Spider mite herbivory induces an ABA-driven stomatal defense.

Arthropod herbivory poses a serious threat to crop yield, prompting plants to employ intricate defense mechanisms against pest feeding. The generalist pest 2-spotted spider mite (Tetranychus urticae) inflicts rapid damage and remains challenging due to its broad target range. In this study, we explored the Arabidopsis (Arabidopsis thaliana) response to T. urticae infestation, revealing the induction of abscisic acid (ABA), a hormone typically associated with abiotic stress adaptation, and stomatal closure during water stress. Leveraging a Forster resonance energy transfer (FRET)-based ABA biosensor (nlsABACUS2-400n), we observed elevated ABA levels in various leaf cell types postmite feeding. While ABA's role in pest resistance or susceptibility has been debated, an ABA-deficient mutant exhibited increased mite infestation alongside intact canonical biotic stress signaling, indicating an independent function of ABA in mite defense. We established that ABA-triggered stomatal closure effectively hinders mite feeding and minimizes leaf cell damage through genetic and pharmacological interventions targeting ABA levels, ABA signaling, stomatal aperture, and density. This study underscores the critical interplay between biotic and abiotic stresses in plants, highlighting how the vulnerability to mite infestation arising from open stomata, crucial for transpiration and photosynthesis, reinforces the intricate relationship between these stress types.