Systemic induction of an Arabidopsis plant defensin gene promoter by tobacco mosaic virus and jasmonic acid in transgenic tobacco

Abstract

The PDF1.2 gene of Arabidopsis thaliana encodes a plant defensin that is systemically induced by a SA-independent signaling pathway. Traditionally tobacco has been used to analyse pathogen-induced systemic responses. To determine whether a similar systemic signaling pathway exists in tobacco the promoter region of the PDF1.2 gene was fused to the uidA reporter gene encoding β-glucuronidase (GUS) and introduced into tobacco (cv. Xanthi-nc NN). The transgenic tobacco plants showed no increase in GUS activity after treatment with salicylate but treatment of seedlings and mature leaves with jasmonic acid, methyl viologen and rose bengal led to an induction of GUS activity with jasmonic acid being the strongest inducer. Exposure of mature transgenic plants to ethylene also led to a significant induction of GUS. Wounding resulted in highly localised induction at wound sites. Inoculation of leaves with the compatible pathogens Phytophthora parasitica var . nicotianae, Cercospora nicotianae and the incompatible tobacco mosaic virus (TMV) all led to strong GUS induction. The systemic signaling of the PDF1.2 promoter was investigated by either inoculation of a lower leaf with TMV or treatment of this leaf with jasmonic acid. Increased GUS activity was observed in the non-inoculated upper leaves at 4–6 days after treatment. Treatment of the plants with TMV induced GUS mRNA and PR1a mRNA locally and systemically while jasmonic acid treatment induced GUS mRNA only. These results are consistent with the existence of a pathogen-induced, salicylate-independent systemic signaling pathway, possibly involving ethylene and jasmonate signaling components, in both tobacco and Arabidopsis.