Stomata, a vulnerability in the plant defence against phytophagous mites that ABA can overcome

Abstract Arthropod herbivory possess a significant threat to crop yield, prompting plants to employ intricate defense mechanisms against pest feeding. The generalist pest, Tetranychus urticae , inflicts rapid damage and remains a challenge due to its broad target range. In this study, we explored Arabidopsis thaliana’s response to T. urticae infestation, revealing the induction of abscisic acid (ABA), a hormone typically associated with abiotic stress adaptation, including stomatal closure during water stress. Leveraging a FRET-based ABA biosensor (nlsABACUS2-400n), we observed elevated ABA levels in various leaf cell types post-mite 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 signalling, indicating an independent function of ABA in mite defense. Through genetic and pharmacological interventions targeting ABA levels, ABA signalling, stomatal aperture, and density, we established that ABA-triggered stomatal closure effectively hinders mite feeding and minimizes leaf cell damage. 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, underscores the intricate relationship between these two stress types.