Epigenetic regulation of transcriptional reprogramming in susceptible cells of Arabidopsis in response to Xanthomonas infection

为了对抗由黄单胞菌属病原细菌引起的许多作物的毁灭性疾病，了解宿主植物-病原菌相互作用的分子基础至关重要。与许多其他细菌病原体一样，黄单胞菌通过细菌III型分泌系统将III型效应蛋白的混合物注入宿主细胞。一组效应物被转移到细胞核中，在那里它们抑制参与宿主防御反应的基因，并诱导基因产生有益于疾病的条件。在易感宿主细胞中效应子介导的转录变化的分子机制在很大程度上是未知的。特别是表观遗传调控如何有助于转录重编程迄今为止还没有分析，主要是因为分离靶向效应子的易感细胞用于表观基因组分析的技术挑战。在这个及时的项目中，我将开发新的方法，结合最先进的分子技术和计算工具，使用模式宿主植物拟南芥和细菌病原体黄单胞菌，在表观遗传水平上研究促进疾病的微生物效应子。我将建立一个宿主植物-病原体报告系统，其中生物素化的核靶向蛋白在易感细胞中的表达是由病原体递送的TAL效应物诱导的，从而通过INTACT（分离标记在特定细胞类型中的细胞核）技术促进效应物靶向细胞核的亲和纯化。使用INTACT纯化的细胞核，我将通过高通量测序方法研究细菌效应子诱导的转录和表观遗传标记变化。本项目将通过对黄单胞菌效应子XopD的结构和功能的初步研究，阐明其功能。我们将阐明XopD靶向宿主染色质并通过表观遗传转录抑制机制调控靶基因表达的假设，这不仅有助于我们从总体上理解黄单胞菌的分子致病机理，而且将推进植物病理学研究领域的方法学。这些成果最终将有助于防治作物中的细菌性疾病，实现可持续农业。

In order to combat the devastating disease of many crops caused by Xanthomonas pathogenic bacterial species, it is crucial to understand the molecular basis of the host plant-pathogen interaction. Like many other bacterial pathogens, Xanthomonas injects a cocktail of Type III effector proteins via the bacterial type III secretion system into the host cells. A group of effectors are translocated into the nucleus where they repress the genes involved in host defense responses and induce the genes for generating beneficial conditions for the disease. The molecular mechanisms of effector-mediated transcriptional changes in susceptible host cells are largely unknown. Particularly how epigenetic regulation contributes to the transcription reprogramming has eluded analysis so far, mostly because of the technical challenges of isolating effector-targeted susceptible cells for epigenomic analyses. In this timely project, I will develop novel approaches in combination of state-of-the-art molecular techniques and computational tools, to study microbial effectors that promote disease at the epigenetic level, using the model host plant Arabidopsis and the bacterial pathogen Xanthomonas. I will establish a host plant-pathogen reporter system, where expression of a biotinylated nuclear envelope-targeting protein in susceptible cells is induced by pathogen-delivered TAL effector, facilitating affinity purification of effector-targeted nuclei by the INTACT (isolation of nuclei tagged in specific cell types) technology. Using INTACT-purified nuclei, I will investigate bacterial effector-induced changes in transcription and epigenetic marking by high-throughput sequencing approaches. This project will focus on the functional elucidation of the Xanthomonas effector XopD based on its structure and preliminary studies. We will address the hypothesis that XopD targets host chromatin and regulates target gene expression through epigenetic transcriptional repression mechanisms.My results will not only contribute to our understanding of molecular pathogenesis of Xanthomonas in general, but will also advance the methodology in the research field of plant pathology. The outcomes will ultimately contribute to combat the bacterial disease in crops and achieve a sustainable agriculture.