Mitotic lifecycle of chromosomal 3xHMG-box proteins and the role of their N-terminal domain in the association with rDNA loci and proteolysis

作者：Antosch Martin; Schubert Veit; Holzinger Philipp; Houben Andreas; Grasser Klaus D^*

来源：NEW PHYTOLOGIST, 2015, 208(4): 1067-1077.

DOI：10.1111/nph.13575

• Arabidopsis
• chromatin
• high mobility group (HMG)-box domain
• HMGB
• mitotic chromosome
• rDNA
• selective proteolysis

The high mobility group (HMG)-box is a DNA-binding domain characteristic of various eukaryotic DNA- binding proteins. 3xHMG-box proteins (containing three copies of the HMG-box domain and a unique basic N-terminal domain) are specific for plants and the Arabidopsis genome encodes two versions termed 3xHMG-box1 and 3xHMG-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 Arabidopsis thaliana 3xHMG-box proteins.
Live cell imaging and structured illumination microscopy revealed that the expression of the 3xHMG-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. 3xHMG-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 3xHMG-box proteins are degraded and an N-terminal destruction-box mediates the proteolysis. Ectopic expression/localisation of 3xHMG-box1 in interphase nuclei results in reduced plant growth and various developmental defects including early bolting and abnormal flower morphology.
The remarkable conservation of 3xHMG-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.

• 出版日期2015-12