acid (SA) levels. Mechanistically, MsPDI3 is secreted into maize plant through feeding, silencing MsPDI3 in larvae attenuated maize defense and enhanced larval growth, indicating its role in activating plant immunity. Using yeast two-hybrid screening and bimolecular fluorescence complementation, we demonstrated that MsPDI3 interacts with a maize Src homology 3 domain-containing protein (ZmSH3), at the plasma membrane. Virus-induced gene silencing of ZmSH3 abolished MsPDI3-triggered SA accumulation and compromised plant resistance, suggesting ZmSH3 as a key component in the defense signaling cascade. These findings established a novel link between SH3-mediated signal transduction in mediating insect-derived elicitor perception and SA-dependent defense activation, providing new insights into the molecular dialogue between plants and chewing insects.