Submitted to: American Society for Microbiology
Publication Type: Abstract Only
Publication Acceptance Date: 5/21/2000
Publication Date: N/A
Citation: Interpretive Summary:
Technical Abstract: The soybean microsymbiont, Bradyrhizobium japonicum synthesizes cyclic B-(1,3), (1,6)-glucans during nodule development. The function of cyclic glucans in free-living bacteria is periplasmic osmoprotection. The role in symbiotic interactions is not yet clear but we have postulated a role in the suppression of host-defense responses. Previously, we identified two genes (ndvB, ndvC) that are required for cyclic B-(1,3),(1,6)-glucan synthesis and successful symbiotic interactions with host soybean. Mutation of ndvB completely abolished glucan synthesis, while mutation of ndvC resulted in synthesis of glucans with only B-(1,3)-linkages. In addition to the symbiotic defect, the ndvB mutant is non-motile and hypoosmotically sensitive, whereas the ndvC mutant is motile and osmotically competent. Recently, a new open reading frame (ORF1) was located between ndvB and ndvC by complete sequencing of the ndvB, C region. It was identified as a third gene (ndvD) involved in cyclic B-glucan synthesis by creating the ORF1-ndvB deletion mutant RC-1 and then complementing RC-1 with plasmids carrying various combinations of ndvB, ORF1 and ndvC. An ndvD mutant was created using site-directed Tn5 insertion mutagenesis followed by homogenotization. The ndvD mutant is non-motile and symbiotically defective. Symbiotic function was restored by complementing with plasmids carrying a functional ndvD. Thus the ndvD gene is required for significant levels of glucan synthesis and successful symbiotic interactions with host soybean. This work was supported in part by award USDA NRI CRGP 9803542 to A.A.B. and D.L. K..