Journal of Biological Chemistry
Volume 282, Issue 3, 19 January 2007, Pages 1916-1924
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Mechanisms of Signal Transduction
The ATP Binding Cassette Transporter AtMRP5 Modulates Anion and Calcium Channel Activities in Arabidopsis Guard Cells*

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Stomatal guard cells control CO2 uptake and water loss between plants and the atmosphere. Stomatal closure in response to the drought stress hormone, abscisic acid (ABA), results from anion and K+ release from guard cells. Previous studies have shown that cytosolic Ca2+ elevation and ABA activate S-type anion channels in the plasma membrane of guard cells, leading to stomatal closure. However, membrane-bound regulators of abscisic acid signaling and guard cell anion channels remain unknown. Here we show that the ATP binding cassette (ABC) protein AtMRP5 is localized to the plasma membrane. Mutation in the AtMRP5 ABC protein impairs abscisic acid and cytosolic Ca2+ activation of slow (S-type) anion channels in the plasma membrane of guard cells. Interestingly, atmrp5 insertion mutant guard cells also show impairment in abscisic acid activation of Ca2+-permeable channel currents in the plasma membrane of guard cells. These data provide evidence that the AtMRP5 ABC transporter is a central regulator of guard cell ion channel during abscisic acid and Ca2+ signal transduction in guard cells.

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*

This work was supported by National Institutes of Health Grant R01GM060396 and National Science Foundation Grant MCB0417118 (to J. I. S.), by the Swiss National Foundation (Grant 3100A0-103911 to E. M.), and partly by Grant R01-2006-000-11026-0 from KOSEF (to M. H. C.). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

The on-line version of this article (available at http://www.jbc.org) contains supplemental Figs. S1 and S2.

1

These authors contributed equally to this work.

2

Present address: Dept. of Biological Sciences, Seoul National University, Seoul 151-747, Korea.

3

Present address: CEA Cadarache, UMR 163 CEA-CNRS, DEVM-LEMS, BP 1, F-13108 St. Paul Lez Durance, France.