Plant and Cell Physiology Advance Access published online on July 18, 2007
Plant and Cell Physiology, doi:10.1093/pcp/pcm093
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Protein phosphorylation and a 14-3-3 protein binding in Vicia guard cells in response to ABA
1Department of Biology, Faculty of Science, Kyushu University, Ropponmatsu, Fukuoka 810-8560, Japan
2Precursory Research for Embryonic Science and Technology (PRESTO), Japan Science and Technology Agency, Kawaguchi, Saitama 332-0012, Japan
Corresponding author: Ken-ichiro Shimazaki,Department of Biology, Faculty of Science, Kyushu University, Ropponmatsu, Fukuoka 810-8560, Japan, Tel & Fax: 81-92-726-4758, E-mail: kenrcb{at}mbox.nc.kyushu-u.ac.jp
| Abstract |
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Under drought stress, abscisic acid (ABA) promotes stomatal closure to prevent water loss. Although protein phosphorylation plays an important role in ABA signaling, little is known about these processes on biochemical levels. In this study, we searched for substrates of protein kinases in ABA signaling through the binding of a 14-3-3 protein to phosphorylated proteins using Vicia guard cell protoplasts. ABA induced binding of a 14-3-3 protein to proteins with molecular masses of 61, 43, and 39 kDa, with the most remarkable signal in a 61 kDa protein. The ABA-induced binding to the 61 kDa protein occurred only in guard cells, and reached the maximum within 3 min at 1 µM ABA. The 61 kDa protein localized in cytosol. ABA induced the binding of endogenous vf14-3-3a to the 61 kDa protein in guard cells. Autophosphorylation of ABA-activated protein kinase (AAPK), which mediates anion channel activation, and ABA-induced phosphorylation of the 61 kDa protein showed similar time courses and similar sensitivities to protein kinase inhibitor K-252a. AAPK elicits the binding of the 14-3-3 protein to the 61 kDa protein in vitro when AAPK in guard cells was activated by ABA. The phosphorylation of the 61 kDa protein by ABA was not affected by NADPH oxidase inhibitor, H2O2, W-7, or EGTA. From these results, we conclude that the 61 kDa protein may be a substrate for AAPK and that the 61 kDa is located upstream of H2O2 and Ca2+, or on Ca2+-independent signaling pathways in guard cells.
Keywords: abscisic acid (ABA) - AAPK - guard cell protoplasts - protein phosphorylation - Vicia faba - 14-3-3 protein
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