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Plant Proteomic and Molecular Pathology Laboratory.
One powerful mechanism used by plants to ward off pathogens is called "induced resistance" and is described as the systemic broad-range long-lasting resistance to a virulent (also referred to as compatible) pathogen that occurs after exposure of part of a plant to an a-virulent (also referred to as incompatible) microbe. To date two types of induced resistance have been described: systemic acquired resistance (SAR) and induce systemic resistance (ISR). SAR as been reported in many crops and is studied in detail in the model plant Arabidopsis thaliana. Salicylic acid (SA) is a mandatory metabolite for the deployment of SAR and accordingly, SAR can be induced by treatment of a plant with SA.
Deployment of SAR, whether by an avirulent pathogen or by SA, leads to the induction of so-called Pathogenesis-Related (PR) genes that have been widely studied in various plant systems. They constitute excellent markers to study disease resistance. In Arabidopsis, PR1 represents the classical marker gene used to follow local resistance as well as SAR. In contrast to SAR, the induction of ISR is independent of SA but requires intact jasmonate and ethylene response pathways. While ISR cannot be induced by treatment of a plant with jasmonates, ethylene or a combination of both compounds, it is induced by root treatment of Arabidopsis with non-pathogenic rhizobacteria such as Pseudomonas fluorescens.
Despite these differences between SAR and ISR, both require the activity of the Arabidopsis NPR1 (a.k.a. NIM1) gene since NPR1 mutants cannot mount an effective SAR and ISR and are more susceptible to normally non-virulent pathogens. In contrast, transgenic plants overexpressing NPR1 display enhanced resistance to bacterial and fungal pathogens. NPR1 encodes a protein containing ankyrin-like repeats, a motif known to mediate protein-protein interactions. Based on sequence similarity, NPR1 has been predicted to be the homolog of the mammalian transcription factor inhibitor I k -B a , a protein that functions both in the cytoplasm and inside the nucleus. Until recently, the biochemical function of NPR1 was not known.
Current Area of Research
We have recently identified one of the molecular functions of NPR1 (Després et al., 2000). By performing yeast two-hybrid screens and electrophoretic mobility shift assays, we were able to demonstrate that NPR1 differentially interacts with members of the Arabidopsis TGA family of bZIP transcription factors and that binding of the TGA factors, to the SA-response element of the Arabidopsis SAR marker gene PR1, is enhanced by NPR1. Collectively, the results suggest that the interaction of the TGA factors with NPR1 is important for the establishment of SAR and/or the activation of defense genes.
Current studies are focusing on: a) Understanding the biochemical mechanisms by which NPR1 regulates gene expression; b) Deciphering the NPR1 signal transduction pathway in Arabidopsis using biochemical and proteomic tools; c) Applying the knowledge generated in the basic research program to engineer disease resistance in grapevine (Vitis vinifera).
Després, C., DeLong, C., Glaze, S., Liu, E., and Fobert, P.R. (2000). The Arabidopsis NPR1/NIM1 enhances the DNA binding activity of a subgroup of the TGA family of bZIP transcription factors. The Plant Cell 12, 279-290.
Desveaux, D., Després, C., Joyeux, A., Subramaniam, R., and Brisson, N. (2000). PBF-2 is a novel single-stranded DNA binding factor implicated in PR-10a gene activation in potato. The Plant Cell 12, 1477-1489.
Subramaniam, R., Després, C., and Brisson, N. (1997). A functional homolog of mammalian protein kinase C participates in the elicitor-induced defense response in potato. The Plant Cell 9, 653-664.
Després, C., Subramaniam, R., Matton, D., and Brisson, N. (1995). The activation of the potato PR10a gene requires the phosphorylation of the nuclear factor PBF-1. The Plant Cell 7, 589-598.
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