Plant Growth-Promoting\nRhizobacteria Paenibacillus polymyxa HL14–3 Inoculation\nEnhances Drought Tolerance in Cucumber by Triggering Abscisic Acid-Mediated\nStomatal Closure

Drought\nlimits crop growth and yield. Inoculation with\nplant growth-promoting\nrhizobacteria (PGPR) emerges as a promising strategy to protect crops\nagainst drought. However, the number of drought-tolerant PGPR is limited,\nand the regulation mechanisms remain elusive. Here, we screened a\nnovel drought-tolerant PGPR strain Paenibacillus polymyxa HL14–3 with high drought-tolerance potential and efficient\ncolonization ability. P. polymyxa HL14–3\ninoculation effectively alleviated drought-induced growth inhibition\nand oxidative stress and improved the root system architecture in\ncucumber. Furthermore, P. polymyxa HL14–3\nimproved stomatal closure and leaf relative water content, reducing\nwater loss in cucumber under drought stress. Importantly, P. polymyxa HL14–3 inoculation enhanced drought\ntolerance in cucumber by inducing abscisic acid synthesis, which was\ncounteracted by root irrigation with the ABA synthesis inhibitor fluridone.\nTogether, our results demonstrate that P. polymyxa HL14–3 inoculation enhances drought tolerance in cucumber\nby triggering ABA-mediated stomatal closure, providing an effective\ndrought-tolerant PGPR for promoting agricultural production in arid\nareas.