A characteristic of cell division is the remarkable condensation of the genomic DNA into mitotic (or meiotic) chromosomes. The compaction of the chromosomes is of fundamental importance for faithful chromosome segregation during mitosis and meiosis, and therefore for proper inheritance. In preparatory work, we have started studying a so far uncharacterised family of plant-specific proteins, containing three HMG-box DNAbinding domains, termed 3xHMG-box proteins. Two Arabidopsis 3xHMG-box proteins interact with DNA, but unlike other HMG-box proteins they display cell cycle dependent expression, peaking in cells undergoing mitosis (and meiosis). Both the Arabidopsis 3xHMG-box proteins associate with condensed mitotic/meiotic chromosomes and 3xHMG-box2 generally associates with condensed chromosomes, whereas 3xHMG-box1 displays a clear preference for 45S rDNA loci. Currently, it is unclear which role these proteins play during mitosis/meiosis, and therefore we intend to address this question in this proposed project. Plants with altered expression levels of the two 3xHMG-box proteins will be analysed for possible phenotypic differences (relative to control plants), for effects on chromosome structure/segregation, histone modifications, 45S rDNA activity and cell cycle abnormalities. We also analyse the molecular differences between the two 3xHMG-box proteins and identify proteins interacting with the 3xHMG-box proteins to learn more about their cellular function. In summary, this project will provide insight into the biological role of the 3xHMG-box proteins in cell division.
