Erwinia amylovora is a plant pathogenic bacterium that causes the disease fire blight in a wide range of Rosaceous plants including apples and pears. This pathogen utilizes the hypersensitive response and pathogenicity (hrp)-type III secretion system (T3SS), an essential pathogenicity factor of E. amylovora, to deliver proteins from bacteria to plant apoplasts or the cytoplasm to regulate host immune responses and physiology. Proteins secreted by the E. amylovora T3SS include five effectors: DspA/E, Eop1, Eop3, Eop4 (AvrRpt2Ea), and HopPtoCEa, two harpins: HrpN and HrpW, and other proteins such as Eop2, HrpJ, and HrpK. Homologs of these T3SS-secreted proteins have been characterized in plant pathogens like Pseudomonas syringae, Xanthomonas spp., Ralstonia spp., plant symbionts like Rhizobium spp. and animal pathogens such as Yersinia spp., implicating a central role of these effector proteins in manipulating bacterial interactions with diverse host species. Translocation of effectors is crucial for T3SS-mediated disease development in hosts. It is thought to be mediated by cognate chaperones, but the translocation of E. amylovora DspA/E was recently shown to be regulated by several different chaperones as well as a previously reported harpin, HrpN, in addition to its cognate chaperone DspB/F. This suggests that the dynamics of effector translocation are more complicated than previously expected in E. amylovora. In this review, we summarize the current knowledge of E. amylovora T3SS effectors, chaperones, and harpins together with their homologs from other plant-associated bacterial species. We also discuss the roles of T3SS-secreted proteins in pathogenicity and fitness via exploring their localization, activity, and direct or indirect targets in host plants. Finally, we provide future perspectives on studying effector biology and the T3SS in E. amylovora and how this fundamental knowledge provides potential applications in preventing fire blight.

中文翻译：

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火疫病病原体梨火疫病菌中 III 型分泌系统的效应物、伴侣和 harpins：综述

Erwinia amylovora 是一种植物病原菌，可在包括苹果和梨在内的多种蔷薇科植物中引起火疫病。这种病原体利用过敏反应和致病性 (hrp)-III 型分泌系统 (T3SS)，这是梨火疫病菌的重要致病因子，将蛋白质从细菌传递到植物质外体或细胞质，以调节宿主免疫反应和生理机能。E. amylovora T3SS 分泌的蛋白质包括五个效应子：DspA/E、Eop1、Eop3、Eop4 (AvrRpt2Ea) 和 HopPtoCEa，两个 harpins：HrpN 和 HrpW，以及其他蛋白质，如 Eop2、HrpJ 和 HrpK。这些 T3SS 分泌蛋白的同源物已在植物病原体如丁香假单胞菌、黄单胞菌属、雷氏菌属、植物共生体如根瘤菌属中表征。和动物病原体，如耶尔森氏菌属，暗示这些效应蛋白在操纵细菌与不同宿主物种的相互作用中的核心作用。效应子的易位对于宿主中 T3SS 介导的疾病发展至关重要。它被认为是由同源伴侣介导的，但最近表明，除了其同源伴侣 DspB/F 之外，梨火疫病菌 DspA/E 的易位还受几种不同的伴侣以及先前报道的 harpin HrpN 的调节。这表明效应子易位的动力学比以前在 E. amylovora 中预期的更复杂。在这篇综述中，我们总结了目前关于梨火疫病菌 T3SS 效应器、分子伴侣和 harpins 的知识以及它们来自其他植物相关细菌物种的同源物。我们还通过探索 T3SS 分泌蛋白在宿主植物中的定位、活性以及直接或间接目标，讨论了它们在致病性和适应性中的作用。最后，我们提供了研究梨火疫病菌中效应生物学和 T3SS 的未来观点，以及这些基础知识如何在预防火疫病方面提供潜在应用。