title: phrR-like gene praR of Azorhizobium caulinodans ORS571 is essential for symbiosis with Sesbania rostrata and is involved in expression of reb genes.
abstract: This study focuses on the function of the gene praR that encodes a putative transcription factor in Azorhizobium caulinodans ORS571, a microsymbiont of Sesbania rostrata. The praR gene is a homolog of the phrR gene of Sinorhizobium medicae WSM419, and the praR and phrR homologs are distributed throughout the class Alphaproteobacteria. The growth and nitrogen fixation activity of an A. caulinodans praR deletion mutant in the free-living state were not significantly different from those of the wild-type strain. However, the stem nodules formed by the praR mutant showed lower nitrogen fixation activity than the wild-type stem nodules. Microscopy revealed that infected host cells with an oval or elongated shape were observed at early stages in the nodules formed by the praR mutant, but these infected cells gradually fell into two types. One maintained an oval or elongated shape, but the vacuoles in these cells gradually enlarged and the bacteria gradually disappeared. The other cells were shrunken with bacteria remaining inside. Microarrays revealed that genes homologous to the reb genes of Caedibacter taeniospiralis were highly expressed in the praR mutant. Furthermore, the stem nodules formed by an A. caulinodans mutant with a deletion of praR and reb-homologous genes showed high nitrogen fixation activity, comparable to that of the wild-type stem nodules, and were filled with oval or elongated host cells. These results suggest that PraR controls the expression of the reb-homologous genes and that high expression of reb-homologous genes causes aberrance in A. caulinodans-S. rostrata symbiosis.
authors.affiliation: Biotechnology Research Center, The University of Tokyo, Yayoi 1-1-1, Bunkyo-ku, Tokyo, Japan.
authors.forename: Noriko
authors.initials: N
authors.lastname: Akiba
authors.forename: Toshihiro
authors.initials: T
authors.lastname: Aono
authors.forename: Hiroki
authors.initials: H
authors.lastname: Toyazaki
authors.forename: Satoru
authors.initials: S
authors.lastname: Sato
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Oyaizu
mesh_terms: D020599:Azorhizobium caulinodans / Q000235:genetics / Q000502:physiology*; D001426:Bacterial Proteins / Q000235:genetics / Q000502:physiology*; D017353:Gene Deletion; D020869:Gene Expression Profiling; D015964:Gene Expression Regulation, Bacterial; D008853:Microscopy; D009586:Nitrogen Fixation; D018517:Plant Roots / Q000166:cytology / Q000382:microbiology; D017386:Sequence Homology, Amino Acid; D049931:Sesbania / Q000166:cytology / Q000382:microbiology*; D013559:Symbiosis; D014157:Transcription Factors / Q000235:genetics / Q000502:physiology*
chemical_list: D001426:Bacterial Proteins; D014157:Transcription Factors
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