title: A novel genetic locus outside the symbiotic island is required for effective symbiosis of Bradyrhizobium japonicum with soybean Glycine max.
abstract: In order to investigate the symbiotic interaction between soybean and Bradyrhizobium japonicum, TnphoA mutagenesis of the microsymbiont was performed. Mutant strain 2-10 was found to induce a strongly reduced number of ineffective nodules. Ultrastructural analysis of the soybean nodule central tissue revealed the presence of numerous starch granules and vacuoles in the infected cells. In addition, the number of symbiosomes was extremely low, indicating an impaired interaction between the plant and invading bacteria. Cloning and sequencing of the mutated DNA region uncovered four open reading frames (ORFs) lacking any data base similarities. ORFs srrA1 and srrA2, the 2-10 TnphoA insertion site, are encoded in the same reading frame. A 35-kDa expression product in Escherichia coli indicated the presence of a common protein, called SrrA (symbiotically relevant region) in B. japonicum 110spc4, encoded by combined srrA1 and srrA2 genes. The analysis of gene disruption mutants revealed that srrB and srrC were also required for effective symbiosis with soybeans. Further downstream the gene for a putative inner membrane protein (pipA) of unknown function was encoded on the opposite strand. Primer extension studies led to the conclusion that the organization of genes differed from the RhizoBase annotation in this particular region of B. japonicum USDA110.
authors.affiliation: Philipps University of Marburg, Faculty of Biology, Cell Biology and Applied Botany, Karl-von-Frisch-Str. 8, 35032 Marburg, Germany.
authors.forename: Bernd Ulrich
authors.initials: BU
authors.lastname: Becker
authors.forename: Nathalie
authors.initials: N
authors.lastname: Bonnard
authors.forename: Vincent
authors.initials: V
authors.lastname: Boiffin
authors.forename: Erhard
authors.initials: E
authors.lastname: Mörschel
authors.forename: Alvaro
authors.initials: A
authors.lastname: Tresierra
authors.forename: Peter
authors.initials: P
authors.lastname: Müller
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism; D001483:Base Sequence; D020369:Bradyrhizobium / Q000235:genetics*; D017353:Gene Deletion; D015964:Gene Expression Regulation, Bacterial; D008969:Molecular Sequence Data; D016254:Mutagenesis, Insertional; D013025:Glycine max / Q000382:microbiology*; D013559:Symbiosis / Q000235:genetics
chemical_list: D001426:Bacterial Proteins