Illuminating what lies in darkness: Circadian regulation of hypocotyl growth in Arabidopsis via ELF3 recruitment of demethylases

Do you ever get so sleepy at night that you literally can't keep your eyes open, even though you really want to finish watching the show you're hooked on? Those heavy eyelids are the result of your body's circadian clock, which keeps you on a 24-hour cycle of wakefulness and sleep. Plants also rely on their circadian clock to coordinate biological functions, including those that promote the light reactions of photosynthesis only during the day when sunlight is available. The hypocotyl grows primarily during the night, and this, too, is regulated by the circadian clock in Arabidopsis (A. thaliana; Niwa et al. 2009). Circadian clocks are composed of many different proteins, many of which operate in a complex system of overlapping negative feedback loops (Sanchez and Kay 2016). Key players in plants' circadian clocks are phytochrome-interacting factors (PIFs), transcription factors that transduce external light signals received by phytochromes, among other signals, into specific control of gene expression (de Lucas and Prat 2014). PIF4 and PIF5 repress hypocotyl growth during the day, while the evening complex enables hypocotyl growth during the night by repressing PIF4/5 transcription. In new work, Shiyu Tian and colleagues (Tian et al. 2025) seek to elucidate the molecular mechanism by which the evening complex regulates PIF4/5 expression.