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| Mechanisms in Pathogen Defense and their Relation with other Stress Responses |
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Karl-Heinz Kogel, Ulrich Beckhove, Katrin Beßer, Ralph Hückelhoven and Gregor Langen
Institut für Phytopathologie und Angewandte Zoologie (IPAZ), Justus-Liebig-Universität, Heinrich-Buff-Ring 26-32, D-35392 Giessen, Germany
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A detailed molecular analysis of the phenomenon of Induced Disease Resistance in barley to biotrophic fungi revealed a cross-talk between components of salicylate-based and the octadecanoid pathway. Salicylic acid (SA) and its synthetic mimics 2,6-dichloroisonicotinic acid (DCINA) and benzo(1,2,3)thiadiazole-7-carbothioic acid S-methyl ester (BTH) protect barley systemically against powdery mildew (Blumeria graminis fsp. hordei Bgh) infection by strengthening plant defence mechanisms that result in H202 burst, effective papillae and host cell death (Hückelhoven et al. 1999 and 2000; Kogel and Hückelhoven 1999). Concomitantly, we observed differential expression of a number of barley chemically induced (BCI) genes encoding a lipoxygenase (BCI-1), a thionin (BCI-2), an acid phosphatase (BCI-3), a Ca2+-binding EF-hand protein (BCI-4), a serine proteinase inhibitor (BCI-7), a fatty acid desaturase (BCI-8) and several further proteins with as yet unknown function (Beßer et al. 2000). Homologues of four BCI genes were detected in wheat and were also differentially regulated upon chemical activation of disease resistance. Except BCI-4 and BCI-5 (unknown function) the genes were also induced by exogenous application of jasmonates whereas treatments that raise endogenous jasmonates (like osmotic stress) as well as wounding were less effective (Hause et al. 1999). Analysis of BCI gene function in transient transformation assays using barley leaf segments indicated involvement of these genes in controlling penetration resistance of barley to powdery mildew fungus.
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- Hückelhoven R, Fodor J Trujillo M, Kogel KH (2000) Barley resistance gene- and Rar-mutants not expressing the hypersensitive cell death response against Blumeria graminis f.sp. hordei are modified in their ability to accumulate reactive oxygen intermediates at interaction sites. Planta 212, 16-24.
- Kogel KH, Hückelhoven R, (1999) Superoxide generation in chemically activated resistance of barley in response to inoculation with the powdery milldew fungus. J Phytopathology 147, 1-4
- Hückelhoven R, Fodor J, Preis C, Kogel KH (1999) Hypersensitive Cell Death and Papilla Formation in Barley Attacked by the Powdery Mildew Fungus are Associated with H2O2 Accumulation but are not Accompanied by enhanced Concentrations of Salicylic Acid. Plant Physiology 119, 1251-1260
- Hause B, Vörös K. Kogel KH, Beßer K, Wasternack C (1999) A jasmonate-responsive lipoxygenase of barley leaves is induced by plant activators but not by pathogens. J Plant Physiology 154, 459-462
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