ABA Signaling in Guard Cells Entails a Dynamic Protein–Protein Interaction Relay from the PYL-RCAR Family Receptors to Ion Channels

Department of Plant and Microbial Biology, University of California, Berkeley, CA 94720, USA.
Molecular Plant (Impact Factor: 6.34). 08/2012; 6(2). DOI: 10.1093/mp/sss078
Source: PubMed


Plant hormone abscisic acid (ABA) serves as an integrator of environmental stresses such as drought to trigger stomatal closure by regulating specific ion channels in guard cells. We previously reported that SLAC1, an outward anion channel required for stomatal closure, was regulated via reversible protein phosphorylation events involving ABA signaling components, including protein phosphatase 2C members and a SnRK2-type kinase (OST1). In this study, we reconstituted the ABA signaling pathway as a protein-protein interaction relay from the PYL/RCAR-type receptors, to the PP2C-SnRK2 phosphatase-kinase pairs, to the ion channel SLAC1. The ABA receptors interacted with and inhibited PP2C phosphatase activity against the SnRK2-type kinase, releasing active SnRK2 kinase to phosphorylate, and activate the SLAC1 channel, leading to reduced guard cell turgor and stomatal closure. Both yeast two-hybrid and bimolecular fluorescence complementation assays were used to verify the interactions among the components in the pathway. These biochemical assays demonstrated activity modifications of phosphatases and kinases by their interaction partners. The SLAC1 channel activity was used as an endpoint readout for the strength of the signaling pathway, depending on the presence of different combinations of signaling components. Further study using transgenic plants overexpressing one of the ABA receptors demonstrated that changing the relative level of interacting partners would change ABA sensitivity.

Download full-text


Available from: Chae Woo Lim, Nov 23, 2015
  • Source
    • "Plants respond to drought by synthesizing ABA, which has the effect of reducing transpirational water loss through the induction of stomatal closure (Geiger et al., 2011;Lee et al., 2013). The guard cell plasma membrane anion channels and outward potassium channels act as important conduits for solute efflux during stomatal closure, and the ABA activation of guard cell anion channels is essential for ABA-induced stomatal closure (Schroeder and Hedrich, 1989;Schroeder and Keller, 1992;Pei et al., 1997;Li et al., 2000;Scherzer et al., 2012;Lee et al., 2013). The production of transient cytosolic calcium signals, which are decoded by various calcium-binding proteins (DeFalco et al., 2010), forms part of the response to drought. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Thiamine is required for both plant growth and development. Here, the involvement of a thiamine thiazole synthase, THI1, has been demonstrated in both guard cell abscisic acid (ABA) signaling and the drought response in Arabidopsis thaliana. THI1 over-expressors proved to be more sensitive to ABA than the wild type with respect to both the activation of guard cell slow type anion channels and stomatal closure; this effectively reduced the rate of water loss from the plant and thereby enhanced its level of drought tolerance. A yeast two-hybrid strategy was used to screen a cDNA library from epidermal strips of leaves for THI1 regulatory factors, and identified CPK33, a Ca2+-dependent protein kinase, as interactor with THI1 in a plasma membrane-delimited manner. Loss-of-function cpk33 mutants were hypersensitive to ABA activation of slow type anion channels and ABA induced stomatal closure, while the CPK33 overexpression lines showed opposite phenotypes. CPK33 kinase activity was essential for ABA-induced stomatal closure. Consistent with their contrasting regulatory role over stomatal closure, THI1 suppressed CPK33 kinase activity in vitro. Together, our data reveal a novel regulatory role of thiamine thiazole synthase to kinase activity in guard cell signaling.
    Preview · Article · Dec 2015 · Plant physiology
    • "The stomatal aperture bioassay was conducted as described previously, but with some modifications (Lee et al. 2013). Briefly, leaf peels were collected from the rosette leaves of 5-week-old plants and were floated in a stomatal opening solution (SOS; 50 mM KCl, 10 mM MES-KOH, 10 μM CaCl 2 , pH 6.15) under light. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Stomata are natural pores of plants and constitute the entry points for water during transpiration. However, they also facilitate the ingress of potentially harmful bacterial pathogens. The phytohormone abscisic acid (ABA) plays a pivotal role in protecting plants against biotic stress, by regulating stomatal closure. In the present study, we investigated the mechanism whereby ABA influences plant defense responses to Pseudomonas syringae pv. tomato (Pst) DC3000, which is a virulent bacterial pathogen of Arabidopsis, at the pre-invasive stage. We found that overexpression of two ABA receptors, namely, RCAR4/PYL10-OX and RCAR5/PYL11-OX (hereafter referred to as RCARs), resulted in ABA-hypersensitive phenotypes being exhibited during the seed germination and seedling growth stages. Sensitivity to ABA enhanced the resistance of RCAR4-OX and RCAR5-OX plants to Pst DC3000, through promoting stomatal closure leading to the development of resistance to this bacterial pathogen. Protein phosphatase HAB1 is an important component that is responsible for ABA signaling and which interacts with ABA receptors. We found that hab1 mutants exhibited enhanced resistance to Pst DC3000; moreover, similar to RCAR4-OX and RCAR5-OX plants, this enhanced resistance was correlated with stomatal closure. Taken together, our findings demonstrate that alteration of RCAR4- or RCAR5-HAB1 mediated ABA signaling influences resistance to bacterial pathogens via stomatal regulation.
    No preview · Article · May 2015 · Plant Molecular Biology
  • Source
    • "Ten leaves were detached from each plant and placed in petridishes , and the loss of fresh weight was determined at the indicated times. Stomatal aperture bioassay was carried out as described before with the following modifications (Lee et al., 2013). In briefly, four rosette leaves of 4-week-old plants were detached and floated in stomatal opening solution (SOS: 50 mM KCl and 10 mM MES-KOH, pH 6.15, 10 µM CaCl 2 ) in the light. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Plants are frequently exposed to numerous environmental stresses such as dehydration and high salinity, and have developed elaborate mechanisms to counteract the deleterious effects of stress. The phytohormone abscisic acid (ABA) plays a critical role as an integrator of plant responses to water-limited condition to activate ABA signal transduction pathway. Although perception of ABA has been suggested to be important, the function of each ABA receptor remains elusive in dehydration condition. Here, we show that ABA receptor, pyrabactin resistance-like protein 8 (PYL8), functions in dehydration conditions. Transgenic plants overexpressing PYL8 exhibited hypersensitive phenotype to ABA in seed germination, seedling growth and establishment. We found that hypersensitivity to ABA of transgenic plants results in high degrees of stomatal closure in response to ABA leading to low transpiration rates and ultimately more vulnerable to drought than the wild-type plants. In addition, high expression of ABA maker genes also contributes to altered drought tolerance phenotype. Overall, this work emphasizes the importance of ABA signaling by ABA receptor in stomata during defense response to drought stress.
    Full-text · Article · Dec 2013 · The plant pathology journal
Show more