نبذة مختصرة : Background To facilitate infection, Xanthomonas oryzae pv. oryzae ( Xoo ), the bacterial blight pathogen of rice, needs to degrade hydrogen peroxide (H 2 O 2 ) generated by the host defense response via a mechanism that is mediated by the transcriptional regulator OxyR. The catalase (CAT) gene catB has previously been shown to belong to the OxyR regulon in Xoo . However, its expression patterns and function in H 2 O 2 detoxification and bacterial pathogenicity on rice remain to be elucidated. Results The catB gene encodes a putative catalase and is highly conserved in the sequenced strains of Xanthomonas spp. β-galactosidase analysis and electrophoretic mobility shift assays (EMSA) showed that OxyR positively regulated the transcription of catB by directly binding to its promoter region. The quantitative real-time PCR (qRT-PCR) assays revealed that the expression levels of catB and oxyR were significantly induced by H 2 O 2 . Deletion of catB or oxyR drastically impaired bacterial viability in the presence of extracellular H 2 O 2 and reduced CAT activity, demonstrating that CatB and OxyR contribute to H 2 O 2 detoxification in Xoo . In addition, Δ catB and Δ oxyR displayed shorter bacterial blight lesions and reduced bacterial growth in rice compared to the wild-type stain, indicating that CatB and OxyR play essential roles in the virulence of Xoo . Conclusions Transcription of catB is enhanced by OxyR in response to exogenous H 2 O 2 . CatB functions as an active catalase that is required for the full virulence of Xoo in rice.
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