Absence of SUN1 and SUN2 proteins in Arabidopsis thaliana leads to a delay in meiotic progression and defects in synapsis and recombination

The movement of chromosomes during meiosis involves location of their telomeres at the inner surface of the nuclear envelope. Sad1/UNC-84 (SUN) domain proteins are inner nuclear envelope proteins that are part of complexes linking cytoskeletal elements with the nucleoskeleton, connecting telomeres to the force-generating mechanism in the cytoplasm. These proteins play a conserved role in chromosome dynamics in eukaryotes. Homologues of SUN domain proteins have been identified in several plant species. In Arabidopsis thaliana, two proteins that interact with each other, named AtSUN1 and AtSUN2, have been identified. Immunolocalization using antibodies against AtSUN1 and AtSUN2 proteins revealed that they were associated with the nuclear envelope during meiotic prophase I. Analysis of the double mutant Atsun1-1 Atsun2-2 has revealed severe meiotic defects, namely a delay in the progression of meiosis, absence of full synapsis, the presence of unresolved interlock-like structures, and a reduction in the mean cell chiasma frequency. We propose that in Arabidopsis thaliana, overlapping functions of SUN1 and SUN2 ensure normal meiotic recombination and synapsis.