Activation of plant immunity by components of the type III secretion system from Xanthomonas campestris pv. vesicatoria

植物通过激发基础防御反应来防御细菌病原体，该反应通常在相应的植物受体识别病原体相关分子模式（PAMPs）时被激活。然而，专门的革兰氏阴性细菌病原体通过效应蛋白的作用抑制pamp触发的免疫（PTI）。在许多情况下，效应蛋白通过III型分泌（T3S）系统转运到植物细胞中，该系统在进化上与细菌鞭毛有关。值得注意的是，细胞外鞭毛细丝的主要成分是一种经过充分研究的细菌PAMP。相比之下，与易位相关的T3S系统的组成部分尚未被报道有助于PTI的引发。为了研究易位相关T3S系统的潜在PAMP活性，我们对植物致病菌油菜黄单胞菌pv的突变株进行了感染研究。它们缺乏T3S易位，因此缺乏植物质膜中效应蛋白的预测运输通道。我们的初步研究表明，对寄主植物和非寄主植物（如拟南芥）进行预处理，使其具有translocon-deficient campestris pv。白癜风菌株诱导特异性防御基因的激活，抑制致病性菌株的后续感染。在缺乏细胞外T3S菌毛或完整的T3S系统时，观察到的PTI反应明显减少，这表明T3S系统的细胞外成分或底物起到了PAMPs的作用。该项目的目的是表征X. campestris pv的T3S系统的细胞外成分或底物的PAMP活性。与诱导PTI反应相关的植物基因的鉴定。各种病原体的感染实验将揭示T3S系统相关的PAMP是否对微生物入侵者具有普遍的抗性。通过细菌培养上清和纯化的候选PAMP对PTI的激发进行分析，以鉴定T3S系统相关的PAMP。为了表征诱导的防御反应，我们将测量PTI反应，如活性氧和乙烯的产生、有丝分裂原激活的蛋白激酶的激活、胼胝质沉积到植物细胞壁以及防御基因的诱导。为了鉴定参与PTI对T3S系统相关PAMP响应的植物基因，我们将测试不同拟南芥材料对T3S系统相关PAMP的响应。候选基因将通过定位方法确定，可能在潜在的第二个资助期。综上所述，所提出的实验将有助于表征植物对细菌T3S系统的防御策略，并可能揭示translocons缺陷X. campestris pv的潜在用途。作为一般生物防治剂的发汗菌。

Plants defend themselves against bacterial pathogens by the elicitation of basal defense reactions which are often activated upon recognition of pathogen-associated molecular patterns (PAMPs) by corresponding plant receptors. Specialized Gram-negative bacterial pathogens, however, suppress PAMP-triggered immunity (PTI) by the actions of effector proteins. In many cases, effector proteins are translocated into plant cells by a type III secretion (T3S) system, which is evolutionarily related to the bacterial flagellum. Notably, the main component of the extracellular flagellar filament is a well studied bacterial PAMP. In contrast, components of translocation-associated T3S systems have not yet been reported to contribute to the elicitation of PTI. To investigate a potential PAMP activity of the translocation-associated T3S system, we performed infection studies with mutant strains of the plant-pathogenic bacterium Xanthomonas campestris pv. vesicatoria, which lack the T3S translocon and thus the predicted transport channel for effector proteins in the plant plasma membrane. Our preliminary studies suggest that the pretreatment of host and non-host plants (e.g. Arabidopsis) with translocon-deficient X. campestris pv. vesicatoria strains induces the activation of specific defense genes and suppresses subsequent infections by pathogenic strains. The observed PTI reactions were significantly reduced in the absence of the extracellular T3S pilus or the complete T3S system, suggesting that extracellular components or substrates of the T3S system act as PAMPs. Aim of the proposed project is the characterization of the PAMP activity of extracellular components or substrates of the T3S system from X. campestris pv. vesicatoria and the identification of plant genes which are involved in the induced PTI responses. Infection experiments with various pathogens will reveal whether the T3S system-associated PAMP confers a general resistance against microbial invaders. PTI elicitation by bacterial culture supernatants and purified candidate PAMPs will be analysed to identify the T3S system-associated PAMP. To characterize the induced defense responses, we will measure PTI reactions such as the production of reactive oxygen species and ethylene, the activation of mitogen-activated protein kinases, the deposition of callose into the plant cell wall and the induction of defense genes. For the identification of plant genes, which are involved in the PTI response to the T3S system-associated PAMP, different Arabidopsis accessions will be tested for their responsiveness to the T3S system-associated PAMP. Candidate genes will be identified by mapping approaches, possibly in a potential second funding period. Taken together, the proposed experiments will help to characterize plant defense strategies in response to the bacterial T3S system and might reveal a potential use of translocon-deficient X. campestris pv. vesicatoria strains as general biocontrol agents.