CCA1

Circadian Clock Associated 1 (CCA1) is a transcription factor of the MYB family in Arabidopsis thaliana. It is a core component of the plant circadian clock and contributes to aligning physiological processes with daily light cycles.

Expression and role: CCA1 is primarily expressed in the morning and is regulated by light. Together with its close homolog LHY (Late Elongated Hypocotyl), CCA1 helps generate robust 24-hour rhythms by repressing the expression of evening-phased clock genes, thereby shaping the timing of downstream processes.

Mechanism: CCA1 and LHY bind to promoters of clock genes and act as transcriptional repressors in the morning. They form part of a core feedback loop that includes PRR genes (for example PRR9, PRR7, PRR5) and TOC1, and are linked to the Evening Complex (ELF3/ELF4/LUX) that promotes evening-phase expression. Light signaling through photoreceptors influences CCA1 activity and stability.

Genetic and physiological effects: Loss-of-function cca1 mutants exhibit changes in circadian period and altered expression patterns; the cca1 lhy double mutant shows severely damped or arrhythmic rhythms under constant conditions. CCA1 also influences processes such as photosynthesis, metabolism, and growth by regulating clock-controlled genes.

In plant chronobiology, CCA1 serves as a widely used morning-clock marker. Reporter lines and mutants have been instrumental in delineating the architecture of the plant circadian system and its integration with environmental cues.