Open AccessTranscriptional Analysis of the Azospirillum brasilense Indole-3-Pyruvate Decarboxylase Gene and Identification of a cis-Acting Sequence Involved in Auxin Responsive Expression
Author(s) -
Ann Vande Broek,
Peter Gysegom,
Ositadinma Ona,
Nico Hendrickx,
Els Prinsen,
Jan Van Impe,
Jos Vanderleyden
Publication year - 2005
Publication title -
molecular plant-microbe interactions
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.565
H-Index - 153
eISSN - 1943-7706
pISSN - 0894-0282
DOI - 10.1094/mpmi-18-0311
Subject(s) - operon , azospirillum brasilense , biology , gene , pyruvate decarboxylase , gal operon , biochemistry , escherichia coli , microbiology and biotechnology , genetics , enzyme , bacteria , nitrogen fixation , alcohol dehydrogenase
of the Azospirillum brasilense ipdC gene, encoding an indole-3-pyruvate decarboxylase, a key enzyme in the production of indole-3-acetic acid (IAA) in this bacterium, is upregulated by IAA. Here, we demonstrate that the ipdC gene is the promoter proximal gene in a bicistronic operon. Database searches revealed that the second gene of this operon, named iaaC, is well conserved evolutionarily and that the encoded protein is homologous to the Escherichia coli protein SCRP-27A, the zebrafish protein ES1, and the human protein KNP-I/GT335 (HES1), all of unknown function and belonging to the DJ-1/PfpI superfamily. In addition to this operon structure, iaaC is also transcribed monocistronically. Mutation analysis of the latter gene indicated that the encoded protein is involved in controlling IAA biosynthesis but not ipdC expression. Besides being upregulated by IAA, expression of the ipdC-iaaC operon is pH dependent and maximal at acidic pH. The ipdC promoter was studied using a combination of deletion analyses and site-directed mutagenesis. A dyadic sequence (ATTGTTTC(GAAT)GAAACAAT), centered at -48 was demonstrated to be responsible for the IAA inducibility. This bacterial auxin-responsive element does not control the pH-dependent expression of ipdC-iaaC.