Assembly and possible functions of heterochromatin in Arabidopsis thaliana - The role of DNA methylation and histone modifications

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Chromocentres are the hererochromatic compartments of the interphase nucleus. In Arabidopsis nuclei, they are visible as conspicious, individual structures, each containing one or more (peri)centromeric chromosome regions. This ordered pattern greatly facilitates the study of chromosome organization during interphase. This project focuses on the relationship between DNA sequence, heterochromatin formation and gene expression in plant nuclei. Based on FISH studies with interphase nuclei of Arabidopsis a model for the organization of a chromosome during interphase is proposed, in which the centromere region and other heterochromatic segments are located in the chromocentre, while the euchromatic segments are clustered as chromatin loops around this centre. This model will be tested. Chromosome- and (peri)centromere-specific DNA probes from distinct chromosomal regions, and (hetero)chromatin specific antibodies, will be used to analyse the composition and organization of heterochromatin and euchromatin in different stages of interphase. Transgenic and mutant Arabidopsis plants, which are likely affected in their chromatin organization, will be compared with the wild type. In conjunction with the genetic and molecular potential of Arabidopsis, this cytological approach will provide important isight into the epigenetic mechanism of gene regulation.