CCRG1 Acts as a Downstream Effector of the Clock Proteins CCA1 and LHY to Coordinate Growth, Flowering, and Senescence.

The circadian clock is an endogenous oscillator that generates ~24-h rhythms, enabling plants to anticipate and adapt to daily environmental cycles. E3 ubiquitin ligases are central regulators of protein turnover in signaling pathways, but their roles in the plant circadian system have yet to be fully elucidated. In this study, we find that the transcript of E3 ligase CCRG1 shows diurnal rhythmicity and sustained oscillation under continuous light in Arabidopsis thaliana. Molecular analyses demonstrate that the core clock components LATE ELONGATED HYPOCOTYL (LHY) and CIRCADIAN CLOCK ASSOCIATED 1 (CCA1) directly regulate CCRG1 transcription through promoter binding. The ccrg1 single mutants exhibit an increase in vegetative growth compared with the wild-type plants. The introduction of CCRG1 mutation in the cca1 lhy double mutants significantly suppresses the developmental defects, restoring vegetative biomass and alleviating premature flowering and leaf senescence. Furthermore, CCA1pro::CCRG1 lines in the Col-0 background showed modestly elevated morning CCRG1 expression without an obvious phase shift and exhibited delayed bolting. Together, our findings establish CCRG1 as a transcriptionally regulated ubiquitination node downstream of the morning oscillator, linking core clock regulation to specific developmental outputs and revealing an additional layer of circadian-controlled protein regulation in plants.