SOSEKI proteins (SOK1-5) locally interpret global polarity cues and can influence cell division orientation to coordinate cell polarization relative to body axes, probably by guiding ANGUSTIFOLIA (AN) polarized localization. Homodimer (By similarity). Forms long polymer filaments with other SOKs proteins polymers (e.g. SOK1, SOK2, SOK3 and SOK4) crucial for polar localization and biological activity (PubMed:32004461). Binds to ANGUSTIFOLIA (AN) (PubMed:32004461). SOSEKI proteins integrate apical-basal and radial organismal axes to localize to polar cell edges. Expressed during embryogenesis and in roots. Accumulates at the basal side and all corners of most cells in the primary root, lateral roots and embryos. The DIX-like oligomerization domain is required for polymerization, edge localization and biological activity. 'Soseki' means cornerstone in Japanese. Belongs to the SOSEKI family.