Functional Analysis Of KatExoo And CatBxoo Genes Putatively-Encoding Catalases In Hydrogen Peroxide （H₂O₂）Resistence And Virulence Of Xanthomonas Oryzae Pv. Oryzae

Hydrogen peroxide （H₂O₂） is one of critical signal factors, which involved into disease resistanceduring the host and pathogen interactions. In the long-term rice－Xanthomonas oryzae pv. oryzae （Xoo）interaction, ROS is extremely important for rice to prevent from Xoo invasion, while Xoo evolutes toform a set of anti-oxidation system to survive in exposure to high level of ROS （H₂O₂）. Provious studyshowed that the anti-oxidant system is regulated in Xoo by some proteins and OxyRxoo which plays animportant role in exogenous H₂O₂detoxification and is the most important regulatory proteins. It hasbeen shown that some of H₂O₂detoxification genes, such as ahpC/Fxoo、katExoo and catBxoo areup-regulated by OxyRxoo and ahpC/Fxoo plays an important role of endogenous H₂O₂detoxification.However, the specific roles of katExoo and catBxoo of Xoo in exogenous H₂O₂detoxification andbacterial virulence still not clear. The gene cloning, deletion mutagenisis and phynotypic analysis wereperforem in this study by using molecular genetic and plant pathology approaches.1. To reveal the role of katExoo encoding putatively catalase （CAT） in H₂O₂resistance andpathogenicity of Xanthomonas oryzae pv. oryzae, the gene deletion and assays for H₂O₂resistance, CATactivity, in vitro growth, and virulence on rice of the ΔkatExoo mutant were performed in this study.The mutant was generated from Xoo wild-type strain PXO99Athrough marker exchange, in which theconserved domain of CAT （GATase1_catalase and catalase_clade₂） was replaced by GmR. Significantchanges in increased H₂O₂resistance and higher CAT activity were found in the mutant compared toPXO99A. Moreover, remarkable decreases in bacterial growth rate in vitro and in planta of ΔkatExooand diseased leaf lesion of rice were observed. Therefore, katExoo has been shown to play a critical rolein bacterial growth, colonization and pathogenicity on rice.2. To reveal the role of catBxoo encoding putatively catalase （CAT） in H₂O₂resistance andpathogenicity of Xanthomonas oryzae pv. oryzae, the gene deletion and assays for H₂O₂resistance, CATactivity, in vitro growth, and virulence on rice of the ΔcatBxoo mutant were performed in this study.The mutant was generated from Xoo wild-type strain PXO99Athrough marker exchange, in which theconserved domain of CAT （catalase_clade₁） was replaced by GmR. Significant changes in decreasedH₂O₂resistance and lower CAT activity were found in the mutant compared to PXO99A. Moreover,remarkable decreases in bacterial growth rate in vitro and in planta of ΔcatBxoo and diseased leaflesion of rice were observed. Therefore, catBxoo has been shown to play a critical role in bacterialgrowth, colonization and pathogenicity on rice.In conclusion, although katExoo and catBxoo genes play the differential roles in exogenous H₂O₂resistance and CAT activity, both contribute definitely to bacterial full virulence on rice. As a result, thiswork partially provides first genetic evidence to support the hypothesis that KatExoo and CatBxoomight function as the critical regulators of virulence in Xoo.