Condensation of SEUSS promotes hyperosmotic stress tolerance in Arabidopsis.

Osmotic stress imposed by drought and high salinity inhibits plant growth and crop yield. However, our current knowledge on the mechanism by which plants sense osmotic stress is still limited. Here, we identify the transcriptional regulator SEUSS (SEU) as a key player in hyperosmotic stress response in Arabidopsis. SEU rapidly coalesces into liquid-like nuclear condensates when extracellular osmolarity increases. The intrinsically disordered region 1 (IDR1) of SEU is responsible for its condensation. IDR1 undergoes conformational changes to adopt more compact states after an increase in molecular crowding both in vitro and in cells, and two predicted α-helical peptides are required. SEU condensation is indispensable for osmotic stress tolerance, and loss of SEU dramatically compromises the expression of stress tolerance genes. Our work uncovers a critical role of biomolecular condensates in cellular stress perception and response and expands our understanding of the osmotic stress pathway.