• Light perception via phytochromes/cryptochromes shapes clock output and entrainment by regulating transcription of clock-controlled genes and promoter elements; phototransduction modulates circadian period and light responses, with phytochrome/cryptochrome mutants and CAB2 promoter studies illustrating this pathway [1], [2], [10], [11], [7], [16], [13].

• Clock-driven gene expression and circadian gating under environmental and genetic variation, including circadian oscillations of calcium, clock-gated catalase gene expression, and CCR/CAB regulatory dynamics; these show promoter-level regulation and rhythm-based transcription control [4], [5], [6], [9].

• Circadian clock ties to photoperiodic flowering control, integrating clock signals with flowering time regulation and photoperiod responses, via LD gene, flowering time genes, and photoperiodic modulation [17], [8], [3].

• Cross-species and organelle-linked circadian motifs reveal conserved oscillator components, including chloroplast- and algal-encoded gene rhythms and circadian regulation of non-photosynthetic genes, suggesting broad circadian architecture [15], [19], [4], [14].

• Promoter architecture and cis-regulatory control underpin circadian regulation, illustrating how cis-elements and DNA-protein complexes mediate clock-driven transcription of CAB2 and other genes [11], [16], [7], [10].