Temporal orchestration of PRRs fine-tunes circadian pacing and anticipates environmental cues

The five pseudo-response regulators (PRRs) in Arabidopsis are key transcriptional repressors in regulating the circadian clock, yet the mechanisms by which they cooperate to maintain circadian homeostasis and adapt to environmental changes remains unclear. We show that PRR9, PRR5, and TOC1 have interchangeable roles in determining circadian pace through promoter swapping and chromatin immunoprecipitation assays. PRRs form homodimers and heterodimers with sequential rhythms lasting approximately 12 h, with the pseudo-receiver (PR), ethylene-responsive element-binding factor-associated amphiphilic repression motif (EAR), and C-terminal CONSTANS, CONSTANS-like, and TOC1 motif (CCT) domains being essential for dimer formation. These interactions coincide with extended periods of high protein abundance and are essential for sustaining the 24-h circadian oscillation. Based on these dynamics, we propose a "PRR escapement" model that explains the diverse circadian periods of prr mutants. Additionally, PRRs rapidly respond to environmental cues, such as light and temperature, adjusting transcription and protein-complex assembly to align growth with environmental changes.