ROP11 GTPase Negatively Regulates ABA Signaling by Protecting ABI1 Phosphatase Activity from Inhibition by the ABA Receptor RCAR1/PYL9 in Arabidopsis

Abstract

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 plant-specific 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, co-immunoprecipitation 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.

FERONIA receptor kinase pathway suppresses abscisic acid signaling in Arabidopsis by activating ABI2 phosphatase

“…Note. When this paper was under preparation, another group reported that ROP11 interacted with ABI1 and regulated ABA responses (34,35), although authors found that ABI1 interaction with ROP11 occurs when the regulatory domain of ABI1 is deleted (35). It seems likely that different cross-talk nodes are present in subcellular compartments, such as the nucleus and cytosol, where they link alternate signals to ABA.…”

The Crystal Structure of the Plant Small GTPase OsRac1 Reveals Its Mode of Binding to NADPH Oxidase

“…Recently, the activation of AtRop2 and AtRop6 by auxin has been reported to regulate the subcellular distribution of auxin transporters PIN1 and PIN2, which control PIN-mediated pattern formation and morphogenesis in leaves and roots (18 -20). AtRop10 and AtRop11 are specific negative regulators of abscisic acid responses (21,22). In addition, AtRop9 functions as a signal integrator of auxin and abscisic acid signaling and plays an important role in embryo development and lateral root formation in A. thaliana (23).…”

Signals fly when kinases meet Rho-of-plants (ROP) small G-proteins

“…The SNF1-RELATED PROTEIN KINASE TYPE 2 -phosphatase activity of ABSCISIC ACID-INSENSITIVE 2 is enhanced in the presence of the GTP-bound AtROP11 protein [21]. This interaction prevents the binding of the ABSCISIC ACID-INSENSITIVE 2 protein to its inhibitors: the abscisic acid receptor PYRABACTIN/PYRABACTIN-LIKE PROTEINs [55]. Therefore, the active AtROP11…”