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Sci. Signal., 9 April 2013
Vol. 6, Issue 270, p. rs8
[DOI: 10.1126/scisignal.2003509]


Genetics and Phosphoproteomics Reveal a Protein Phosphorylation Network in the Abscisic Acid Signaling Pathway in Arabidopsis thaliana

Taishi Umezawa1*, Naoyuki Sugiyama2,3, Fuminori Takahashi4, Jeffrey C. Anderson5, Yasushi Ishihama2,3, Scott C. Peck5, and Kazuo Shinozaki4*

1 Faculty of Agriculture and Graduate School of Bio-Applications and Systems Engineering, Tokyo University of Agriculture and Technology, 2-24-16 Naka-cho, Koganei, Tokyo 184-8588, Japan.
2 Institute for Advanced Biosciences, Keio University, Tsuruoka, Yamagata 997-0017, Japan.
3 Graduate School of Pharmaceutical Sciences, Kyoto University, Sakyo-ku, Kyoto 606-8501, Japan.
4 Gene Discovery Research Group, RIKEN Center for Sustainable Resource Science, 3-1-1 Kouyadai, Tsukuba, Ibaraki 305-0074, Japan.
5 Department of Biochemistry and Bond Life Sciences Center, University of Missouri, Columbia, MO 65211, USA.

Abstract: Abscisic acid (ABA) is a phytohormone that regulates diverse plant processes, including seed germination and the response to dehydration. In Arabidopsis thaliana, protein kinases of the SNF1-related protein kinase 2 (SnRK2) family are believed to transmit ABA- or dehydration-induced signals through phosphorylation of downstream substrates. By mass spectrometry, we identified proteins that were phosphorylated in Arabidopsis wild-type plants, but not in mutants lacking all three members of the SnRK2 family (srk2dei), treated with ABA or subjected to dehydration stress. The number of differentially phosphorylated peptides was greater in srk2dei plants treated with ABA than in the ones subjected to dehydration, suggesting that SnRK2 was mainly involved in ABA signaling rather than dehydration. We identified 35 peptides that were differentially phosphorylated in wild-type but not in srk2dei plants treated with ABA. Biochemical and genetic studies of candidate SnRK2-regulated phosphoproteins showed that SnRK2 promoted the ABA-induced activation of the mitogen-activated protein kinases AtMPK1 and AtMPK2; that SnRK2 mediated phosphorylation of Ser45 in a bZIP transcription factor, AREB1 (ABA-responsive element binding protein 1), and stimulated ABA-responsive gene expression; and that a previously unknown protein, SnRK2-substrate 1 (SNS1), was phosphorylated in vivo by ABA-activated SnRK2s. Reverse genetic analysis revealed that SNS1 inhibited ABA responses in Arabidopsis. Thus, by integrating genetics with phosphoproteomics, we identified multiple components of the ABA-responsive protein phosphorylation network.

* Corresponding author. E-mail: taishi{at} (T.U.); kazuo.shinozaki{at} (K.S.)

Citation: T. Umezawa, N. Sugiyama, F. Takahashi, J. C. Anderson, Y. Ishihama, S. C. Peck, K. Shinozaki, Genetics and Phosphoproteomics Reveal a Protein Phosphorylation Network in the Abscisic Acid Signaling Pathway in Arabidopsis thaliana. Sci. Signal. 6, rs8 (2013).

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