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Title:   Author  item
                                            BHAGWAT, ARVIND - UNIVERSITY OF MARYLANDitem
                                            Pfeffer, Philipitem
                                            Yaklich, Robertitem
                                            Hotchkiss, Arlanditem
                                            CHEN, RONGJI - GUANGXI UNIVERSITY., PRCitem
                                            Keister, Donald
  Submitted to: International Congress on Molecular Plant-Microbe Interactions
                                    Publication Type: Abstract Only
                                    Publication Acceptance Date: 8/26/1999
                                    Publication  Date: N/A
                                    Citation: N/AInterpretive Summary:
                                Technical Abstract: We have isolated and characterized the cyclic beta-(1,3)(1,6)-glucan synthesis locus from Bradyrhizobium japonicum and identified two genes (ndvB,C) which are required for their synthesis and for symbiotic N-fixation. NdvC, supposedly a beta-(1,6)-glucosyl transferase, is a 556 aa polypeptide with several membrane spanning regions.   A single amino  acid alteration  (115 lysine to 115alanine, K115A) was introduced at the putative UDP-glucose binding site and (248 glutamate to 248glutamine, E248Q) at the glucan-binding site.  The expression of mutated NdvC (K115A or E248Q) in a ndvC::Tn5 chromosomal background resulted in cyclic beta-glucans with altered ratios of (1,3)- and (1,6)-linkages. The synthesis of glucans with modified glycosyl linkage patterns allowed B. japonicum strains to infect and nodulate soybean roots, but the symbiosis was ineffective (fix -).  This is contrasted with B. japonicum  strain AB-1 (ndvC::Tn5) which synthesized glucans lacking beta -(1,6)-linkages, (cyclodecakis-(1,3)-beta-D-glucosyl), and formed only pseudonodules devoid of bacteroids.  At 28 days after inoculation, more than 96% of the bacteroids from strain AB-1 carrying the altered ndvC plasmid (pK115A or pE248Q) had lost the plasmid.  More than 85% of the bacteroids with a similar chromosomal background (i.e., ndvC::Tn5), carrying a wild-type beta-(1,6)-glucosyl transferase on plasmid, retained it.  These results indicate that the nodule environment during infection and nodule development selects strains synthesizing wild-type beta-glucan.


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