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Identification of Open Stomata1-Interacting Proteins Reveals Interactions with Sucrose Non-fermenting1-Related
Rainer Waadt1, Bianca Manalansan1, Navin Rauniyar1
1Division of Biological Sciences, Cell and Developmental Biology Section, and Center for Food and Fuel for the 21st Century, University of California, San Diego, La Jolla, California 92093-0116 (R.W., B.M., S.M., B.B., H.-H.K., J.I.S.);Centre for Organismal Studies, Plant Developmental Biology, University of Heidelberg, 69120 Heidelberg, Germany (R.W., K.S.);Department of Chemical Physiology, The Scripps Research Institute, La Jolla, California 92037 (N.R., J.R.Y.);Division of Agricultural and Life Science, Graduate School of Environmental and Life Science, Okayama University, Okayama 7008530, Japan (S.M.);Department of Molecular Biology, Cell Biology, and Biochemistry, Brown University, Providence, Rhode Island 02912 (M.A.B., A.D.);Department of Biology, Donald Danforth Plant Science Center, St. Louis, Missouri 63132 (D.A.N.); andMolecular and Computational Biology Section, University of Southern California, Los Angeles, California 90089 (S.A.K.).
Abstract:
The plant hormone abscisic acid (ABA) controls growth and development and regulates plant water status through an established signaling pathway. In the presence of ABA, pyrabactin resistance/regulatory component of ABA receptor proteins inhibit type 2C protein phosphatases (PP2Cs). This, in turn, enables the activation of Sucrose Nonfermenting1-Related Protein Kinases2 (SnRK2). Open Stomata1 (OST1)/SnRK2.6/SRK2E is a major SnRK2-type protein kinase responsible for mediating ABA responses. Arabidopsis (Arabidopsis thaliana) expressing an epitope-tagged OST1 in the recessive ost1-3 mutant background was used for the copurification and identification of OST1-interacting proteins after osmotic stress and ABA treatments. These analyses, which were confirmed using bimolecular fluorescence complementation and coimmunoprecipitation, unexpectedly revealed homo- and heteromerization of OST1 with SnRK2.2, SnRK2.3, OST1, and SnRK2.8. Furthermore, several OST1-complexed proteins were identified as type 2A protein phosphatase (PP2A) subunits and as proteins involved in lipid and galactolipid metabolism. More detailed analyses suggested an interaction network between ABA-activated SnRK2-type protein kinases and several PP2A-type protein phosphatase regulatory subunits. pp2a double mutants exhibited a reduced sensitivity to ABA during seed germination and stomatal closure and an enhanced ABA sensitivity in root growth regulation. These analyses add PP2A-type protein phosphatases as another class of protein phosphatases to the interaction network of SnRK2-type protein kinases.
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