Suppression of fungal β-glucan-induced plant defence in soybean (Glycine maxL.) by cyclic 1,3-1,6-β-glucans from the symbiontBradyrhizobium japonicum
✍ Scribed by Axel Mithöfer; Arvind A. Bhagwat; Markus Feger; Jürgen Ebel
- Publisher
- Springer-Verlag
- Year
- 1996
- Tongue
- English
- Weight
- 718 KB
- Volume
- 199
- Category
- Article
- ISSN
- 0032-0935
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✦ Synopsis
The production ofantimicrobial 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 1,6-13glucans 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 1,3-1,6-13-glucans. Here we demonstrate that both the fungal and the bacterial 13-glucans are ligands of [3glucan-binding sites which are putative receptors for the elicitor signal compounds in soybean roots. Whereas the fungal 13-glucans stimulate phytoalexin synthesis at low concentrations, the bacterial cyclic 1,3-1,6-13-glucans appear to be inactive even at relatively high concentrations.
Competition studies indicate that increasing concentrations of the bacterial 1,3 1,6-[3-glucans progressively inhibit stimulation of phytoalexin synthesis in a bioassay induced by the fungal 1,3-1,6-[3-glucans. Another type of cyclic 13-glucan, a 1,2-[3-glucan from Rhizobium meliloti, that does not nodulate on soybean, seems to be inactive as elicitor and as ligand of the 13-glucan-binding sites. These results may indicate a novel mechanism for a successful plant-symbiont interaction by suppressing the plant's defence response.