First published online June 9, 2006; 10.1105/tpc.105.039677
The Plant Cell 18:1750-1765 (2006)
© 2006 American Society of Plant Biologists
OPEN ACCESS ARTICLE
A Comprehensive StructureFunction Analysis of Arabidopsis SNI1 Defines Essential Regions and Transcriptional Repressor Activity[W],[OA]
Rebecca A. Mosher1,
Wendy E. Durrant,
Dong Wang,
Junqi Song and
Xinnian Dong2
Developmental, Cell, and Molecular Biology Group, Department of Biology, Duke University, Durham, North Carolina 27708
2 To whom correspondence should be addressed. E-mail xdong{at}duke.edu; fax 919-613-8177.
The expression of systemic acquired resistance (SAR) in plants involves the upregulation of many Pathogenesis-Related (PR) genes, which work in concert to confer resistance to a broad spectrum of pathogens. Because SAR is a costly process, SAR-associated transcription must be tightly regulated. Arabidopsis thaliana SNI1 (for Suppressor of NPR1, Inducible) is a negative regulator of SAR required to dampen the basal expression of PR genes. Whole genome transcriptional profiling showed that in the sni1 mutant, Nonexpresser of PR genes (NPR1)dependent benzothiadiazole S-methylesterresponsive genes were specifically derepressed. Interestingly, SNI1 also repressed transcription when expressed in yeast, suggesting that it functions as an active transcriptional repressor through a highly conserved mechanism. Chromatin immunoprecipitation indicated that histone modification may be involved in SNI1-mediated repression. Sequence comparison with orthologs in other plant species and a saturating NAAIRS-scanning mutagenesis of SNI1 identified regions in SNI1 that are required for its activity. The structural similarity of SNI1 to Armadillo repeat proteins implies that SNI1 may form a scaffold for interaction with proteins that modulate transcription.
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