Salivary effector SfPDI modulates plant defense responses to enhance foraging efficiency of Spodoptera frugiperda.

Research on the interactions between herbivorous insects and plants, facilitated by insect secretions, has increasingly emphasized species with chewing mandibles over time. However, the molecular mechanisms underlying the interaction between Spodoptera frugiperda and plants remain poorly understood. In this study, we identified a protein disulfide isomerase (SfPDI) from the salivary glands of S. frugiperda that regulates the interaction between S. frugiperda and plants. We found that SfPDI is highly expressed in the salivary glands of S. frugiperda and is secreted into plants as a secretory protein. The RNAi revealed that SfPDI contributes to the growth and development of S. frugiperda on host plants, while its overexpression in tobacco induces necrosis in tobacco leaves and triggers a burst of reactive oxygen species (ROS). Differentially expressed genes suggested that SfPDI may suppresses the expression of plant JA by positively regulating MYC2 and TIFYs and negatively regulating WRKYs. Notably, SfPDI may modulate these high expression of receptors (NB-LRR, GL-RLK, and RLK) lead to hypersensitive response (HR) cell death and the accumulation of lignification of plant. This study provides a foundation for further exploring insect-plant interaction mechanisms and a theoretical basis for developing insect-resistant germplasm and environmentally friendly pest control strategies.