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WRKY Transcription Factors Involved in Activation of SA Biosynthesis Genes

DOI: 10.1186/1471-2229-11-89

Keywords: WRKY28, WRKY46, ICS1, PBS3, salicylic acid, plant defense, signal transduction, transcription factors

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Abstract:

Expression studies with ICS1 promoter::β-glucuronidase (GUS) genes in Arabidopsis thaliana protoplasts cotransfected with 35S::WRKY28 showed that over expression of WRKY28 resulted in a strong increase in GUS expression. Moreover, qRT-PCR analyses indicated that the endogenous ICS1 and PBS3 genes were highly expressed in protoplasts overexpressing WRKY28 or WRKY46, respectively. Electrophoretic mobility shift assays indentified potential WRKY28 binding sites in the ICS1 promoter, positioned -445 and -460 base pairs upstream of the transcription start site. Mutation of these sites in protoplast transactivation assays showed that these binding sites are functionally important for activation of the ICS1 promoter. Chromatin immunoprecipitation assays with haemagglutinin-epitope-tagged WRKY28 showed that the region of the ICS1 promoter containing the binding sites at -445 and -460 was highly enriched in the immunoprecipitated DNA.The results obtained here confirm results from our multiple microarray co-expression analyses indicating that WRKY28 and WRKY46 are transcriptional activators of ICS1 and PBS3, respectively, and support this in silico screening as a powerful tool for identifying new components of stress signaling pathways.Because of their sessile nature, plants have evolved very sophisticated mechanisms to actively cope with different sorts of stresses. The various defense mechanisms are controlled by signaling molecules like salicylic acid (SA), jasmonic acid (JA), and ethylene, or by combinations of these signal compounds. SA accumulates locally in infected leaves, as well as in non-infected systemic leaves after infection with biotrophic pathogens and mediates the induced expression of defense genes, resulting in an enhanced state of defense known as systemic acquired resistance (SAR) [1-5]. SAR is a long-lasting broad-spectrum resistance against a variety of pathogenic fungi, bacteria and viruses [6,7]. Also exogenous application of SA results in induced exp

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