The phytohormone abscisic acid (ABA) regulates many key processes in plants,such as seed germination,seedling growth,and abiotic stress tolerance.In recent years,a minimal set of core components of a major ABA signaling pathway has been discovered.These components include a RCAR/PYR/PYL family of ABA receptors,a group of PP2C phosphatases,and three SnRK2 kinases.However,how the interactions between the receptors and their targets are regulated by other proteins remains largely unknown.In a companion paper published in this issue,we showed that ROP11,a member of the plantspecific Rho-like small GTPase family,negatively regulates multiple ABA responses in Arabidopsis.The current work demonstrated that the constitutively active ROP11 (CA-ROP11) can modulate the RCAR1/PYL9-mediated ABA signaling pathway based on reconstitution assays in Arabidopsis thaliana protoplasts.Furthermore,using luciferase complementation imaging,yeast two-hybrid assays,coimmunoprecipitation assays in Nicotiana benthamiana and bimolecular fluorescence complementation assays,we demonstrated that CA-ROP11 directly interacts with ABI1,a signaling component downstream of RCAR1/PYL9.Finally,we provided biochemical evidence that CA-ROP11 protects ABI1 phosphatase activity from inhibition by RCAR1/PYL9 and thus negatively regulates ABA signaling in plant cells.A model of how ROP11 acts to negatively regulate ABA signaling is presented.