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Mitotic lifecycle of chromosomal 3x HMG ‐box proteins and the role of their N‐terminal domain in the association with r DNA loci and proteolysis

2015; Wiley; Volume: 208; Issue: 4 Linguagem: Inglês

10.1111/nph.13575

1469-8137

Martin Antosch, Veit Schubert, Philipp Holzinger, Andreas Houben, Klaus D. Grasser,

Plant Molecular Biology Research

Summary The high mobility group ( HMG )‐box is a DNA ‐binding domain characteristic of various eukaryotic DNA ‐binding proteins. 3x HMG ‐box proteins (containing three copies of the HMG ‐box domain and a unique basic N‐terminal domain) are specific for plants and the A rabidopsis genome encodes two versions termed 3x HMG ‐box1 and 3x HMG ‐box2, whose expression is cell cycle‐dependent, peaking during mitosis. Here, we analysed in detail the spatiotemporal expression, subcellular localisation and chromosome association of the A rabidopsis thaliana 3x HMG ‐box proteins. Live cell imaging and structured illumination microscopy revealed that the expression of the 3x HMG ‐box proteins is induced in late G2 phase of the cell cycle and upon nuclear envelope breakdown in prophase they rapidly associate with the chromosomes. 3x HMG ‐box1 associates preferentially with 45S rDNA loci and the basic N‐terminal domain is involved in the targeting of rDNA loci. Shortly after mitosis the 3x HMG ‐box proteins are degraded and an N‐terminal destruction‐box mediates the proteolysis. Ectopic expression/localisation of 3x HMG ‐box1 in interphase nuclei results in reduced plant growth and various developmental defects including early bolting and abnormal flower morphology. The remarkable conservation of 3x HMG ‐box proteins within the plant kingdom, their characteristic expression during mitosis, and their striking association with chromosomes, suggest that they play a role in the organisation of plant mitotic chromosomes.