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NPR1-Independent Activation of Immediate Early Salicylic Acid-Responsive Genes in Arabidopsis

January 2004 , Volume 17 , Number  1
Pages  34 - 42

Carolina Uquillas , Ingrid Letelier , Francisca Blanco , Xavier Jordana , and Loreto Holuigue

Departamento de Genética Molecular y Microbiología, Facultad de Ciencias Biológicas, Pontificia Universidad Católica de Chile, P.O. Box 114-D, Santiago, Chile


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Accepted 30 August 2003.

Salicylic acid (SA) is a key signal for the activation of defense genes in response to stress. The activation of late defense genes by SA, such as PR-1, involves the participation of the NPR1 protein. This protein acts as coactivator of the TGA factors that recognize as-1-like elements in the PR-1 promoter. Considering that functional as-1-like elements are also found in the promoter of SA- and auxin-responsive immediate early genes, we tested the hypothesis that NPR1 is also required for activation of these genes. The expression of the immediate early genes glutathione S-transferase (GST6) and glucosyltransferase (EIGT) was studied in npr1 mutant and wild-type Arabidopsis plants. In the npr1 mutant background, SA and 2,4-dichlorophen-oxyacetic acid were unable to promote transcription of PR-1 but effectively stimulated the expression of GST6 and EIGT. Furthermore, increased binding of proteins to the GST6 as-1-like promoter element was detected in nuclear extracts from npr1 and wild-type plants after treatment with SA. In summary, these results indicate that activation of immediate early genes by SA proceeds through an NPR1-independent pathway. Therefore, we propose that activation by SA of immediate early and late genes occur by different mechanisms.



© 2004 The American Phytopathological Society