Suppression of fungal β-glucan-induced plant defence in soybean (Glycine max L.) by cyclic 1,3-1,6-β-glucans from the symbiont Bradyrhizobium japonicum |
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Authors: | Axel Mithöfer Arvind A Bhagwat Markus Feger Jürgen Ebel |
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Institution: | (1) Botanisches Institut der Universität, Menzinger Strasse 67, D-80638 München, Germany;(2) Agricultural Research Service, BARC-W, USDA, 20705 Beltsville, MD, USA;(3) Department of Agronomy, University of Maryland, 20742 College Park, MD, USA |
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Abstract: | The production of antimicrobial phytoalexins is one of the best-known inducible defence responses following microbial infection of plants or treatment with elicitors. In the legume soybean (Glycine max L.), 1,3-1,6--glucans derived from the fungal pathogen Phytophthora sojae have been identified as potent elicitors of the synthesis of the phytoalexin, glyceollin. Recently it has been reported that during symbiotic interaction between soybean and the nitrogen-fixing bacterium Bradyrhizobium japonicum USDA 110 the bacteria synthesize cyclic 1,3-1,6--glucans. Here we demonstrate that both the fungal and the bacterial -glucans are ligands of -glucan-binding sites which are putative receptors for the elicitor signal compounds in soybean roots. Whereas the fungal -glucans stimulate phytoalexin synthesis at low concentrations, the bacterial cyclic 1,3-1,6--glucans appear to be inactive even at relatively high concentrations. Competition studies indicate that increasing concentrations of the bacterial 1,3-1,6--glucans progressively inhibit stimulation of phytoalexin synthesis in a bioassay induced by the fungal 1,3-1,6--glucans. Another type of cyclic -glucan, a 1,2--glucan from Rhizobium meliloti, that does not nodulate on soybean, seems to be inactive as elicitor and as ligand of the -glucan-binding sites. These results may indicate a novel mechanism for a successful plant-symbiont interaction by suppressing the plant's defence response.Abbreviations HG-APEA
1-2-(4-aminophenyl)ethyl]amino-l-hexaglucosyl]deoxyglucitol
- HG-AzPEA
l-2-(4-azidophenyl)-ethyl]amino-l-hexaglucosyl]deoxyglucitol
- IC50
concentration for half-maximal displacement
We thank Ines Arlt for excellent technical assistance. This work was supported by the Deutsche Forschungsgemeinschaft (SFB 369), the Bundesministerium für Bildung, Wissenschaft, Forschung und Technologie, Fonds der Chemischen Industrie (J.E.), and USDA CSRS NRI Competitive Research grant 93373059233 (A.A.B.). |
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Keywords: | Bradyrhizobium Bacterial/fungal 1 3-1 6--glucans" target="_blank">gif" alt="beta" align="MIDDLE" BORDER="0">-glucans Elicitor Glycine Phytoalexins -Glucanbinding sites" target="_blank">gif" alt="beta" align="MIDDLE" BORDER="0">-Glucanbinding sites |
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