Plant Cell Advance Online Publication
Published on December 15, 2006; 10.1105/tpc.106.046953
Received August 29, 2006
Returned for revision October 20, 2006
Accepted November 6, 2006
The Coactivator Function of Arabidopsis NPR1 Requires the Core of Its BTB/POZ Domain and the Oxidation of C-Terminal Cysteines
Amanda Rochon 1, Patrick Boyle 1, Tracy Wignes 2, Pierre R. Fobert 2, and Charles Després 1*
1 Department of Biological Sciences, Brock University, St. Catharines, Ontario, Canada L2S 3A1
2 National Research Council Canada, Plant Biotechnology Institute, Saskatoon, Saskatchewan, Canada S7N 0W9
* To whom correspondence should be addressed. E-mail: cdespres{at}brocku.ca.
NONEXPRESSOR OF PATHOGENESIS-RELATED GENES1 (NPR1) regulates systemic acquired resistance (SAR) in Arabidopsis thaliana, and current models propose that after treatment with salicylic acid (SA), Cys-82 and Cys-216 of NPR1 are reduced, leading to nuclear import. The interaction of nucleus-localized NPR1 with TGA transcription factors results in the activation of defense genes, including the SAR marker PATHOGENESIS-RELATED-1 (PR-1), and the deployment of SAR. Little is known about how TGA factors or NPR1 regulate transcription or whether a TGA-NPR1 complex forms on DNA. We show that TGA2 and NPR1 are recruited to PR-1 independently of each other and of SA treatment. Consistent with the result that a triple knockout in TGA2/5/6 derepresses PR-1, in vivo plant transcription assays revealed that TGA2 is not an autonomous transcription activator but is a transcriptional repressor in both untreated and SA-treated cells. However, after stimulation with SA, TGA2 is incorporated into a transactivating complex with NPR1, forming an enhanceosome that requires the core of the NPR1 BTB/POZ domain (residues 80 to 91) and the oxidation of NPR1 Cys-521 and Cys-529. These Cys residues are found in a new type of transactivation domain that we term Cys-oxidized. These data further our understanding of the mechanism by which TGA2 and NPR1 activate Arabidopsis PR-1.
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