Sci Adv. 2026 Oct 16. 12(42):
eaei1213
The circadian clock enhances plant fitness by aligning internal timing with the external photoperiod, but how it coordinates spatiotemporal regulation with chromatin dynamics to improve salt tolerance is not well understood. Here, we show that the clock component TIME FOR COFFEE (TIC) forms biomolecular condensates in response to salt stress, but not to osmotic stress alone. Consistently, tic mutants were hypersensitive to salt stress yet displayed enhanced salt tolerance under 21-hour light-dark cycles matching their shortened circadian period, highlighting the importance of circadian clock in salt tolerance. Salt stress increases H3K9ac levels at the salt stress-responsive genes and induces their expression in a time-of-day-dependent manner in wild-type plants, whereas both H3K9ac level and transcriptional activation are attenuated in tic mutants. TIC physically associates with HD2-type histone deacetylases, and a subset of HD2 partially colocalizes with TIC condensates in the nucleolus under salt stress. Genetic and biochemical analyses showed that salt stress promotes TIC condensate formation, accompanied by reduced HD2 occupancy at salt stress-responsive loci, thereby elevating H3K9ac levels and promoting gene expression. Together, these findings uncover a mechanism by which salt-induced TIC condensate formation links chromatin regulation with circadian timing, thereby promoting plant adaptation to salt stress.