Arabidopsis NSE4 Proteins Act in Somatic Nuclei and Meiosis to Ensure Plant Viability and Fertility

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 <i>Arabidopsis thaliana</i>. Two functional conserved <i>Nse4</i> paralogs (<i>Nse4A</i> and <i>Nse4B</i>) are present in <i>A. thaliana</i>, which may have evolved via gene subfunctionalization. Due to its high expression level, <i>Nse4A</i> seems to be the more essential gene, whereas <i>Nse4B</i> appears to be involved mainly in seed development. The morphological characterization of <i>A. thaliana</i> 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 <i>in situ</i> 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.