Chromatin remodelling during plant-pathogen interactions

Abstract

Plants - including commercially important crops - are exposed to numerous pathogens often resulting in significant loss of yield. Understanding the underlying mechanisms of pathogen recognition and defence strategies is key in successfully ensuring food security. Research on plant-pathogen interactions has mainly focused on the gene networks after pathogen perception as well the identification of resistance genes. Latest research suggests that chromatin remodelling, including nucleosome displacement and DNA or histone-modifying enzymes are important in plant immunity. This thesis focuses on chromatin remodelling as the mechanism by which plants mount an effective immune response. The thesis also investigates the role of histone acetylation as one of several chromatin remodelling mechanisms. Histone acetyltransferases (HATs) and histone deacetylases (HDACs) are two classes of histone modifying enzymes that antagonistically govern the acetylation levels of histones in gene promoters and gene bodies ultimately affecting gene expression. HAG1 was identified as an important positive regulator of plant immunity in the interaction with Pst DC3000. A proteomic approach allowed the identification of TOPLESS family members as HAG1 interactors. Considering that chromatin remodelling is an important aspect of plant immunity, it was hypothesised that pathogens have evolved mechanisms to interfere with such processes. To this end, this thesis will present a comprehensive approach towards identifying Pst DC3000 Type-III effectors with the ability to interfere with chromatin remodelling. HopO1-1 was initially identified as an effector with chromatin binding properties, however, further experiments pointed more strongly towards this effector’s involvement in processes such as translation and photosynthesis. Overall, this thesis contributes towards a better understanding of the roles of histone acetylation and HAG1 histone acetyltransferase in plant immunity and sheds light into which Pst DC3000 effectors could be potentially involved in chromatin remodelling processes