The MexE/MexF/AmeC Efflux Pump of Agrobacterium tumefaciens and Its Role in Ti Plasmid Virulence Gene Expression
The MexE/MexF/AmeC Efflux Pump of Agrobacterium tumefaciens and Its Role in Ti Plasmid Virulence Gene Expression
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DOI：
10.1128/jb.00609-19
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发表时间：
2020-04-01
影响因子：
3.2
通讯作者：
Zhao, Jinlei
中科院分区：
文献类型：
--
作者：
Binns, Andrew N.;Zhao, Jinlei
根癌农杆菌的致瘤(Ti)质粒毒力基因的表达是将DNA从根癌农杆菌转移到植物细胞中所必需的，最终导致植物肿瘤的发生。VIR基因是由于暴露于某些苯酚衍生物、单糖和细胞外环境中的低pH而诱导的。土壤以及植物上的伤口部位-这种细菌毒力活动的通常部位-可以包含这些信号，但在土壤中表达病毒基因将是对能源的浪费。这表明，可能存在机制，以确保VIR基因的表达只发生在较高浓度的诱导剂，通常在植物伤口部位。为了寻找影响3，5-二甲氧基-4-羟基苯乙酮(AS)毒力基因诱导活性敏感性的转座子介导的突变，鉴定出与铜绿假单胞菌Mexe/MexF/OprN泵同源的RND型外排泵。携带泵组分插入或缺失的突变体的表型包括对As诱导病毒的超敏、烟草叶片外植体毒力测定的超敏和对氯霉素的毒性超敏。此外，AS苯酚环上的甲氧基取代基对于识别作为泵浦底物似乎是关键的。这些结果支持这样一种假设，即毒力基因表达的调控与细胞活动相结合，从而提高诱导所需的植物来源诱导物的水平，从而使这一现象优先发生在植物环境中。控制细菌病原菌毒力活动的基因的重要表达预计优先发生在易受该病原体影响的宿主部位。在植物病原体根癌农杆菌中诱导这种活性的宿主衍生分子存在于土壤和植物中。在这里，我们测试了这样的假设，即通过选择对毒力基因诱导分子高度敏感的突变细菌，存在抑制农杆菌物种对毒力基因诱导分子的敏感性的机制。已鉴定的突变基因编码一个外排泵，其拟议的活性增加了病毒基因表达所需的诱导剂的浓度；该泵还参与了抗生素耐药性，证明了细胞防御活性与农杆菌毒力控制之间的关系。
Expression of the tumor-inducing (Ti) plasmid virulence genes of Agrobacterium tumefaciens is required for the transfer of DNA from the bacterium into plant cells, ultimately resulting in the initiation of plant tumors. The vir genes are induced as a result of exposure to certain phenol derivatives, monosaccharides, and low pH in the extracellular milieu. The soil, as well as wound sites on a plant-the usual site of the virulence activity of this bacterium-can contain these signals, but vir gene expression in the soil would be a wasteful utilization of energy. This suggests that mechanisms may exist to ensure that vir gene expression occurs only at the higher concentrations of inducers typically found at a plant wound site. In a search for transposon-mediated mutations that affect sensitivity for the virulence gene-inducing activity of the phenol, 3,5-dimethoxy-4-hydroxyacetophenone (acetosyringone [AS]), an RND-type efflux pump homologous to the MexE/MexF/OprN pump of Pseudomonas aeruginosa was identified. Phenotypes of mutants carrying an insertion or deletion of pump components included hypersensitivity to the virinducing effects of AS, hypervirulence in the tobacco leaf explant virulence assay, and hypersensitivity to the toxic effects of chloramphenicol. Furthermore, the methoxy substituents on the phenol ring of AS appear to be critical for recognition as a pump substrate. These results support the hypothesis that the regulation of virulence gene expression is integrated with cellular activities that elevate the level of plant-derived inducers required for induction so that this occurs preferentially, if not exclusively, in a plant environment.IMPORTANCE Expression of genes controlling the virulence activities of a bacterial pathogen is expected to occur preferentially at host sites vulnerable to that pathogen. Host-derived molecules that induce such activities in the plant pathogen Agrobacterium tumefaciens are found in the soil, as well as in the plant. Here, we tested the hypothesis that mechanisms exist to suppress the sensitivity of Agrobacterium species to a virulence gene-inducing molecule by selecting for mutant bacteria that are hypersensitive to its inducing activity. The mutant genes identified encode an efflux pump whose proposed activity increases the concentration of the inducer necessary for vir gene expression; this pump is also involved in antibiotic resistance, demonstrating a relationship between cellular defense activities and the control of virulence in Agrobacterium.