Table 1_Pseudomonas cold shock proteins suppress bacterial effector translocation in Nicotiana benthamiana.xlsx

IntroductionPlants detect the invasion of microbial pathogens through pathogen-associated molecular patterns (PAMPs). Cold shock proteins (CSPs) are a class of PAMPs specifically recognized by Solanales plants. While peptide inoculation studies have revealed the effects of CSPs, their in vivo roles remain poorly understood.
MethodsA model system involving the interactions between Pseudomonas fluorescens and P. syringae pv. tomato DC3000 with Nicotiana benthamiana has been widely used to investigate the molecular mechanism of plant-microbe interactions. Here, we employed this model system to explore the in vivo roles of CSPs in modulating plant immunity by multiple genetic approaches.
ResultsOur findings revealed that three highly-conserved CSPs were identified in Pseudomonas strains. Transient expression of these CSPs neither induced reactive oxygen species (ROS) production nor suppressed the hypersensitive response (HR) in N. benthamiana, however, it restricted bacterial effector translocation. Genetic analysis revealed that these CSPs did not contribute to the ROS burst or HR inhibition in vivo but were functionally redundant in suppressing effector translocation in a flagellin (FliC)-independent manner. Furthermore, we demonstrated that the suppression of effector translocation mediated by CSPs was less pronounced compared to that triggered by FliC. Additionally, inoculation with csp15 and csp22 epitopes triggered the pattern-triggered immunity-associated suppression of effector translocations.
DiscussionThis study revealed the redundant roles of CSPs in suppressing bacterial effector translocation in vivo, providing deep insights into the PTI elicited by cytoplasmic bacterial proteins.

引言
植物通过病原相关分子模式（pathogen-associated molecular patterns, PAMPs）识别微生物病原菌的侵染。冷休克蛋白（cold shock proteins, CSPs）是一类被茄目（Solanales）植物特异性识别的PAMPs。尽管肽接种研究已揭示了CSPs的部分功能，但目前对其体内作用的认知仍较为匮乏。

材料与方法
以荧光假单胞菌（Pseudomonas fluorescens）、丁香假单胞菌番茄致病变种DC3000（Pseudomonas syringae pv. tomato DC3000）与本氏烟（Nicotiana benthamiana）的互作为核心的模型系统，已被广泛应用于植物-微生物互作的分子机制研究。本研究借助该模型系统，通过多种遗传学手段探究CSPs在调控植物免疫过程中的体内作用。

结果
本研究在假单胞菌菌株中鉴定出3个高度保守的CSPs。在本氏烟中瞬时表达这些CSPs，既不会诱导活性氧（reactive oxygen species, ROS）产生，也不会抑制过敏反应（hypersensitive response, HR），但可限制细菌效应蛋白的转运。遗传学分析表明，这些CSPs在体内并不参与ROS爆发或HR的抑制，但它们以不依赖鞭毛蛋白（flagellin, FliC）的方式在抑制效应蛋白转运方面存在功能冗余。此外，本研究证实，相较于FliC介导的效应蛋白转运抑制，CSPs介导的该抑制作用效果较弱。另外，接种csp15与csp22表位可触发模式触发免疫（pattern-triggered immunity, PTI）相关的效应蛋白转运抑制过程。

讨论
本研究揭示了CSPs在体内抑制细菌效应蛋白转运的冗余功能，为理解胞质细菌蛋白引发的PTI提供了深刻的理论见解。