The promoter of the plant defensin gene PDF1.2 from Arabidopsis is systemically activated by fungal pathogens and responds to methyl jasmonate but not to salicylic acid

The plant defensin PDF1.2 has previously been shown to accumulate systemica lly via a salicylic acid-independent pathway in leaves of Arabidopsis upon challenge by fungal pathogens. To further investigate the signalling and tr anscriptional processes underlying plant defensin induction, a DNA fragment containing 1184 bp and 1232 bp upstream of the transcriptional and transla tional start sites, respectively, was cloned by inverse PCR. To test for pr omoter activity this DNA fragment was linked to the beta-glucuronidase (GUS )-encoding region of the UidA gene as a translational fusion and introduced into Arabidopsis ecotype C-24. Challenge of the transgenic plants with the fungal pathogens Alternaria brassicicola and Botrytis cinerea resulted in both local and systemic induction of the reporter gene. Wounding of the tra nsgenic plants had no effect on GUS activity. Treatment of the transgenic p lants with either jasmonates or the active oxygen generating compound paraq uat strongly induced the reporter gene. In contrast, neither salicylate nor its functional analogues 2,6-dichloroisonicotinic acid and 1,2,3-benzothio diazole-7-carbothioic acid S-methyl ester resulted in reporter gene inducti on. These results are consistent with the existence of a salicylic acid-ind ependent signalling pathway, possibly involving jasmonates as regulators, t hat is triggered by pathogen challenge but not by wounding. The transgenic plants containing the PDF1.2-based promoter-reporter construct will provide useful tools for future genetic dissection of this novel systemic signalli ng pathway.