Intrinsically disordered proteins as thermosensors in plant

Intrinsically disordered proteins (IDPs) lack stable tertiary structures, allowing them to
change shape and function under different physiological conditions. This flexibility can be highly
advantageous for plants, which often use environmental changes to trigger developmental events
like flowering. For instance, some plants use winter exposure to cue spring flowering. Many genes
involved in temperature-dependent flowering have been studied in Arabidopsis thaliana, yet how
plants perceive temperature changes remains poorly understood. Here, we explore the role of
temperature-sensitive phase separation of the IDP and flowering-time regulator SUPPRESSOR
OF FRIGIDA 4 (SUF4) in regulating flowering. SUF4 plays a key role in temperature-dependent
flowering by activating the floral suppressor FLOWERING LOCUS C (FLC). We found that at low
temperatures (4°C), SUF4 is miscible and dispersed throughout the nucleoplasm, while at warm
temperatures (20°C), SUF4 dynamically forms nuclear condensates, co-condensing with key FLC
regulators, FRIGIDA (FRI) and EARLY FLOWERING 7 (ELF7). Furthermore, SUF4's disordered
region is critical for condensate formation and flowering regulation. Plants expressing SUF4
variants with graded aromatic/hydrophobic-to-hydrophilic substitutions in this region show
corresponding changes in condensate formation, SUF4 binding to the FLC promoter, FLC
expression, and flowering responses. These findings support the hypothesis that SUF4 regulates
FLC transcriptional activation by using temperature-dependent condensation to enhance its
activity, and possibly that of other flowering regulators, at the FLC gene locus.