The phytopathogenXanthomonas campestrisutilizes the divergently transcribedpobA/pobRlocus for 4-hydroxybenzoic acid recognition and degradation to promote virulence

文献类型： 外文期刊

第一作者： Chen, Bo

作者： Chen, Bo;Qiu, Jia-Hui;Song, Kai;He, Ya-Wen;Li, Rui-Fang;Zhou, Lian;Tang, Ji-Liang

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关键词： 4-hydroxybenzoic acid; pathogenicity; pobA; pobR; Xanthomonas campestris

期刊名称：MOLECULAR MICROBIOLOGY （ 影响因子：3.501； 五年影响因子：3.996 ）

ISSN： 0950-382X

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收录情况： SCI

摘要： Xanthomonas campestrispv.campestris(Xcc) is the causal agent of black rot in crucifers. Our previous findings revealed thatXcccan degrade 4-hydroxybenzoic acid (4-HBA) via the beta-ketoadipate pathway. This present study expands on this knowledge in several ways. First, we show that infectiveXcccells induce in situ biosynthesis of 4-HBA in host plants, andXcccan efficiently degrade 4-HBA via thepobA/pobRlocus, which encodes a 4-hydroxybenzoate hydroxylase and an AraC-family transcription factor respectively. Next, the transcription ofpobAis specifically induced by 4-HBA and is positively regulated by PobR, which is constitutively expressed inXcc. 4-HBA directly binds to PobR dimers, resulting in activation ofpobAexpression. Point mutation and subsequent isothermal titration calorimetry and size exclusion chromatography analysis identified nine key conserved residues required for 4-HBA binding and/or dimerization of PobR. Furthermore, overlapping promoters harboring fully overlapping -35 elements were identified between the divergently transcribedpobAandpobR. The 4-HBA/PobR dimer complex specifically binds to a 25-bp site, which encompasses the -35 elements shared by the overlapping promoters. Finally, GUS histochemical staining and subsequent quantitative assay showed that bothpobAandpobRgenes are transcribed duringXccinfection of Chinese radish, and the strain Delta pobRexhibited compromised virulence in Chinese radish. These findings suggest that the ability ofXccto survive the 4-HBA stress might be important for its successful colonization of host plants.

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