The Stealth Episome: Suppression of Gene Expression on the Excised Genomic Island PPHGI-1 from Pseudomonas syringae pv. phaseolicola
The Stealth Episome: Suppression of Gene Expression on the Excised Genomic Island PPHGI-1 from Pseudomonas syringae pv. phaseolicola
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DOI：
10.1371/journal.ppat.1002010
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发表时间：
2011-03-01
期刊：
影响因子：
6.7
通讯作者：
Arnold, Dawn L.
中科院分区：
文献类型：
--
作者：
Godfrey, Scott A. C.;Lovell, Helen C.;Arnold, Dawn L.
丁香假单胞菌菜豆（Phaseolicola）是普通菜豆（Phaseolusvulgaris）中的晕斑病的病原体。黑腐病菌菜豆病菌小种4菌株1302 A含有无毒基因avrPphB（syn. hopAR 1），其位于PPHGI-1（一个106 kb的基因组岛）上。PPHGI-1从P.暴露于过敏性抗性反应（HR）后，菜豆株1302 A导致毒力改变的菌株进化。在这里，我们已经使用荧光蛋白报告系统，以获得洞察PPHGI-1的流动性。双标记的P. phaseolicola 1302 A菌株F532（染色体中的dsRFP和PPHGI-1中的eGFP）揭示了在植物感染期间和当在提取的叶质外体流体上体外生长时PPHGI-1：：eGFP编码的荧光的损失。荧光和非荧光PPHGI-1：：eGFP F532群体的荧光激活细胞分选（FACS）显示，细胞不仅在GI缺失时失去荧光，而且在其被切除并作为环状附加体存在时也失去荧光。除了eGFP的表达减少之外，对通过FACS分离的亚群的定量PCR显示，在携带切除的PPHGI-1：：eGFP附加体的F532细胞中，PPHGI-1上的其他基因（avrPphB和xerC）的转录也大大减少。我们的研究结果表明，如何位于移动的致病岛的毒力决定因素可能是隐藏的检测宿主监测系统通过抑制基因表达的附加状态。
Pseudomonas syringae pv. phaseolicola is the causative agent of halo blight in the common bean, Phaseolus vulgaris. P. syringae pv. phaseolicola race 4 strain 1302A contains the avirulence gene avrPphB (syn. hopAR1), which resides on PPHGI-1, a 106 kb genomic island. Loss of PPHGI-1 from P. syringae pv. phaseolicola 1302A following exposure to the hypersensitive resistance response (HR) leads to the evolution of strains with altered virulence. Here we have used fluorescent protein reporter systems to gain insight into the mobility of PPHGI-1. Confocal imaging of dual-labelled P. syringae pv. phaseolicola 1302A strain, F532 (dsRFP in chromosome and eGFP in PPHGI-1), revealed loss of PPHGI-1:: eGFP encoded fluorescence during plant infection and when grown in vitro on extracted leaf apoplastic fluids. Fluorescence-activated cell sorting (FACS) of fluorescent and non-fluorescent PPHGI-1:: eGFP F532 populations showed that cells lost fluorescence not only when the GI was deleted, but also when it had excised and was present as a circular episome. In addition to reduced expression of eGFP, quantitative PCR on sub-populations separated by FACS showed that transcription of other genes on PPHGI-1 (avrPphB and xerC) was also greatly reduced in F532 cells harbouring the excised PPHGI-1:: eGFP episome. Our results show how virulence determinants located on mobile pathogenicity islands may be hidden from detection by host surveillance systems through the suppression of gene expression in the episomal state.