An interpromoter region enhances transcription of argk gene, encoding the phaseolotoxin-resistant ornithine carbamoyltransferase in Pseudomonas syringae pv. phaseolicola

Pseudomonas syringae pv. phaseolicola, is the causal agent of halo blight on bean, a disease characterized by water soaked lesions surrounded by a chlorotic halo, which is produced by the action of phaseolotoxin, a nonhost-specific toxin optimally produced between 18°C to 20°C. To protect itself against phaseolotoxin, P. syringae pv. phaseolicola possesses a phaseolotoxin-resistant OCTase (ROCT) encoded by argK, which is expressed under conditions leading to the synthesis of phaseolotoxin. The promoter of argK is divergent to that of phtABC genes and both share an interpromoter region. The objective of the present study was to evaluate the role of the interpromoter region on argK transcription in P. syringae pv. phaseolicola. To this, deletions of the interpromoter region were made and argK expression was evaluated in an heterologous system. Also, the effect of multiple copies of the interpromoter region on phaseolotoxin production was determined. The obtained results showed that this region is necessary to enhance the transcription of argK. Additionally, this region in a multiple copies, interfered with the thermoregulation of phaseolotoxin at 28°C in strain P. syringae pv. phaseolicola NPS3121.