Insect Oral Secretion Protein and Its Related Core Peptide Induce the Host Plant’s Endogenous Abscisic Acid to Enhance Resistance against Insect

Plants perceive proteins from insect-derived oral secretion (OS) and regulate the classical endogenous hormone jasmonic acid to resist insects, but the role of abscisic acid (ABA) in this process is poorly understood. In this study, we used the specialist herbivorous caterpillar Plutella xylostella and cruciferous plants as a model to investigate how the ABA hormone responds to the OS and its core peptide from the insect. Through proteomics and Western blotting analysis, glucosinolate sulfatase 1 (GSS1) was identified in OS. Yeast library screening revealed that GSS1 and its 28-amino-acid core peptide (GSS1-P1) interact with ABA biosynthetic enzyme ABA1. Arabidopsis overexpressing GSS1 and plants treated with synthetic GSS1-P1 showed elevated ABA levels. Transcriptome analysis and RT-qPCR confirmed that GSS1-P1 upregulates WRKY18 and ABA1 expression, modulating ABA production. Both GSS1-P1 application and optimal ABA concentrations enhanced plant resistance to herbivory. Our study shows that GSS1 and its peptide stimulate ABA production, boosting plant–insect resistance and highlighting ABA’s potential role in pest-stress response.