Central component of cohesin, a complex required for chromosome cohesion during the cell cycle. The cohesin complex may form a large proteinaceous ring within which sister chromatids can be trapped. At anaphase, the complex is cleaved and dissociates from chromatin, allowing sister chromatids to segregate. Cohesion is coupled to DNA replication and is involved in DNA repair. The cohesin complex also plays an important role in spindle pole assembly during mitosis and in chromosomes movement (By similarity). Essential protein plant viability. Required for chromosome segregation (e.g. sister chromatid alignment) and cell division during embryogenesis. Cohesin complexes are composed of the SMC1 and SMC3 heterodimer attached via their SMC hinge domain, SCC3, and an alpha-kleisin subunit SCC1 linked to one SYN subunit (SYN1, SYN2, SYN3 or SYN4). Associates with chromatin. Mostly expressed in flower buds and stems, and, to a lower extent, in leaves and roots. The flexible SMC hinge domain, which separates the large intramolecular coiled coil regions, allows the heterotypic interaction with the corresponding domain of SMC1A or SMC1B, forming a V-shaped heterodimer. The two heads of the heterodimer are then connected by different ends of the cleavable RAD21 protein, forming a ring structure (By similarity). Altered chromosome dynamics and cell division during seed development, leading to aberrant mitoses and giant polyploid nuclei in endosperm as well as arrested embryos with a few small cells. Belongs to the SMC family. SMC1 subfamily.