@article{fdi:010073666,
  title = {{R}egulation of nitrogen fixation in {B}radyrhizobium sp. strain {DOA}9 involves two distinct {N}if{A} regulatory proteins that are functionally redundant during symbiosis but not during free-living growth},
  author = {{W}ongdee, {J}. and {B}oonkerd, {N}. and {T}eaumroong, {N}. and {T}ittabutr, {P}. and {G}iraud, {E}ric},
  editor = {},
  language = {{ENG}},
  abstract = {{T}he {B}radyrhizobium sp. {DOA}9 strain displays the unusual properties to have a symbiotic plasmid and to fix nitrogen during both free-living and symbiotic growth. {S}equence genome analysis shows that this strain contains the structural genes of dinitrogenase (nif{DK}) and the nif{A} regulatory gene on both the plasmid and chromosome. {I}t was previously shown that both nif{DK} clusters are differentially expressed depending on growth conditions, suggesting different mechanisms of regulation. {I}n this study, we examined the functional regulatory role of the two nif{A} genes found on the plasmid (nif{A}p) and chromosome (nif{A}c) that encode proteins with a moderate level of identity (55%) and different structural architectures. {U}sing gus{A} (beta-glucuronidase) reporter strains, we showed that both nif{A} genes were expressed during both the free-living and symbiotic growth stages. {D}uring symbiosis with {A}eschynomene americana, mutants in only one nif{A} gene were not altered in their symbiotic properties, while a double nif{A} mutant was drastically impaired in nitrogen fixation, indicating that the two {N}if{A} proteins are functionally redundant during this culture condition. {I}n contrast, under in vitro conditions, the nif{A}c mutant was unable to fix nitrogen, and no effect of the nif{A}p mutation was detected, indicating that {N}if{A}c is essential to activate nif genes during free-living growth. {I}n accordance, the nitrogenase fixation deficiency of this mutant could be restored by the introduction of nif{A}c but not by nif{A}p or by two chimeric nif{A} genes encoding hybrid proteins with the {N}-terminus part of {N}if{A}c and the {C}-terminus of {N}if{A}p. {F}urthermore, transcriptional analysis by {RT}-q{PCR} of the {WT} and two nif{A} mutant backgrounds showed that {N}if{A}c and {N}if{A}p activated the expression of both chromosome and plasmid structural nif{DK} genes during symbiosis, while only {N}if{A}c activated the expression of nif{DK}c during free-living conditions. {I}n summary, this study provides a better overview of the complex mechanisms of regulation of the nitrogenase genes in the {DOA}9 strain that involve two distinct {N}if{A} proteins, which are exchangeable during symbiosis for the activation of nif genes but not during free-living growth where {N}if{A}c is essential for the activation of nif{DK}c.},
  keywords = {{N}if{A} ; {B}radyrhizobium ; symbiosis ; legume ; nitrogen ; nitrogenase ; {R}hizobium},
  booktitle = {},
  journal = {{F}rontiers in {M}icrobiology},
  volume = {9},
  numero = {},
  pages = {art. 1644 [11 p.]},
  ISSN = {1664-302{X}},
  year = {2018},
  DOI = {10.3389/fmicb.2018.01644},
  URL = {https://www.documentation.ird.fr/hor/fdi:010073666},
}