The article by Federico Valverde et al. (2004) investigates the regulation of the CONSTANS (CO) protein in photoperiodic flowering in Arabidopsis. CO is a key gene that promotes flowering in long days, and its mRNA abundance is regulated by the circadian clock, accumulating late in the day when plants are exposed to light. The study reveals that CO protein stability is light-dependent, with the protein being stabilized in the evening and degraded by the proteasome in the morning or in darkness. Photoreceptors, particularly cryptochromes and phytochromes, regulate CO stability, acting antagonistically to generate daily rhythms in CO abundance. This regulation refines the circadian rhythm in CO mRNA and is crucial for the mechanism by which day length controls flowering. The findings suggest that the balance between phyB and cryptochromes drives diurnal rhythms in CO protein abundance, ensuring that CO protein accumulates only at the end of a long day, when it can activate the FT gene, promoting flowering.The article by Federico Valverde et al. (2004) investigates the regulation of the CONSTANS (CO) protein in photoperiodic flowering in Arabidopsis. CO is a key gene that promotes flowering in long days, and its mRNA abundance is regulated by the circadian clock, accumulating late in the day when plants are exposed to light. The study reveals that CO protein stability is light-dependent, with the protein being stabilized in the evening and degraded by the proteasome in the morning or in darkness. Photoreceptors, particularly cryptochromes and phytochromes, regulate CO stability, acting antagonistically to generate daily rhythms in CO abundance. This regulation refines the circadian rhythm in CO mRNA and is crucial for the mechanism by which day length controls flowering. The findings suggest that the balance between phyB and cryptochromes drives diurnal rhythms in CO protein abundance, ensuring that CO protein accumulates only at the end of a long day, when it can activate the FT gene, promoting flowering.