Manipulating condensation of thermo-sensitive SUF4 protein tunes flowering time in Arabidopsis thaliana.

Intrinsically disordered proteins (IDPs) can undergo environmentally responsive phase separation, raising the question of whether organisms use phase behavior to regulate development. Many plants rely on seasonal temperatures to control flowering time. Yet, how plants coordinate their developmental states with temperature is poorly understood. Here, we investigate the role of temperature-sensitive phase separation using the IDP and flowering-time regulator SUPPRESSOR OF FRIGIDA 4 (SUF4). SUF4 plays a well-defined role in seasonal flowering by activating the floral repressor FLOWERING LOCUS C (FLC). We show that at warm temperatures (20°C), SUF4 forms nuclear condensates that co-localize with key flowering regulators (FRIGIDA and EARLY FLOWERING 7 [ELF7]), whereas at 4°C, these condensates disperse into the nucleoplasm. Moreover, progressive alterations to the amino acid composition of SUF4's disordered region lead to corresponding changes in temperature-dependent condensation, SUF4's ability to bind and transcribe FLC, and flowering time. These findings reveal how temperature-sensitive condensation can drive seasonal development in plants.