Physcomitrium patens SUN2 Mediates MTOC Association with the Nuclear Envelope and Facilitates Chromosome Alignment during Spindle Assembly.

This article investigates the role of the inner nuclear membrane protein SUN2 in the moss Physcomitrium patens, focusing on its function in positioning acentrosomal microtubule organizing centers (MTOCs) at the nuclear envelope (NE) during mitotic prophase. The study demonstrates that SUN2 is essential for proper MTOC localization, microtubule accumulation around the NE, and efficient chromosome alignment during spindle assembly, with sun2 knockout cells exhibiting mislocalized MTOCs, delayed mitosis, and impaired nuclear morphology. SUN2 shows asymmetric localization dependent on microtubules, suggesting a conserved role in linking microtubules to the nucleus similar to the LINC complex function in animals and yeast. Additionally, SUN2 influences MTOC positioning and spindle orientation in gametophore initial cells, indicating its broader involvement in nuclear–cytoskeletal interactions in plant cell division.