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

Abstract

SummaryThe 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.

Ribosome Biogenesis in Plants: From Functional 45S Ribosomal DNA Organization to Ribosome Assembly Factors

“…Moreover, 45S rRNA genes are overexpressed in plants with reduced FK506 BINDING PROTEIN (FKBP53) gene expression (Li and Luan, 2010). In addition, the 3xHMG-box1 (HIGH MOBILITY GROUP) protein binds to 45S rDNA loci via its basic N-terminal domain (Antosch et al, 2015). It is not known whether 3xHMG-box1 is related to Upstream Binding Protein (UBF) and/or High Mobility1(Hmo1), two HMG proteins involved in rDNA transcription in animal and yeast cells, respectively (Sanij et al, 2008;Albert et al, 2013).…”

Critical Role of Transcript Cleavage in Arabidopsis RNA Polymerase II Transcriptional Elongation

“…After sowing, seeds were stratified in darkness for 48h at 4°C prior to incubation in a plant incubator (Percival Scientific). Agrobacteriummediated transformation of Col-0 or tfIIs plants and characterisation of obtained transgenic lines was performed as previously described (Antosch et al, 2015;Dürr et al, 2014). Plant phenotypes including root growth in the presence of β-estradiol were documented as described (Dürr et al, 2014;Lolas et al, 2010).…”

“…Whole protein extracts from PSD-B cultures were prepared using the procedure described above, whereas the whole protein extracts from Arabidopsis seedlings were prepared as described (Tsugama et al, 2011). After separation by SDS-PAGE, proteins were electrotransferred onto PVDF membrane and detected by chemiluminescence (Antosch et al, 2015;Antosz et al, 2017).…”

Transcriptomic analysis under ethylene precursor treatment uncovers the regulation of gene expression linked to sexual reproduction in the dioecious red alga Pyropia pseudolinearis

“…The Arabidopsis genome encodes two family members, termed 3xHMG-box1 and 3xHMG-box2. The transcription of 3xHMG-box1/2 genes is coupled with cell proliferation and the association of 3xHMG-box2 with mitotic chromosomes suggests that they play a role in the organization of mitotic chromosomes, while transcription of the 3xHMG-box1 is detected specifically at the 45S rDNA loci (Antosch et al 2015;Pedersen et al 2011). Interestingly, we found genes encoding 3xHMG-box proteins in red algae genomes such as those of P. umbilicalis (a bangiophyte) (Brawley et al 2017) and Gracilariopsis chorda (a florideophyte) (Lee et al 2018).…”