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J. Biol. Chem., Vol. 282, Issue 34, 25020-25029, August 24, 2007

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Arabidopsis MAPK Phosphatase 2 (MKP2) Positively Regulates Oxidative Stress Tolerance and Inactivates the MPK3 and MPK6 MAPKs^*

From the Michael Smith Laboratories, University of British Columbia, Vancouver, British Columbia V6T 1Z4, Canada

Two closely related Arabidopsis mitogen-activated protein kinases (MAPKs), MPK3 and MPK6, are rapidly but transiently activated in plants exposed to ozone. Although the contribution of these MAPKs to control of redox stress has been examined extensively, it remains unclear whether the dual-specificity MKPs play an essential role in the regulation of these processes. To explore this question, specific knockdown of each of the five putative MKPs in Arabidopsis was performed, and the ozone sensitivity phenotype of each MKP-suppressed line was assessed. Silencing of only one previously uncharacterized MKP, designated AtMKP2, rendered the plants hypersensitive to oxidative stress. AtMKP2-suppressed plants displayed significantly prolonged MPK3 and MPK6 activation during ozone treatment, and recombinant AtMKP2 was able to dephosphorylate both phospho-MPK3 and phospho-MPK6 in vitro, providing direct evidence that AtMKP2 may target these oxidant-activated MAPKs. In addition, the in vitro phosphatase activity of AtMKP2 was enhanced by co-incubation with either recombinant MPK3 or MPK6. In AtMKP2:YFP-expressing plants, the fusion protein was localized predominantly in the nucleus, the same compartment into which ozone-activated MPK3 and MPK6 have previously been shown to be translocated. Taken together, these data suggest that AtMKP2, a novel MKP protein in Arabidopsis, acts upon MPK3 and -6, and serves as a positive regulator of the cellular response to oxidant challenge.

Received for publication, March 5, 2007 , and in revised form, June 21, 2007.

^* This work was supported through a Discovery Grant (to B. E.) from the Natural Science and Engineering Research Council of Canada, and through a University Graduate Fellowship award (to J. S. L.). 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 To whom correspondence should be addressed: Michael Smith Laboratories, 2185 East Mall, University of British Columbia, Vancouver, British Columbia V6T 1Z4, Canada. Tel.: 604-822-3451; Fax: 604-822-2114; E-mail: bee{at}interchange.ubc.ca.

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