Effects of indole-3-acetic acid on the transcriptional activities and stress tolerance of Bradyrhizobium japonicum

PLoS One. 2013 Oct 2;8(10):e76559. doi: 10.1371/journal.pone.0076559. eCollection 2013.


A genome-wide transcriptional profile of Bradyrhizobium japonicum, the nitrogen-fixing endosymbiont of the soybean plant, revealed differential expression of approximately 15% of the genome after a 1 mM treatment with the phytohormone indole-3-acetic acid (IAA). A total of 1,323 genes were differentially expressed (619 up-regulated and 704 down-regulated) at a two-fold cut off with q value ≤ 0.05. General stress response genes were induced, such as those involved in response to heat, cold, oxidative, osmotic, and desiccation stresses and in exopolysaccharide (EPS) biosynthesis. This suggests that IAA is effective in activating a generalized stress response in B. japonicum. The transcriptional data were corroborated by the finding that stress tolerance of B. japonicum in cell viability assays was enhanced when pre-treated with 1 mM IAA compared to controls. The IAA treatment also stimulated biofilm formation and EPS production by B. japonicum, especially acidic sugar components in the total EPS. The IAA pre-treatment did not influence the nodulation ability of B. japonicum. The data provide a comprehensive overview of the potential transcriptional responses of the symbiotic bacterium when exposed to the ubiquitous hormone of its plant host.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Bacterial Proteins / genetics*
  • Bacterial Proteins / metabolism
  • Biofilms / drug effects
  • Biofilms / growth & development
  • Bradyrhizobium / drug effects*
  • Bradyrhizobium / genetics
  • Bradyrhizobium / metabolism
  • Gene Expression Profiling
  • Gene Expression Regulation, Bacterial / drug effects*
  • Genome, Bacterial*
  • Indoleacetic Acids / pharmacology*
  • Microbial Viability / drug effects
  • Plant Growth Regulators / pharmacology*
  • Polysaccharides, Bacterial / biosynthesis
  • Polysaccharides, Bacterial / genetics
  • Soybeans / microbiology
  • Stress, Physiological
  • Symbiosis / physiology
  • Transcription, Genetic / drug effects*


  • Bacterial Proteins
  • Indoleacetic Acids
  • Plant Growth Regulators
  • Polysaccharides, Bacterial
  • indoleacetic acid

Grant support

This research was supported in part by a Research Enhancement Program (REP) grant from the University of Texas-Arlington. UTA Grant Number is 14-7488-34. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. No additional external funding received for this study.