Abstract
The circadian clock is the biological timekeeping system that governs the approximately 24-h rhythms of genetic, metabolic, physiological and behavioral processes in most organisms. This oscillation allows organisms to anticipate and adapt to day–night changes in the environment. Molecular studies have indicated that a transcription–translation feedback loop (TTFL), consisting of transcriptional repressors and activators, is essential for clock function in Arabidopsis thaliana (Arabidopsis). Omics studies using next-generation sequencers have further revealed that transcription factors in the TTFL directly regulate key genes implicated in clock-output pathways. In this review, the target genes of the Arabidopsis clock-associated transcription factors are summarized. The Arabidopsis clock transcriptional network is partly conserved among angiosperms. In addition, the clock-dependent transcriptional network structure is discussed in the context of plant behaviors for adapting to day–night cycles.
Highlights
Circadian regulation of biological processes is thought to be crucial for prediction and adaptation to day–night cycles
TCP21, known as CCA1-HIKING EXPEDITION (CHE), represses CCA1 [42]. This highly wired genetic network in which the expression of clock-associated genes is modulated by internal and external signals increases the variation in expression timing, a feature that may contribute to the ability of plants to adapt to environmental changes that originate from day–night cycles [10,43,44,45]
Genetic studies have indicated that CCA1 and LATE ELONGATED HYPOCOTYL (LHY) are essential for the clock and influence output biological processes such as hypocotyl elongation, flowering time, cold-stress responses and photosynthesis [11,46,47,48,49]
Summary
Circadian regulation of biological processes is thought to be crucial for prediction and adaptation to day–night cycles. Meta-analysis of these transcriptome analyses showed that expression of about 90% of genes is cyclic at least in one diel or under circadian conditions [19] By mining these transcriptome data, some biological processes under clock control were found. CCA1 and LHY repress the transcription of clock-associated genes expressed from morning to evening. TCP21, known as CCA1-HIKING EXPEDITION (CHE), represses CCA1 [42] This highly wired genetic network in which the expression of clock-associated genes is modulated by internal and external signals increases the variation in expression timing, a feature that may contribute to the ability of plants to adapt to environmental changes that originate from day–night cycles [10,43,44,45]
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