Hyytiäinen Heidi, Sjöblom Solveig, Palomäki Tiina, Tuikkala Anne, Tapio Palva E
Department of Biosciences, Division of Genetics, Box 56, FIN-00014 University of Helsinki, Finland.
Mol Microbiol. 2003 Nov;50(3):795-807. doi: 10.1046/j.1365-2958.2003.03729.x.
Efficient response to environmental cues is crucial to successful infection by plant-pathogenic bacteria such as Erwinia carotovora ssp. carotovora. The expression of the main virulence genes of this pathogen, encoding extracellular enzymes that degrade the plant-cell wall, is subject to complex regulatory machinery where two-component systems play an important role. In this paper, we describe for the first time the involvement of the PmrA-PmrB two-component system in regulation of virulence in a plant-pathogenic bacterium. Disruption of pmrB resulted in reduced virulence both in potato and in Arabidopsis. This is apparently due to reduced production of the extracellular enzymes. In contrast, a pmrA mutant exhibited increased levels of these enzymes implying negative regulation of the corresponding genes by PmrA. Furthermore, the pmrB but not pmrA mutant exhibited highly increased resistance to the cationic antimicrobial peptide polymyxin B suggesting alterations in cell surface properties of the mutant. A similar increase of polymyxin resistance was detected in the wild type at mildly acidic pH with low Mg2+. Functional pmrA is essential for bacterial survival on excess iron at acidic pH, regardless of the Mg2+ concentration. We propose that PmrA-PmrB TCS is involved in controlling of bacterial response to external pH and iron and is crucial for bacterial virulence and survival in planta.
对环境信号的有效响应对于诸如胡萝卜软腐欧文氏菌胡萝卜软腐亚种等植物致病细菌的成功感染至关重要。该病原体的主要毒力基因编码可降解植物细胞壁的胞外酶，其表达受复杂的调控机制控制，其中双组分系统发挥着重要作用。在本文中，我们首次描述了PmrA-PmrB双组分系统参与植物致病细菌毒力的调控。pmrB的破坏导致在马铃薯和拟南芥中的毒力均降低。这显然是由于胞外酶的产生减少所致。相反，pmrA突变体表现出这些酶的水平升高，这意味着PmrA对相应基因具有负调控作用。此外，pmrB突变体而非pmrA突变体对阳离子抗菌肽多粘菌素B表现出高度增强的抗性，这表明突变体的细胞表面特性发生了改变。在轻度酸性pH和低Mg2+条件下，野生型中也检测到多粘菌素抗性的类似增加。无论Mg2+浓度如何，功能性pmrA对于细菌在酸性pH下过量铁存在时的存活至关重要。我们提出，PmrA-PmrB双组分系统参与控制细菌对外部pH和铁的响应，并且对于细菌在植物中的毒力和存活至关重要。
