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United States Department of Agriculture

Agricultural Research Service

Title: DO CYCLIC B-(1-3)(1-6)-GLUCANS OF BRADYRHIZOBIUM JAPONICUM ACT AS SUPPRESSORS OF HOST DEFENSE RESPONSE DURING SOYBEAN ROOT NODULE DEVELOPMENT?)

Author
item Mithofer, Axel
item Bhagwat, Arvind
item Pfeffer, Philip
item Kraus, Christine
item Ebel, Jurgen
item Keister, Donald

Submitted to: International Congress on Molecular Plant-Microbe Interactions
Publication Type: Abstract only
Publication Acceptance Date: 8/30/1996
Publication Date: N/A
Citation:

Interpretive Summary:

Technical Abstract: The soybean microsymbiont Bradyrhizobium japonicum synthesizes cyclic B-(1-3),B-(1-6)-glucans which function as osmoprotectants during hypoosmotic growth conditions. The microsymbiont synthesizes the glucans throughout nodule development. Mutants of B. japonicum defective in the synthesis of cyclic B-(1-3),(1-6)-glucans are unable to establish a successful symbiotic interaction with soybean. Although bradyrhizobial glucans share some structual similarity with one of the best characterized elicitors from Phytophthora sojae [cell-wall B-(1-3),(1-6)-branched glucans], they are weak inducers of phytoalexin synthesis. However when tested in combination, B. japonicum cyclic B-glucans inhibited stimulation of phytoalexin accumulation by fungal glucans in a concentration dependent manner. In assays with a radio-labeled photoaffinity conjugate of the hepta-B-glucoside elicitor and solubilized B-glucan binding protein (Mr=75 kDa) from soybean plasma membranes, the the cyclic B-glucans of B. japonicum competitively inhibited binding of the fungal elicitor. The ndvC mutant of B. japonicum produces glucans predominantly of B-(1-3)-linkages, with a ring containing 6 to 8 glucose residues and DP=12 (cyclolaminarinose). This mutant formed nodule-like structures containing phytoalexin levels four-times higher than wild-type. Binding studies of cyclic B-glucan binding protein will be reported which which suggest a novel role for the microsymbiont's cyclic B-glucans as suppressors of the host defense response.

Last Modified: 8/24/2016
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