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  • Title: Molecular cloning and sequence analysis of an Azospirillum brasilense indole-3-pyruvate decarboxylase gene.
    Author: Costacurta A, Keijers V, Vanderleyden J.
    Journal: Mol Gen Genet; 1994 May 25; 243(4):463-72. PubMed ID: 8202090.
    Abstract:
    Azospirillum brasilense isolated from the rhizosphere of different plants has the ability to excrete indole-3-acetic acid (IAA) into the culture media. Cosmid p0.2, isolated from an A. brasilense Sp245 genome library in pLAFR1, complements the Tn5-induced mutant SpM7918 of A. brasilense Sp6 which excretes reduced amounts of IAA. Restriction mapping and gene expression studies identified a BglII-EcoRI 4.3 kb fragment of p0.2 sufficient for the restoration of high levels of IAA production in mutant SpM7918. Tn5 mutagenesis localized the gene responsible on a 1.8 kb SmaI fragment. Nucleotide sequence analysis revealed that this fragment contains one complete open reading frame. The predicted protein sequence shows extensive homology with the indole-3-pyruvate decarboxylase of Enterobacter cloacae and the pyruvate decarboxylases of Saccharomyces cerevisiae and Zymomonas mobilis. The A. brasilense mutant Sp245a, constructed by homogenotization of a Tn5 insertion derivative of the 1.8 kb SmaI fragment, also displayed reduced IAA production. Introduction of the cloned wild-type gene into Rhizobium meliloti 1021 resulted in increased IAA production. Cell-free extracts prepared from R. meliloti and A. brasilense transconjugants harboring this gene could convert indole-3-pyruvic acid to indole-3-acetaldehyde and tryptophol. These results clearly demonstrate that IAA production in A. brasilense is mediated by indole-3-pyruvate decarboxylase.
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