Mechanismen der Genregulation bei der 'geprimten' Stressantwort in Arabidopsis thaliana

Abstract

During evolution, plants developed various defense mechanisms against pathogens. One of these mechanisms is called systemic acquired resistance (SAR). SAR confers protection to a broad spectrum of pathogen and also to abiotic stress. SAR is associated with the expression of genes encoding pathogenesis–related proteins and with a process called “defense priming”. “Defense priming” enables the plant to respond to pathogen infection or abiotic stresses in a faster and stronger manner. It is assumed that defense priming is an important part of plant disease resistance and stress tolerance. One type of reaction that gets induced in a faster and more robust manner in primed plants is the induction of defense genes. Gene induction can be regulated in different ways. It is known that, amongst others, transcription factors and histones are important for gene regulation. Histones can be modified thereby controlling the accessibility of regulatory proteins to DNA and chromatin. Amongst the regulatory proteins are transcription factors. These proteins bind to regulatory DNA sequences or to chromatin and subsequent recruit proteins that are necessary for gene induction. In this work histone modifications on the promoters of “primed” genes were investigated. The results show that priming and SAR are associated with an increase of certain histone modifications on defense genes. The investigated genes belong to two different groups. On genes of the one group, – which encode so called WRKY transcription factors – an increase of normally transcription-associated histone modifications was observed. This observation suggests that the WRKY transcription factor genes become prepared (primed) for gene induction. The other group of genes encodes enzymes of the phenylpropanoid pathway and also shows changes in histone modifications. But, according to current knowledge no task can be assigned to these changes. Further experiments determined the role of heat shock transcription factor B1 (HSFB1), a transcription factor that is necessary for defense priming. It could be demonstrated that a mutation of the HSFB1 gene neither affects perception of a pathogen nor the systemic transmission of the SAR inducing signal(s). Although it was not possible to exactly determine the role of HSFB1 in priming, I could show that HSFB1 is a priming specific transcription factor