PSEUDO RESPONSE REGULATORs stabilize CONSTANS protein to promote flowering in response to day length

• Published in: The EMBO journal 2017-04, Vol.36 (7), p.904-918
• Main Authors: Hayama, Ryosuke, Sarid‐Krebs, Liron, Richter, René, Fernández, Virginia, Jang, Seonghoe, Coupland, George
• Format: Article
• Language: English
• Subjects: Arabidopsis; Arabidopsis - physiology; Arabidopsis - radiation effects; Arabidopsis Proteins - metabolism; circadian clock; CONSTITUTIVE PHOTOMORPHOGENIC 1; DNA-Binding Proteins - metabolism; EMBO30; EMBO31; EMBO44; Flowers - radiation effects; Light; photoperiodic flowering; Proteins; PSEUDO RESPONSE REGULATOR; Transcription factors; Transcription Factors - metabolism
• ISSN: 0261-4189; 1460-2075
• DOI: 10.15252/embj.201693907

Seasonal reproduction in many organisms requires detection of day length. This is achieved by integrating information on the light environment with an internal photoperiodic time‐keeping mechanism. Arabidopsis thaliana promotes flowering in response to long days (LDs), and CONSTANS (CO) transcription factor represents a photoperiodic timer whose stability is higher when plants are exposed to light under LDs. Here, we show that PSEUDO RESPONSE REGULATOR (PRR) proteins directly mediate this stabilization. PRRs interact with and stabilize CO at specific times during the day, thereby mediating its accumulation under LDs. PRR‐mediated stabilization increases binding of CO to the promoter of FLOWERING LOCUS T ( FT ), leading to enhanced FT transcription and early flowering under these conditions. PRRs were previously reported to contribute to timekeeping by regulating CO transcription through their roles in the circadian clock. We propose an additional role for PRRs in which they act upon CO protein to promote flowering, directly coupling information on light exposure to the timekeeper and allowing recognition of LDs. Synopsis To promote flowering of Arabidopsis in response to day length, PSEUDO RESPONSE REGULATOR proteins interact with and stabilize the CONSTANS transcription factor at specific times of day. CONSTANS transcription factor is stabilized in the light by PSEUDO RESPONSE REGULATOR (PRR) proteins. In toc1 prr5 prr7 prr9 quadruple mutants, CO protein levels are reduced independently of the previously reported effects of prr mutations on CO transcription. Reduction of CO levels in toc1 prr5 prr7 prr9 plants requires the ubiquitin ligase COP1. PRR proteins interact directly with CO. In prr mutants, less CO protein is detected directly bound to its target gene FT. Graphical Abstract Transcription factor CONSTANS (CO) is a photoperiodic flowering timer in Arabidopsis . PRR circadian‐clock proteins bind and stabilize CO at specific times during the day to affect its accumulation and to thereby regulate seasonal flowering.