OxyR Positively Influences Phaseolotoxin Synthesis and Pyoverdin Production in Pseudomonas savastanoi pv....

Phaseolotoxin is a major virulence factor of the bean pathogen bacterium P. savastanoi pv. phaseolicola. This toxin plays a key role in the development of the halo blight disease in bean plants. So far, the signal transduction pathways involved in the synthesis of phaseolotoxin have not been elucidated. The influence of regulation mechanisms related to the oxidative stress response, in particular the OxyR protein, it has been suggested to be involved in this process.. In this study we evaluated the role of OxyR in P. savastanoi pv. phaseolicola, mainly compared to the synthesis of phaseolotoxin and the virulence of this phytopathogen. Generation of the oxyR-mutant, pathogenicity and virulence tests, and analyses of gene expression by RT-PCR assays were performed. The results showed that OxyR exerts an effect on the synthesis of phaseolotoxin and positively influences the expression of the Pht and Pbo cluster genes. Likewise, OxyR influences the production of pyoverdine by the control of the expression of the genes encoding the PvdS sigma factor, involved in the synthesis of this pigment. This study is the first report on members of the OxyR regulon of P. savastanoi pv. phaseolicola NPS3121.