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Title: BRADYRHIZOBIUM JAPONICUM MUTANTS DEFECTIVE IN CYCLIC BETA-GLUCAN SYNTHESIS SHOW ENHANCED SENSITIVITY TO PLANT DEFENSE REPONSES

Author
item MITHOFER, AXEL - UNIV. OF MUNICH, GERMANY
item Bhagwat, Arvind
item Keister, Donald
item EBEL, JURGEN - UNIV. OF MUNICH, GERMANY

Submitted to: Zeitschrift Fur Naturforschung
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/5/2001
Publication Date: N/A
Citation: N/A

Interpretive Summary: Bradyrhizobium joponicum are beneficial bacterial which form symbiotic associations with soybeans. This symbiosis supplies the plant with a source of nitrogen which can be used for protein synthesis. Improvement of the symbiotic association is important for decreasing the fertilizer nitrogen requirement of soybeans and for sustainable agriculture. Cyclic beta-glucans are small molecules composed solely of glucose, produced by the bacteria and are important in plant-microbe interactions especially in suppressing the plant's defense response, thereby allowing the development of an effective symbiosis. In this manuscript we demonstrated that Bradyrhizobium japonicum mutants, defective in the production of cyclic beta-glucans were more sensitive to phytoalexins (plant defense compounds) than were wild-type bacterial strains. These results support the hypothesis that the cyclic glucans are important in protecting the microbial symbiont during nodule development. These results will be useful for scientists working to understand symbiotic plant-microbe interactions.

Technical Abstract: Susceptibility of the nitrogen-fixing soybean symbiont Bradyrhizobium japonicum to inducible plant defense metabolites such as phytoalexin and H2O2, was investigated. On the wild-type strain USDA 110 the soybean phytoalexin, glyceollin, showed bacteriostatic activity. Viable bacteria isolated from intact nodules were adapted to glyceollin. H2O2 in physiological concentrations did not affect wild-type bacteria. B. japonicum mutants defective in the biosynthesis of cyclic beta-(1-3) -(1-6)-glucans showed higher susceptibility to both phytoalexin and H2O2.