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Published Online April 30, 2009
Science DOI: 10.1126/science.1173041

Reports

Submitted on October 27, 2008
Accepted on April 16, 2009

Abscisic Acid Inhibits Type 2C Protein Phosphatases via the PYR/PYL Family of START Proteins

Sang-Youl Park 1{dagger}, Pauline Fung 2{dagger}, Noriyuki Nishimura 3{ddagger}, Davin R. Jensen 4{ddagger}, Hiroaki Fujii 1, Yang Zhao 2, Shelley Lumba 2, Julia Santiago 5, Americo Rodrigues 5, Tsz-fung F. Chow 2, Simon E. Alfred 2, Dario Bonetta 6, Ruth Finkelstein 7, Nicholas J. Provart 8, Darrell Desveaux 8, Pedro L. Rodriguez 5, Peter McCourt 2, Jian-Kang Zhu 1, Julian I. Schroeder 3, Brian F. Volkman 4, Sean R. Cutler 9*

1 Department of Botany and Plant Sciences, University of California at Riverside, Riverside, CA 92521, USA.
2 Department of Cell and Systems Biology, University of Toronto, 25 Willcocks Street, Toronto, ON, M5S 3B2, Canada.
3 Division of Biological Sciences, Cell and Developmental Biology Section, University of California at San Diego, 9500 Gilman Drive, La Jolla, CA 92093, USA.
4 Department of Biochemistry, Medical College of Wisconsin, 8701 Watertown Plank Road, Milwaukee, WI 53226, USA.
5 Instituto de Biología Molecular y Celular de Plantas, Universidad Politécnica de Valencia, Avenida de los Naranjos, Edificio CPI, 8E, ES-46022 Valencia, Spain.
6 Faculty of Science, University of Ontario Institute of Technology, 2000 Simcoe Street North, Oshawa, ON, L1H 7K4, Canada.
7 Department of Molecular, Cellular and Developmental Biology, University of California at Santa Barbara, Santa Barbara, CA 93106, USA.
8 Department of Cell and Systems Biology, University of Toronto, 25 Willcocks Street, Toronto, ON, M5S 3B2, Canada.; Centre for the Analysis of Genome Evolution and Function, University of Toronto, 25 Willcocks Street, Toronto, ON, M5S 3B2, Canada.
9 Department of Botany and Plant Sciences, University of California at Riverside, Riverside, CA 92521, USA.; Center for Plant Cell Biology, University of California at Riverside, Riverside, CA 92521, USA.; Institute for Genome Biology, University of California at Riverside, Riverside, CA 92521, USA.; Department of Chemistry, University of California at Riverside, Riverside, CA 92521, USA.

* To whom correspondence should be addressed.
Sean R. Cutler , E-mail: sean.cutler{at}ucr.edu

{dagger}These authors contributed equally to this work.

{ddagger}These authors contributed equally to this work.

Type 2C protein phosphatases (PP2Cs) are vitally involved in abscisic acid (ABA) signaling. Here, we show that a synthetic growth inhibitor called pyrabactin functions as a selective ABA agonist. Pyrabactin acts through PYRABACTIN RESISTANCE 1 (PYR1), the founding member of a family of START proteins called PYR/PYLs, which are necessary for both pyrabactin and ABA signaling in vivo. We show that ABA binds to PYR1, which in turn binds to and inhibits PP2Cs. We conclude that PYR/PYLs are ABA receptors functioning at the apex of a negative regulatory pathway that controls ABA signaling by inhibiting PP2Cs. Our results illustrate the power of the chemical genetic approach for sidestepping genetic redundancy.


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