title: Transcriptome analysis of the rhizosphere bacterium Azospirillum brasilense reveals an extensive auxin response.
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.
authors.affiliation: Centre of Microbial and Plant Genetics, K.U.Leuven, Kasteelpark Arenberg 20-Bus 2460, 3001 Heverlee, Belgium.
authors.forename: Sandra
authors.initials: S
authors.lastname: Van Puyvelde
authors.forename: Lore
authors.initials: L
authors.lastname: Cloots
authors.forename: Kristof
authors.initials: K
authors.lastname: Engelen
authors.forename: Frederik
authors.initials: F
authors.lastname: Das
authors.forename: Kathleen
authors.initials: K
authors.lastname: Marchal
authors.forename: Jos
authors.initials: J
authors.lastname: Vanderleyden
authors.forename: Stijn
authors.initials: S
authors.lastname: Spaepen
mesh_terms: D015806:Azospirillum brasilense / Q000235:genetics* / Q000378:metabolism*; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D020869:Gene Expression Profiling; D015964:Gene Expression Regulation, Bacterial; D007210:Indoleacetic Acids / Q000378:metabolism*; D008969:Molecular Sequence Data; D058441:Rhizosphere
chemical_list: D001426:Bacterial Proteins; D007210:Indoleacetic Acids