十字花科黑腐病菌hrp基因致病功能分析

Pathogenesis analysis of hrp genes in Xanthomonas campestris pv.campestris

通过对Xcc 8004菌株的hrp基因进行逐一敲除,系统研究单个hrp基因对Xcc致病性的贡献。结果表明,9个hrc(hypersensitive response and conserved)基因单独突变后在满身红萝卜上的致病性和在辣椒ECW-10R上激发HR的能力完全丧失;9个hrp基因中,hrpW突变后在辣椒ECW-10R上仍能产生HR,满身红萝卜上致病性减弱,其余hrp基因突变后致病性和过敏反应均丧失;4个hpa(hrp associated protein)基因突变后,hpaA和hpaB突变体完全丧失在满身红萝卜上的毒性也不能在辣椒ECW-10R上引起HR,hpa1和hpaP突变后致病性和HR显著减弱。另外,通过RT-PCR对Xcc 8004 hrp基因簇的每个基因受hrpX和hrpG的调控情况进行分析,结果表明所有hrp基因在不同程度上都受到hrpG、hrpX的正向调控。

Xanthomonas campestris pathovar campestris （Xcc） causes serious black rot in all cruciferous plants worldwide. Gram-negative phytopathogenic bacteria including Xcc cause disease in host plants and trigger a HR （hypersensitive response） in non-hosts or resistant host plant through injecting type III secreted effectors （T3SEs） into host cells. T3SEs are a class of proteins secreted by the conserved type III secretion system （T3SS） which is encoded by hrp cluster. To investigate the functionality of hrp genes per se in hrp cluster, the deletion mutants for each hrp gene were constructed. The results showed that each mutation of the nine hrc genes abolished virulence in Chinese radish and lost HR induction in pepper ECW-10R. As for the nine hrp genes, only the knockout of hrpW triggered a tardy HR and decreased virulence, others lost virulence and HR induction completely. The virulence and the ability to trigger HR abolished in hpaA and hpaB mutants, while the deletion of hpa1 and hpaP reduced virulence and HR significantly. Furthermore, transcription analysis through RT-PCR demonstrated that all members of hrp cluster in Xcc 8004 were activated by hrpG and hrpX at different levels.