Abscisic acid (ABA) is a central stress hormone in Arabidopsis that mediates rapid cellular responses, down- regulates cell proliferation and causes cell cycle arrest. Early signal transduction networks that down-regulate cell proliferation are of key importance for controlling mitogenesis and their mis-regulation is linked to many human diseases. The long-term goal of this research is to achieve a new and quantitative understanding of the network of events that mediate early abscisic acid signaling in the potent Arabidopsis guard cell system. We will characterize newly identified key cellular signaling mechanisms hypothesized to control the recently revealed early ABA receptor signaling core consisting of ABA receptors, PP2C protein phosphatases and SnRK2 &calcium (Ca2+)-dependent protein kinases, which mediate downstream ABA signaling.
Specific Aims : I. Regulatory proteins of eukaryotic PP2Cs and ABA receptor interactors are not well-understood. We will characterize the functions of a newly identified proposed early receptor-PP2C control loop that can counteract monomeric ABA receptor-induced ligand-free """"""""leaky"""""""" PP2C signaling. This includes the PP2C interacting and regulating ROP10 &11, ABA receptor-interacting GDP/GTP exchange factor 1 and the OST1 protein kinase. II. How the universal second messenger Ca2+ mediates specific responses in eukaryotic cells is a key question in cell signaling research and disease. Our recent results point to a """"""""Ca2+ sensitivity priming"""""""" mechanism, in which ABA primes Ca2+ sensors switching them from an inactivated Ca2+-insensitive state to a Ca2+-responsive """"""""primed"""""""" state. Priming enables a specific Ca2+ response and this novel mechanism may be used by diverse eukaryotic Ca2+-signaling pathways. We will investigate the hypothesis that the PP2Cs directly inactivate the Ca2+-dependent kinase CPK6. In addition, cross-regulation of CPK6 and the OST1 protein kinase in ABA activation of SLAC1 anion channels will be investigated. We will identify the ABA-induced Ca2+ specificity signaling mechanisms using biochemical and dynamic in vivo cell signaling analyses and via parallel functional analyses of the reconstituted multi-component ABA signalosome in Xenopus oocytes. III. In a new chemical genetics screen of 9600 compounds, we have identified a small molecule """"""""DFPM"""""""" that down-regulates ABA signaling. DFPM activates intracellular effector-triggered signaling and thereby rapidly (<3 min) deactivates ABA responses at the level of Ca2+ signaling in guard cells. New chemical genetic mutants showing strong insensitivity to DFPM-regulated ABA/Ca2+ signaling have been isolated. Selected mutants and the underlying mechanisms will be characterized to elucidate new elements and mechanisms mediating DFPM-induced rapid interference with ABA/Ca2+ signaling. This research will result in a new understanding of PP2C regulation and Ca2+ specificity signaling mechanisms, which are fundamental to numerous cell signaling processes and disease states, and will reveal novel mechanisms by which newly identified ABA receptors and regulation mechanisms control ABA signaling.

Public Health Relevance

A fundamental question in cell signaling research is how the universal second messenger Ca2+ mediates specific responses in eukaryotic cells. Furthermore, type 2C protein phosphatases (PP2Cs) play central roles in human disease, but PP2C interactors that regulate catalytic PP2C activity are largely unknown. This research project will make use of a well-developed model system to substantially advance the understanding of the mechanisms mediating specificity in Ca2+ signaling and PP2C regulation, processes that are fundamental to numerous cell signaling pathways and are misregulated in human diseases.

Agency
National Institute of Health (NIH)
Institute
National Institute of General Medical Sciences (NIGMS)
Type
Research Project (R01)
Project #
2R01GM060396-13A1
Application #
8577911
Study Section
Cellular Signaling and Regulatory Systems Study Section (CSRS)
Program Officer
Chin, Jean
Project Start
2000-02-01
Project End
2017-05-31
Budget Start
2013-07-01
Budget End
2014-05-31
Support Year
13
Fiscal Year
2013
Total Cost
$316,200
Indirect Cost
$112,200
Name
University of California San Diego
Department
Type
Other Domestic Higher Education
DUNS #
804355790
City
La Jolla
State
CA
Country
United States
Zip Code
92093
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Wang, Cun; Hu, Honghong; Qin, Xue et al. (2016) Reconstitution of CO2 Regulation of SLAC1 Anion Channel and Function of CO2-Permeable PIP2;1 Aquaporin as CARBONIC ANHYDRASE4 Interactor. Plant Cell 28:568-82
Hõrak, Hanna; Sierla, Maija; Tõldsepp, Kadri et al. (2016) A Dominant Mutation in the HT1 Kinase Uncovers Roles of MAP Kinases and GHR1 in CO2-Induced Stomatal Closure. Plant Cell 28:2493-2509
Li, Zixing; Waadt, Rainer; Schroeder, Julian I (2016) Release of GTP Exchange Factor Mediated Down-Regulation of Abscisic Acid Signal Transduction through ABA-Induced Rapid Degradation of RopGEFs. PLoS Biol 14:e1002461
Yazaki, Junshi; Galli, Mary; Kim, Alice Y et al. (2016) Mapping transcription factor interactome networks using HaloTag protein arrays. Proc Natl Acad Sci U S A 113:E4238-47
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Yamamoto, Yoshiko; Negi, Juntaro; Wang, Cun et al. (2016) The Transmembrane Region of Guard Cell SLAC1 Channels Perceives CO2 Signals via an ABA-Independent Pathway in Arabidopsis. Plant Cell 28:557-67
Aleman, Fernando; Yazaki, Junshi; Lee, Melissa et al. (2016) An ABA-increased interaction of the PYL6 ABA receptor with MYC2 Transcription Factor: A putative link of ABA and JA signaling. Sci Rep 6:28941
Kunz, Hans-Henning; Park, Jiyoung; Mevers, Emily et al. (2016) Small Molecule DFPM Derivative-Activated Plant Resistance Protein Signaling in Roots Is Unaffected by EDS1 Subcellular Targeting Signal and Chemical Genetic Isolation of victr R-Protein Mutants. PLoS One 11:e0155937
Azoulay-Shemer, Tamar; Bagheri, Andisheh; Wang, Cun et al. (2016) Starch Biosynthesis in Guard Cells But Not in Mesophyll Cells Is Involved in CO2-Induced Stomatal Closing. Plant Physiol 171:788-98

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