RT Journal Article SR Electronic T1 Photoreceptor Regulation of CONSTANS Protein in Photoperiodic Flowering JF Science JO Science FD American Association for the Advancement of Science SP 1003 OP 1006 DO 10.1126/science.1091761 VO 303 IS 5660 A1 Valverde, Federico A1 Mouradov, Aidyn A1 Soppe, Wim A1 Ravenscroft, Dean A1 Samach, Alon A1 Coupland, George YR 2004 UL http://science.sciencemag.org/content/303/5660/1003.abstract AB Many plants flower in response to seasonal fluctuations in day length. The CONSTANS (CO) gene of Arabidopsis promotes flowering in long days. Flowering is induced when CO messenger RNA expression coincides with the exposure of plants to light. However, how this promotes CO activity is unknown. We show that light stabilizes nuclear CO protein in the evening, whereas in the morning or in darkness the protein is degraded by the proteasome. Photoreceptors regulate CO stability and act antagonistically to generate daily rhythms in CO abundance. This layer of regulation refines the circadian rhythm in CO messenger RNA and is central to the mechanism by which day length controls flowering.