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

为了防治由黄单胞菌病原菌引起的多种作物病害，了解寄主植物与病原菌相互作用的分子基础至关重要。像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射到宿主细胞中。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，并诱导基因产生对疾病有益的条件。在易感宿主细胞中，效应物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促进转录重编程，迄今为止还没有得到分析，主要是因为分离效应靶易感细胞进行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，研究在表观遗传水平上促进疾病的微生物效应，使用模式寄主植物拟南芥和细菌病原体黄单胞菌。我将建立一个寄主植物-病原体报告系统，在该系统中，病原体递送的TAL效应物诱导易感细胞中生物素化核膜靶向蛋白的表达，促进效应物靶向细胞核的亲和纯化，通过integrity（分离特定细胞类型标记的细胞核）技术。使用完整纯化的细胞核，我将通过高通量测序方法研究细菌效应诱导的转录和表观遗传标记的变化。本项目将在黄单胞菌效应物XopD的结构和初步研究的基础上，重点对其功能进行阐述。我们将解决XopD靶向宿主染色质并通过表观遗传转录抑制机制调节靶基因表达的假设。我的研究结果不仅有助于我们对黄单胞菌的分子发病机制的全面认识，而且将推动植物病理学研究领域的方法学发展。研究成果最终将有助于防治作物细菌性病害，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.