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Originally published in Science Express on 30 April 2009
Science 22 May 2009:
Vol. 324. no. 5930, pp. 1068 - 1071
DOI: 10.1126/science.1173041
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Reports

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

Sang-Youl Park,1,* Pauline Fung,2,* Noriyuki Nishimura,4,{dagger} Davin R. Jensen,8,{dagger} 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,2,3 Darrell Desveaux,2,3 Pedro L. Rodriguez,5 Peter McCourt,2 Jian-Kang Zhu,1 Julian I. Schroeder,4 Brian F. Volkman,8 Sean R. Cutler1,9,10,11,{ddagger}

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.

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 Centre for the Analysis of Genome Evolution and Function, University of Toronto, 25 Willcocks Street, Toronto, ON, M5S 3B2, Canada.
4 Division of Biological Sciences, Cell and Developmental Biology Section, University of California at San Diego, 9500 Gilman Drive, La Jolla, CA 92093, 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 Biochemistry, Medical College of Wisconsin, 8701 Watertown Plank Road, Milwaukee, WI 53226, USA.
9 Center for Plant Cell Biology, University of California at Riverside, Riverside, CA 92521, USA.
10 Institute for Genome Biology, University of California at Riverside, Riverside, CA 92521, USA.
11 Department of Chemistry, University of California at Riverside, Riverside, CA 92521, USA.

* These authors contributed equally to the work described.

{dagger} These authors contributed equally to the work described.

{ddagger} To whom correspondence should be addressed. E-mail: sean.cutler{at}ucr.edu

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