Identification and characterization of the two-component NtrY/NtrX regulatory system in Azospirillum brasilense

• Published in: Brazilian journal of medical and biological research Vol. 35; no. 6; pp. 651 - 661
• Main Authors: Ishida, M L, Assumpção, M C, Machado, H B, Benelli, E M, Souza, E M, Pedrosa, F O
• Format: Journal Article
• Language: English
• Published: Brazil Associação Brasileira de Divulgação Científica 01-06-2002
• Subjects: Amino Acid Sequence; Azospirillum brasilense; Azospirillum brasilense - genetics; Azospirillum brasilense - growth & development; Azospirillum brasilense - isolation & purification; Bacterial Proteins - isolation & purification; Base Sequence; BIOLOGY; DNA, Bacterial - genetics; Escherichia coli - chemistry; Gene Expression Regulation, Bacterial - genetics; Genes, Bacterial; Genetic Complementation Test; MEDICINE, RESEARCH & EXPERIMENTAL; Molecular Sequence Data; Mutation; Nitrogen Fixation - genetics; Nitrogen regulation; ntrBC genes; ntrYX genes; Two-component regulatory system; Azospirillum brasilense; Nitrogen regulation; ntrYX genes; ntrBC genes; Two-component regulatory system
• ISSN: 0100-879X; 1414-431X; 0100-879X; 1414-431X
• DOI: 10.1590/s0100-879x2002000600004

Two Azospirillum brasilense open reading frames (ORFs) exhibited homology with the two-component NtrY/NtrX regulatory system from Azorhizobium caulinodans. These A. brasilense ORFs, located downstream to the nifR3ntrBC operon, were isolated, sequenced and characterized. The present study suggests that ORF1 and ORF2 correspond to the A. brasilense ntrY and ntrX genes, respectively. The amino acid sequences of A. brasilense NtrY and NtrX proteins showed high similarity to sensor/kinase and regulatory proteins, respectively. Analysis of lacZ transcriptional fusions by the beta-galactosidase assay in Escherichia coli ntrC mutants showed that the NtrY/NtrX proteins failed to activate transcription of the nifA promoter of A. brasilense. The ntrYX operon complemented a nifR3ntrBC deletion mutant of A. brasilense for nitrate-dependent growth, suggesting a possible cross-talk between the NtrY/X and NtrB/C sensor/regulator pairs. Our data support the existence of another two-component regulatory system in A. brasilense, the NtrY/NtrX system, probably involved in the regulation of nitrate assimilation.