A role for Bradyrhizobium japonicum ECF16 sigma factor EcfS in the formation of a functional symbiosis with soybean

Mol Plant Microbe Interact. 2012 Jan;25(1):119-28. doi: 10.1094/MPMI-07-11-0188.


Alternative sigma (σ) factors, proteins that recruit RNA polymerase core enzyme to target promoters, are one mechanism by which bacteria transcriptionally regulate groups of genes in response to environmental stimuli. A class of σ(70) proteins, termed extracytoplasmic function (ECF) σ factors, are involved in cellular processes such as bacterial stress responses and virulence. Here, we describe an ECF16 σ factor, EcfS (Blr4928) from the gram-negative soil bacterium Bradyrhizobium japonicum USDA110, that plays a critical role in the establishment of a functional symbiosis with soybean. Nonpolar insertional mutants of ecfS form immature nodules that do not fix nitrogen, a defect that can be successfully complemented by expression of ecfS. Overexpression of the cocistronic gene, tmrS (blr4929), phenocopies the ecfS mutant in planta and, therefore, we propose that TmrS is a negative regulator of EcfS, a determination consistent with the prediction that it encodes an anti-σ factor. Microarray analysis of the ecfS mutant and tmrS overexpressor was used to identify 40 transcripts misregulated in both strains. These transcripts primarily encode proteins of unknown and transport-related functions and may provide insights into the symbiotic defect in these strains.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Bacterial Proteins / genetics
  • Bacterial Proteins / metabolism
  • Bradyrhizobium / genetics
  • Bradyrhizobium / metabolism*
  • Bradyrhizobium / physiology
  • DNA, Complementary / genetics
  • Gene Expression / genetics
  • Gene Expression Profiling
  • Gene Expression Regulation, Bacterial / genetics*
  • Genes, Bacterial / genetics
  • Genetic Complementation Test
  • Mutagenesis, Insertional
  • Nitrogen Fixation
  • Oligonucleotide Array Sequence Analysis
  • Phenotype
  • Plant Leaves / microbiology
  • RNA, Bacterial / genetics
  • RNA, Messenger / genetics
  • Root Nodules, Plant / microbiology
  • Root Nodules, Plant / ultrastructure
  • Sigma Factor / genetics
  • Sigma Factor / metabolism*
  • Soybeans / microbiology*
  • Soybeans / ultrastructure
  • Stress, Physiological
  • Symbiosis
  • Transcription, Genetic
  • Transcriptome


  • Bacterial Proteins
  • DNA, Complementary
  • RNA, Bacterial
  • RNA, Messenger
  • Sigma Factor