Plant and Cell Physiology Advance Access originally published online on May 15, 2007
Plant and Cell Physiology 2007 48(6):822-832; doi:10.1093/pcp/pcm056
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Arabidopsis Clock-Associated Pseudo-Response Regulators PRR9, PRR7 and PRR5 Coordinately and Positively Regulate Flowering Time Through the Canonical CONSTANS-Dependent Photoperiodic Pathway
1Division of Biological Science, Graduate School of Science, Nagoya University, Chikusa-ku, Nagoya, 464-8602 Japan
2Laboratory of Molecular Microbiology, School of Agriculture, Nagoya University, Chikusa-ku, Nagoya, 464-8601 Japan
3Institute of Biological Sciences, University of Tsukuba, Tsukuba, Ibaraki, 305-8572 Japan
*Corresponding author: Email, nnakamichi{at}bio.nagoya-u.ac.jp; Fax, +81-52-789-4091.
| Abstract |
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Photoperiodism allows organisms to measure daylength, or external photoperiod, and to anticipate coming seasons. Daylength measurement requires the integration of light signal and temporal information by the circadian clock. In the long-day plant Arabidopsis thaliana, CONSTANS (CO) plays a crucial role in integrating the circadian rhythm and environmental light signals into the photoperiodic flowering pathway. Nevertheless, the molecular mechanism by which the circadian clock modulates the cyclic expression profile of CO is poorly understood. Here, we first showed that the clock-associated genes PSEUDO-RESPONSE REGULATOR (PRR) PRR9, PRR7 and PRR5 are involved in activation of CO expression during the daytime. Then, extensive genetic studies using CIRCADIAN CLOCK-ASSOCIATED1 (CCA1)/LATE ELONGATED HYPOCOTYL (LHY) double mutants (cca1/lhy) and prr7/prr5 were conducted. The results suggested that PRR genes act coordinately in a manner parallel with and antagonistic to CCA/LHY, upstream of the canonical COFLOWERING LOCUS T (FT) photoperiodic flowering pathway. Finally, we provided evidence to propose a model, in which CCA1/LHY repress CO through GIGANTEA (GI), while PRR9, PRR7 and PRR5 activate CO predominantly by repressing CYCLING DOF FACTOR1 (CDF1) encoding a DNA-binding transcriptional repressor.
Keywords: Arabidopsis thaliana - Circadian rhythm - COFT - Photoperiodic flowering - PRR
Abbreviations: CCA1, CIRCADIAN CLOCK-ASSOCIATED 1; CDF1, CYCLING DOF FACTOR 1; CO, CONSTANS; FT, FLOWERING LOCUS T; GI, GIGANTEA; LD, long-day conditions; LHY, LATE ELONGATED HYPOCOTYL; PRR, PSEUDO-RESPONSE REGULATOR; QTL, quantitative trait locus; SD, short-day conditions; TOC1, TIMING OF CAB EXPRESSION 1; ZT, Zeitgeber time.
(Received February 19, 2007; Accepted May 6, 2007)
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