Regulatory role of Rhizobium etli CNPAF512 fnrN during symbiosis.
The Rhizobium etli CNPAF512 fnrN gene was identified in the fixABCX rpoN(2) region. The corresponding protein contains the hallmark residues characteristic of proteins belonging to the class IB group of Fnr-related proteins. The expression of R. etli fnrN is highly induced under free-living microaerobic conditions and during symbiosis. This microaerobic and symbiotic induction of fnrN is not controlled by the sigma factor RpoN and the symbiotic regulator nifA or fixLJ, but it is due to positive autoregulation. Inoculation of Phaseolus vulgaris with an R. etli fnrN mutant strain resulted in a severe reduction in the bacteroid nitrogen fixation capacity compared to the wild-type capacity, confirming the importance of FnrN during symbiosis. The expression of the R. etli fixN, fixG, and arcA genes is strictly controlled by fnrN under free-living microaerobic conditions and in bacteroids during symbiosis with the host. However, there is an additional level of regulation of fixN and fixG under symbiotic conditions. A phylogenetic analysis of the available rhizobial FnrN and FixK proteins grouped the proteins in three different clusters.
Centre of Microbial and Plant Genetics, Katholieke Universiteit Leuven, B-3001 Heverlee, Belgium.
Martine
M
Moris
Bruno
B
Dombrecht
Chuanwu
C
Xi
Jos
J
Vanderleyden
Jan
J
Michiels
D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics / Q000502:physiology; D001483:Base Sequence; D002874:Chromosome Mapping; D003001:Cloning, Molecular; D004269:DNA, Bacterial / Q000235:genetics; D007887:Fabaceae / Q000382:microbiology; D015964:Gene Expression Regulation, Bacterial; D005798:Genes, Bacterial; D008954:Models, Biological; D008969:Molecular Sequence Data; D009154:Mutation; D009586:Nitrogen Fixation / Q000235:genetics; D010641:Phenotype; D010802:Phylogeny; D042163:Rhizobium etli / Q000235:genetics* / Q000502:physiology*; D016962:Sinorhizobium meliloti / Q000235:genetics; D013559:Symbiosis / Q000235:genetics*
D001426:Bacterial Proteins; D004269:DNA, Bacterial