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J. Biol. Chem., Vol. 283, Issue 14, 9269-9275, April 4, 2008

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The Transcriptional Co-activator MBF1c Is a Key Regulator of Thermotolerance in Arabidopsis thaliana^*

Nobuhiro Suzuki, Sunil Bajad, Joel Shuman, Vladimir Shulaev, and Ron Mittler^¶1

From the Department of Biochemistry and Molecular Biology, University of Nevada, MS200, Reno, Nevada 89557, Virginia Bioinformatics Institute, Virginia Tech, Blacksburg, Virginia 24061, and the ^¶Department of Plant Sciences, Hebrew University of Jerusalem, Givat Ram, Jerusalem 91904, Israel

The ability of an organism to acclimate to its environment is a key determinant in its global distribution and capacity to compete with other organisms. The heat stress response, a highly conserved environmental and developmental program in eukaryotic and prokaryotic organisms, is an important component of the acclimation response of plants. Previous studies have shown that heat shock transcription factors play an important role in thermotolerance in plants and other organisms, controlling the expression of different heat shock proteins and detoxifying enzymes. In contrast, although several other pathways, involving ethylene, salicylic acid (SA), and trehalose, were recently shown to play a central role in thermotolerance in plants, a key regulator of these responses was not identified. Here we report that the highly conserved transcriptional co-activator, MBF1c (multiprotein bridging factor 1c), is a key regulator of thermotolerance in Arabidopsis thaliana. MBF1c protein accumulates rapidly and is localized to nuclei during heat stress. MBF1c is required for thermotolerance and functions upstream to SA, trehalose, ethylene, and pathogenesis-related protein 1 during heat stress. In contrast, MBF1c is not required for the expression of transcripts encoding HSFA2 and different heat shock proteins. Interestingly, MBF1c interacts with TPS5 (trehalose phosphate synthase 5), which is also heat-inducible, and mutants deficient in TPS5 are thermosensitive. Our results provide evidence for the existence of a tightly coordinated heat stress-response network, involving trehalose-, SA-, and ethylene-signaling pathways, that is under the control of MBF1c.

Received for publication, November 8, 2007 , and in revised form, December 26, 2007.

^* This work was supported by National Science Foundation Grants IBN-0420033 and NSF-0431327, the Nevada Agricultural Experimental Station, and National Institutes of Health IDeA Network of Biomedical Research Excellence (INBRE) Grant P20 RR-016464. 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. 1-3 and Table 1.

¹ To whom correspondence should be addressed: Dept. of Biochemistry and Molecular Biology, University of Nevada, MS200, Reno, NV 89557. Tel.: 775-784-1384; Fax: 775-784-6911; E-mail: ronm{at}unr.edu.

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