Untitled

Abstract

The plant defensin PDF1.2 has previously been shown to accumulate systemically via a salicylic acid-independent pathway in leaves of Arabidopsis upon challenge by fungal pathogens. To further investigate the signalling and transcriptional processes underlying plant defensin induction, a DNA fragment containing 1184 bp and 1232 bp upstream of the transcriptional and translational start sites, respectively, was cloned by inverse PCR. To test for promoter 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 transgenic plants had no effect on GUS activity. Treatment of the transgenic plants with either jasmonates or the active oxygen generating compound paraquat strongly induced the reporter gene. In contrast, neither salicylate nor its functional analogues 2,6-dichloroisonicotinic acid and 1,2,3-benzothiodiazole-7-carbothioic acid S-methyl ester resulted in reporter gene induction. These results are consistent with the existence of a salicylic acid-independent signalling pathway, possibly involving jasmonates as regulators, that 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 signalling pathway.

TINY, a Dehydration-responsive Element (DRE)-binding Protein-like Transcription Factor Connecting the DRE- and Ethylene-responsive Element-mediated Signaling Pathways in Arabidopsis

“…Because TINY was able to bind to both DRE and ERE elements and activate the downstream genes, its response to various stimuli indicated that TINY might participate in both DRE-and ERE-mediated signaling pathways. Here, the transgenic Arabidopsis plants overexpressing TINY did showed elevated expression levels of not only DRE containing genes, such as COR6.6, COR15A, and COR78 (37,38) in non-stressed conditions, but also some ERE containing genes, including PDF1.2 (39) and HLS1 (26), were directly activated in transgenic lines without ethylene treatment (Fig. 6), evidence that gives strong support to the hypothesis mentioned above.…”

“…As was shown in Fig. 6B, the expression levels of both the DREdriven genes, COR6.6, COR15A, and COR78 (37,38), and the ERE-driven genes, PDF1.2 (39) and HLS1 (26), were elevated under non-stressed conditions in TINY1 and TINY7 when compared with those in the control plants. Moreover, the expression levels of these genes were correlated with that of TINY, which strongly suggested that TINY could activate both the DRE-and the ERE-driven genes in vivo.…”

The expression pattern of the Picea glauca Defensin 1 promoter is maintained in Arabidopsis thaliana, indicating the conservation of signalling pathways between angiosperms and gymnosperms*

“…A motif involved in the SA response was also found in our promoter, although it was located very near the 3'-end of the promoter between the TATA box and the ATG, and in eight out of the 14 Arabidopsis promoters. It is well established that, in contrast to most pathogen-induced genes, defensin induction, namely PDF1.2, is independent of the SA pathway (Manners et al , 1998). …”

“…For these reasons, enhanced disease resistance following defensin over-expression has been reported in potatoes, tomatoes, carrots, wheat, tobacco, melon, rice, Norway spruce, pine, and Arabidopsis (Terras et al , 1995; Wang et al , 1999; Gao et al , 2000; Parashina et al , 2000; Elfstrand et al , 2001; Kim et al , 2004; Choi et al , 2009; Ntui et al , 2010; Portieles et al , 2010; Li et al , 2011); this list may not be exhaustive. Plant defensin expression in various organs and treatments has been well studied in Arabidopsis (Kragh et al , 1995; Terras et al , 1995; Manners et al , 1998; Thomma and Broekaert, 1998). Manners et al (1998) demonstrated that PDF1.2 was highly responsive to JA but insensitive to SA; hence, PDF1.2 is now frequently used as a marker for the ethylene/jasmonate-mediated signalling pathway.…”

“…In Arabidopsis thaliana , for instance, 14 different defensins have been described. One of the most well-studied defensins, PDF1.2 (plant defensin 1.2) , is induced by methyl jasmonate (MeJa) and fungal pathogens but is not induced by salicylic acid (SA) (Manners et al , 1998). Other members of the same family, namely PDF1.1 , PDF2.1 , PDF2.2 , and PDF2.3 , are constitutively expressed (Thomma et al , 2002).…”