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

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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.