SYSTEMIC INDUCTION OF AN ARABIDOPSIS PLANT DEFENSIN GENE PROMOTER BY TOBACCO MOSAIC-VIRUS AND JASMONIC ACID IN TRANSGENIC TOBACCO

The PDF1.2 gene of Arabidopsis thaliana encodes a plant defensin that is systemically induced by a SA-independent signaling pathway. Traditi onally tobacco has been used to analyse pathogen-induced systemic resp onses. To determine whether a similar systemic signaling pathway exist s in tobacco the promoter region of the PDF1.2 gene was fused to the u idA reporter gene encoding beta-glucuronidase (GUS) and introduced int o 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 an d rose bengal led to an induction of GUS activity with jasmonic acid b eing the strongest inducer. Exposure of mature transgenic plants to et hylene also led to a significant induction of GUS. Wounding resulted i n highly localised induction at wound sites. Inoculation of leaves wit h the compatible pathogens Phytophthora parasitica var, nicotianae, Ce rcospora nicotianae and the incompatible tobacco mosaic virus (TMV) al l led to strong GUS induction. The systemic signaling of the PDF1.2 pr omoter 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 trea tment. Treatment of the plants with TMV induced GUS mRNA and PR1a mRNA locally and systemically while jasmonic acid treatment induced GUS mR NA 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. (C) 1998 Elsevier Science Ireland Ltd. All rights re served.