Auxins upregulate expression of the indole-3-pyruvate decarboxylase gene in Azospirillum brasilense

Transcription of the Azospirillum brasilense ipdC gene, encoding an indole- 3-pyruvate decarboxylase involved in the biosynthesis of indole-3-acetic ac id (IAA), is induced by IAA as determined by ipdC-gusA expression studies a nd Northern analysis. Besides IAA, exogenously added synthetic auxins such as 1-naphthaleneacetic acid, 2,4-dichlorophenoxypropionic acid, and p-chlor ophenoxyacetic acid were also found to upregulate ipdC expression, No upreg ulation was observed with tryptophan, acetic acid, or propionic acid or wit h the IAA conjugates IAA ethyl ester and IAA-L-phenylalanine, indicating st ructural specificity is required for ipdC induction. This is the first repo rt describing the induction of a bacterial gene by auxin.