Abstract
The SMC 5/6 complex together with cohesin and condensin is a member of the structural maintenance of chromosome (SMC) protein family. In non-plant organisms SMC5/6 is engaged in DNA repair, meiotic synapsis, genome organization and stability. In plants, the function of SMC5/6 is still enigmatic. Therefore, we analyzed the crucial δ-kleisin component NSE4 of the SMC5/6 complex in the model plant Arabidopsis thaliana. Two functional conserved Nse4 paralogs (Nse4A and Nse4B) are present in A. thaliana, which may have evolved via gene subfunctionalization. Due to its high expression level, Nse4A seems to be the more essential gene, whereas Nse4B appears to be involved mainly in seed development. The morphological characterization of A. thaliana T-DNA mutants suggests that the NSE4 proteins are essential for plant growth and fertility. Detailed investigations in wild-type and the mutants based on live cell imaging of transgenic GFP lines, fluorescence in situ hybridization (FISH), immunolabeling and super-resolution microscopy suggest that NSE4A acts in several processes during plant development, such as mitosis, meiosis and chromatin organization of differentiated nuclei, and that NSE4A operates in a cell cycle-dependent manner. Differential response of NSE4A and NSE4B mutants after induced DNA double strand breaks (DSBs) suggests their involvement in DNA repair processes.
Highlights
The evolutionarily conserved structural maintenance of chromosome (SMC) protein complexes are ubiquitous across different organisms from bacteria to humans, and act in basic biological processes such as sister chromatid cohesion, chromosome condensation, transcription, replication, DNA repair and recombination
Via applying live cell imaging, fluorescence in situ hybridization (FISH), immunolabeling and superresolution microscopy, we found that especially NSE4 proteins show similar lengths (NSE4A) proteins act in transcriptionally active somatic interphase chromatin and that they are essential for proper mitosis and meiosis
NSE4A shows a relatively high amino acid similarity compared to both B. rapa putative NSE4 proteins (Supplementary Figure S3), and other plant species (Supplementary Figure S4A)
Summary
The evolutionarily conserved structural maintenance of chromosome (SMC) protein complexes are ubiquitous across different organisms from bacteria to humans, and act in basic biological processes such as sister chromatid cohesion, chromosome condensation, transcription, replication, DNA repair and recombination. The SMC proteins realize these many different functions via ATP-stimulated DNA-bridging to perform intra- and intermolecular linking. It has been proposed that a bacterial or archaea SMC is the forerunner of all eukaryotic SMC complexes. Due to its interactions with the conserved kite (kleisin-interacting tandem winged-helix elements) proteins the SMC5/6 complex is regarded to represent the closest eukaryotic relative to the common SMC ancestor compared to cohesin and condensin (Palecek and Gruber, 2015)
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