The hisC1 gene, encoding aromatic amino acid aminotransferase-1 in Azospirillum brasilense Sp7, expressed in wheat
Background and aims
Production of indole-3-acetic acid (IAA) by Azospirillum brasilense is one of the most important mechanisms underlying the beneficial effects observed in plants after inoculation with this bacterium. This study determined the contribution of the hisC1 gene, which encodes aromatic amino acid aminotransferase-1 (AAT1), to IAA production, and analyzed its expression in the free-living state and in association with the roots of wheat.
We determined production of IAA and AAT activity in the mutant hisC::gusA-sm R . To study the expression of hisC1, a chromosomal gene fusion was analyzed by following β-glucuronidase (GUS) activity in vitro, in the presence of root exudates, and in association with roots.
IAA production in the hisC mutant was not reduced significantly compared to the activity of the wild-type strain. AAT1 activity was reduced by 50% when tyrosine was used as the amino acid donor, whereas there was a 30% reduction when tryptophan was used, compared to the activity of the wild-type strain. Expression of the fusion protein was up-regulated in both logarithmic and stationary phases by several compounds, including IAA, tryptophan, tyrosine, and phenyl acetic acid. We observed the expression of hisC1 in bacteria associated with wheat roots. Root exudates of wheat and maize were able to stimulate hisC1 expression.
The expression data indicate that hisC1 is under a positive feedback control in the presence of root exudates and on plants, suggesting that AAT1 activity plays a role in Azospirillum–plant interactions.
KeywordsAzospirillum brasilense Aromatic amino acid aminotransferase-1 Indole acetic production Radical exudates regulation
Aromatic amino acid aminotransferase-1
Phenyl acetic acid
High-performance liquid chromatography
This work was supported by a Consejo Nacional de Ciencia y Tecnología (CONACyT) Grant 49227-Z, together with Vicerrectoría de investigación y estudios de posgrado-Secretaría de educación pública (VIEP-SEP), Grant NAT-IC-1. J.G.C. was the recipient of a scholarship from CONACyT.
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