Chromatin modifications associated with priming and activation of defense-related genes in Arabidopsis thaliana

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After initial contact with a necrotizing pathogen, plants can acquire resistance to further pathogen attack in both the infected and the non-infected tissue. This type of enhanced disease resistance is called “systemic acquired resistance” (SAR). SAR is associated with a sensitization (“priming”) of the promoters of certain defense-related (DR) genes. Consequently, the corresponding transcripts accumulate faster and to higher levels in plants with SAR as compared to plants without SAR. This project aims to elucidate how the information about primary pathogen attack is realized at the level of DR gene promoters. Recent studies suggested that the chromatin structure which is determined, amongst others, by covalent modification of histones, is controlling the transcriptional state of a gene and is capable of constituting a cellular memory of previous events. We teamed up to bring together phytopathology and chromatin competence to study chromatin modifications during the establishment of priming and promoter activation of representative DR genes. The PAL-1 and PAL-2 genes of Arabidopsis thaliana will be analyzed for changes in histone acetylation and methylation as well as nucleosome density. We will compare the basal activity state, the primed state, and the activated state of the genes. Furthermore, we will compare chromatin modifications associated with the inactivated and activated states of the PR-1 gene in a time-course experiment. The recorded pattern of chromatin modifications will be investigated in mutants and overexpresser lines affected in either DR transcript accumulation or histone modification. The results will provide novel insights into both the establishment of SAR and the histone code of DR genes in plants.