The RAB GTPase RABA1E regulates stomatal movement and drought stress response in Arabidopsis

Plant growth and development are severely affected by drought in the external environment. The phytohormone abscisic acid (ABA) is involved in cellular signaling to regulate stomatal movement in response to drought. Here, we show that RAB GTPASE HOMOLOG A1E (RABA1E) is regulated by ABA signaling and is abundantly expressed in guard cells. We report that raba1e loss-of-function mutants are more sensitive to ABA than the Col-0, whereas RABA1E overexpression lines show the opposite phenotype. RABA1E plays a negative regulatory role in ABA-mediated stomatal movement. Specifically, we found that BPL2 (BPA1 (binding protein of ACD11)-like protein), a protein targeted by RABA1E, positively regulates ABA-mediated stomatal movement by maintaining ROS homeostasis and stabilizing Ca²⁺ flow. RABA1E promotes the degradation of BPL2 through the multivesicular body pathway. Taken together, RABA1E plays a crucial role in stomatal movement and drought stress tolerance by regulating BPL2 protein levels, specifically by facilitating the vesicular transport and subsequent vesicular degradation of BPL2.