Microbial Ecology

, Volume 61, Issue 4, pp 723–728

Transcriptome Analysis of the Rhizosphere Bacterium Azospirillum brasilense Reveals an Extensive Auxin Response

  • Sandra Van Puyvelde
  • Lore Cloots
  • Kristof Engelen
  • Frederik Das
  • Kathleen Marchal
  • Jos Vanderleyden
  • Stijn Spaepen
Notes and Short communications

DOI: 10.1007/s00248-011-9819-6

Cite this article as:
Van Puyvelde, S., Cloots, L., Engelen, K. et al. Microb Ecol (2011) 61: 723. doi:10.1007/s00248-011-9819-6

Abstract

The rhizosphere bacterium Azospirillum brasilense produces the auxin indole-3-acetic acid (IAA) through the indole-3-pyruvate pathway. As we previously demonstrated that transcription of the indole-3-pyruvate decarboxylase (ipdC) gene is positively regulated by IAA, produced by A. brasilense itself or added exogenously, we performed a microarray analysis to study the overall effects of IAA on the transcriptome of A. brasilense. The transcriptomes of A. brasilense wild-type and the ipdC knockout mutant, both cultured in the absence and presence of exogenously added IAA, were compared.

Interfering with the IAA biosynthesis/homeostasis in A. brasilense through inactivation of the ipdC gene or IAA addition results in much broader transcriptional changes than anticipated. Based on the multitude of changes observed by comparing the different transcriptomes, we can conclude that IAA is a signaling molecule in A. brasilense. It appears that the bacterium, when exposed to IAA, adapts itself to the plant rhizosphere, by changing its arsenal of transport proteins and cell surface proteins. A striking example of adaptation to IAA exposure, as happens in the rhizosphere, is the upregulation of a type VI secretion system (T6SS) in the presence of IAA. The T6SS is described as specifically involved in bacterium–eukaryotic host interactions. Additionally, many transcription factors show an altered regulation as well, indicating that the regulatory machinery of the bacterium is changing.

Supplementary material

248_2011_9819_MOESM1_ESM.xls (86 kb)
Supplementary Table S1List of differentially expressed genes with a combined response for both exogenous and endogenous IAA. The list is ordered according to ORF number (sheet 1) and cluster number (sheet 2). Sheet 3 contains the RT-qPCR data confirming part of the microarray results (XLS 85 kb).

Copyright information

© Springer Science+Business Media, LLC 2011

Authors and Affiliations

  • Sandra Van Puyvelde
    • 1
  • Lore Cloots
    • 1
  • Kristof Engelen
    • 1
  • Frederik Das
    • 1
  • Kathleen Marchal
    • 1
  • Jos Vanderleyden
    • 1
  • Stijn Spaepen
    • 1
  1. 1.Centre of Microbial and Plant GeneticsK.U.LeuvenHeverleeBelgium

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