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Organization of the ipdC region regulates IAA levels in different Azospirillum brasilense strains: molecular and functional analysis of ipdC in strain SM
Author(s) -
Malhotra Mandira,
Srivastava Sheela
Publication year - 2008
Publication title -
environmental microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.954
H-Index - 188
eISSN - 1462-2920
pISSN - 1462-2912
DOI - 10.1111/j.1462-2920.2007.01529.x
Subject(s) - azospirillum brasilense , strain (injury) , biology , biosynthesis , biochemistry , indole 3 acetic acid , auxin , microbiology and biotechnology , gene , nitrogen fixation , bacteria , genetics , anatomy
Summary Presence of the indole‐3‐pyruvic acid pathway (IPyA) of indole‐3‐acetic acid (IAA) biosynthesis was demonstrated by identifying the ipdC gene encoding indole‐3‐pyruvate decarboxylase (IPDC) in Azospirillum brasilense strain SM. Comparison with other A. brasilense strains, Sp7 and Sp245, revealed homology in the gene and its 5′ regulatory region. The 3′ region of strain SM carries a truncated iaaC gene implicated in controlling IAA biosynthesis in strain Sp245. While the ipdC transcript could be visualized by reverse transcription polymerase chain reaction (RT‐PCR), truncated iaaC was non‐functional. Strain SM derivatives carrying higher copy number of ipdC and P ipdC showed improved IAA biosynthesis. P ipdC showed sequence elements that are part of composite auxin‐responsive promoters. Expression of ipdC was upregulated by IAA, other auxins, temperature and nutrient stress, and an increase in pH. Heterologous overexpression of a functional iaaC gene from strain Sp245 in strain SM confirmed its role in controlling IAA biosynthesis and lowering ipdC expression which may be effected by dissociating IAA–transcriptional regulator interactions in the 5′ region. However, the effect of the introduced iaaC was overcome when both ipdC and iaaC were expressed from similar plasmid background. This analysis confirmed that strain‐based differences in IAA biosynthesis could be explained by differential regulation of ipdC expression.