The Arabidopsis pseudo-response regulators, PRR5 and PRR7, coordinately play essential roles for circadian clock function.

In Arabidopsis thaliana, a number of clock-associated protein factors have been identified. Among them, TOC1 (TIMING OF CAB EXPRESSION 1) is believed to be a component of the central oscillator. TOC1 is a member of a small family of proteins, designated as ARABIDOPSIS PSEUDO-RESPONSE REGULATOR, including PRR1/TOC1, PRR3, PRR5, PRR7 and PRR9. It has not been certain whether or not other PRR family members are also implicated in clock function per se. To clarify this problem, here we constructed a double mutant line, which is assumed to have severe lesions in both the PRR5 and PRR7 genes. Resulting homozygous prr5-11 prr7-11 young seedlings showed a marked phenotype of hyposensitivity to red light during de-etiolation. In addition, they displayed a phenotype of extremely late flowering under long-day photoperiod conditions, but not short-day conditions. The rhythms at the level of transcription of certain clock-controlled genes were severely perturbed in the double mutant plants when they were released into continuous light (LL) and darkness (DD). The observed phenotype was best interpreted as 'arrhythmic in both LL and DD' and/or 'very short period with markedly reduced amplitude'. Even under the light entrainment (LD) conditions, the mutant plants showed anomalous diurnal oscillation profiles with altered amplitude and/or phase with regard to certain clock-controlled genes, including the clock component CCA1 (CIRCADIAN CLOCK-ASSOCIATED 1) gene. Such events were observed even under temperature entrainment conditions, suggesting that the prr5-11 prr7-11 lesions cannot simply be attributed to a defect in the light signal input pathway. These pleiotropic circadian-associated phenotypes of the double mutant were very remarkable, as compared with those observed previously for each single mutant. Taking these results together, we propose for the first time that PRR5 and PRR7 coordinately (or synergistically) play essential clock-associated roles close to the central oscillator.

[1]  Tsuyoshi Mizoguchi,et al.  LHY and CCA1 are partially redundant genes required to maintain circadian rhythms in Arabidopsis. , 2002, Developmental cell.

[2]  K. Shinozaki,et al.  Identification of ASK and clock-associated proteins as molecular partners of LKP2 (LOV kelch protein 2) in Arabidopsis. , 2004, Journal of experimental botany.

[3]  Martin Straume,et al.  Least-Squares Analysis of Fluorescence Data , 2002 .

[4]  E. M. Meyerowitz,et al.  Arabidopsis thaliana , 2022, CABI Compendium.

[5]  P. Quail,et al.  Signalling in light-controlled development. , 1999, Seminars in cell & developmental biology.

[6]  J. Lakowicz.  Topics in fluorescence spectroscopy , 2002 .

[7]  S. Tabata,et al.  A Link between circadian-controlled bHLH factors and the APRR1/TOC1 quintet in Arabidopsis thaliana. , 2003, Plant & cell physiology.

[8]  Claire Périlleux,et al.  Mutagenesis of Plants Overexpressing CONSTANS Demonstrates Novel Interactions among Arabidopsis Flowering-Time Genes , 2000, Plant Cell.

[9]  Takeshi Mizuno,et al.  The APRR3 component of the clock-associated APRR1/TOC1 quintet is phosphorylated by a novel protein kinase belonging to the WNK family, the gene for which is also transcribed rhythmically in Arabidopsis thaliana. , 2002, Plant & cell physiology.

[10]  P. Quail,et al.  Arabidopsis PSEUDO-RESPONSE REGULATOR7 Is a Signaling Intermediate in Phytochrome-Regulated Seedling Deetiolation and Phasing of the Circadian Clock Article, publication date, and citation information can be found at www.plantcell.org/cgi/doi/10.1105/tpc.015065. , 2003, The Plant Cell Online.

[11]  D. E. Somers,et al.  Phytochromes and cryptochromes in the entrainment of the Arabidopsis circadian clock. , 1998, Science.

[12]  S. Kay,et al.  A Role for LKP2 in the Circadian Clock of Arabidopsis Article, publication date, and citation information can be found at www.plantcell.org/cgi/doi/10.1105/tpc.010332. , 2001, The Plant Cell Online.

[13]  J. Ecker,et al.  An Arabidopsis circadian clock component interacts with both CRY1 and phyB , 2001, Nature.

[14]  S. Kay,et al.  Molecular basis of seasonal time measurement in Arabidopsis , 2002, Nature.

[15]  Louis J. Brown,et al.  Characterization of CIREN , 2001 .

[16]  T. Mizuno,et al.  Circadian waves of expression of the APRR1/TOC1 family of pseudo-response regulators in Arabidopsis thaliana: insight into the plant circadian clock. , 2000, Plant & cell physiology.

[17]  S. Tabata,et al.  Comparative genetic studies on the APRR5 and APRR7 genes belonging to the APRR1/TOC1 quintet implicated in circadian rhythm, control of flowering time, and early photomorphogenesis. , 2003, Plant & cell physiology.

[18]  T. Mizuno,et al.  Aberrant expression of the Arabidopsis circadian-regulated APRR5 gene belonging to the APRR1/TOC1 quintet results in early flowering and hypersensitiveness to light in early photomorphogenesis. , 2002, Plant & cell physiology.

[19]  A. Peeters,et al.  GENETIC CONTROL OF FLOWERING TIME IN ARABIDOPSIS. , 1998, Annual review of plant physiology and plant molecular biology.

[20]  Andrew J Millar,et al.  The Circadian Clock. A Plant's Best Friend in a Spinning World1 , 2003, Plant Physiology.

[21]  E. Tobin,et al.  The protein kinase CK2 is involved in regulation of circadian rhythms in Arabidopsis. , 1999, Proceedings of the National Academy of Sciences of the United States of America.

[22]  T. Mizuno,et al.  Circadian-controlled basic/helix-loop-helix factor, PIL6, implicated in light-signal transduction in Arabidopsis thaliana. , 2004, Plant & cell physiology.

[23]  T. Mizuno,et al.  Characterization of plant circadian rhythms by employing Arabidopsis cultured cells with bioluminescence reporters. , 2004, Plant & cell physiology.

[24]  S. Kay,et al.  Time zones: a comparative genetics of circadian clocks , 2001, Nature Reviews Genetics.

[25]  T. Mizuno,et al.  His-Asp phosphotransfer signal transduction. , 1998, Journal of biochemistry.

[26]  D. E. Somers,et al.  Targeted degradation of TOC1 by ZTL modulates circadian function in Arabidopsis thaliana , 2003, Nature.

[27]  Michael F. Covington,et al.  ELF3 Modulates Resetting of the Circadian Clock in Arabidopsis , 2001, The Plant Cell Online.

[28]  D. E. Somers,et al.  Cloning of the Arabidopsis clock gene TOC1, an autoregulatory response regulator homolog. , 2000, Science.

[29]  D. E. Somers.  Clock-associated genes in Arabidopsis: a family affair. , 2001, Philosophical transactions of the Royal Society of London. Series B, Biological sciences.

[30]  S. Tabata,et al.  Characterization of the APRR9 pseudo-response regulator belonging to the APRR1/TOC1 quintet in Arabidopsis thaliana. , 2003, Plant & cell physiology.

[31]  T. Mizuno,et al.  Cell autonomous circadian waves of the APRR1/TOC1 quintet in an established cell line of Arabidopsis thaliana. , 2003, Plant & cell physiology.

[32]  Andrew J. Millar,et al.  The ELF4 gene controls circadian rhythms and flowering time in Arabidopsis thaliana , 2002, Nature.

[33]  P. Quail,et al.  Phytochrome photosensory signalling networks , 2002, Nature Reviews Molecular Cell Biology.

[34]  T. Mizuno,et al.  The APRR 1 / TOC 1 Quintet Implicated in Circadian Rhythms of Arabidopsis thaliana : II . Characterization with CCA 1-Overexpressing Plants , 2001 .

[35]  S. Kay,et al.  Living by the calendar: how plants know when to flower , 2003, Nature Reviews Molecular Cell Biology.

[36]  Joanna Putterill,et al.  The late elongated hypocotyl Mutation of Arabidopsis Disrupts Circadian Rhythms and the Photoperiodic Control of Flowering , 1998, Cell.

[37]  Zhi-Yong Wang,et al.  Constitutive Expression of the CIRCADIAN CLOCK ASSOCIATED 1 (CCA1) Gene Disrupts Circadian Rhythms and Suppresses Its Own Expression , 1998, Cell.

[38]  T. Mizuno,et al.  Aberrant expression of the light-inducible and circadian-regulated APRR9 gene belonging to the circadian-associated APRR1/TOC1 quintet results in the phenotype of early flowering in Arabidopsis thaliana. , 2002, Plant & cell physiology.

[39]  G. Coupland,et al.  GIGANTEA: a circadian clock‐controlled gene that regulates photoperiodic flowering in Arabidopsis and encodes a protein with several possible membrane‐spanning domains , 1999, The EMBO journal.

[40]  E. Huq,et al.  GIGANTEA is a nuclear protein involved in phytochrome signaling in Arabidopsis. , 2000, Proceedings of the National Academy of Sciences of the United States of America.

[41]  Takeshi Mizuno,et al.  The APRR1/TOC1 quintet implicated in circadian rhythms of Arabidopsis thaliana: I. Characterization with APRR1-overexpressing plants. , 2002, Plant & cell physiology.

[42]  D. E. Somers,et al.  ZEITLUPE Encodes a Novel Clock-Associated PAS Protein from Arabidopsis , 2000, Cell.

[43]  David Alabadí,et al.  Dual Role of TOC1 in the Control of Circadian and Photomorphogenic Responses in Arabidopsis Online version contains Web-only data. Article, publication date, and citation information can be found at www.plantcell.org/cgi/doi/10.1105/tpc.006734. , 2003, The Plant Cell Online.

[44]  D. R. Wagner,et al.  EARLY FLOWERING3 Encodes a Novel Protein That Regulates Circadian Clock Function and Flowering in Arabidopsis , 2001, The Plant Cell Online.

[45]  A. Hall,et al.  Response regulator homologues have complementary, light-dependent functions in the Arabidopsis circadian clock , 2003, Planta.

[46]  S. Kay,et al.  tej defines a role for poly(ADP-ribosyl)ation in establishing period length of the arabidopsis circadian oscillator. , 2002, Developmental cell.

[47]  Isabelle A. Carr.  Day-Length Perception and the Photoperiodic Regulation of Flowering in Arabidopsis , 2001 .

[48]  A. Millar,et al.  Circadian dysfunction causes aberrant hypocotyl elongation patterns in Arabidopsis. , 1999, The Plant journal : for cell and molecular biology.

[49]  C. R. McClung,et al.  Enhanced Fitness Conferred by Naturally Occurring Variation in the Circadian Clock , 2003, Science.

[50]  D. E. Somers,et al.  The F-Box Protein ZEITLUPE Confers Dosage-Dependent Control on the Circadian Clock, Photomorphogenesis, and Flowering Time Online version contains Web-only data. , 2004, The Plant Cell Online.

[51]  J. Chory,et al.  The Arabidopsis SRR1 gene mediates phyB signaling and is required for normal circadian clock function. , 2003, Genes & development.

[52]  C. R. McClung.  Circadian rhythms in plants: a millennial view , 2000 .

[53]  Stacey L. Harmer,et al.  Critical Role for CCA1 and LHY in Maintaining Circadian Rhythmicity in Arabidopsis , 2002, Current Biology.

[54]  E. Tobin,et al.  Loss of the circadian clock-associated protein 1 in Arabidopsis results in altered clock-regulated gene expression. , 1999, Proceedings of the National Academy of Sciences of the United States of America.

[55]  T. Mizuno,et al.  The evolutionarily conserved OsPRR quintet: rice pseudo-response regulators implicated in circadian rhythm. , 2003, Plant & cell physiology.

[56]  T. Mizuno,et al.  Characterization of circadian-associated APRR3 pseudo-response regulator belonging to the APRR1/TOC1 quintet in Arabidopsis thaliana. , 2004, Plant & cell physiology.

[57]  G. Coupland,et al.  Control of flowering time: interacting pathways as a basis for diversity. , 2002, The Plant cell.

[58]  T. Mizuno,et al.  Genes encoding pseudo-response regulators: insight into His-to-Asp phosphorelay and circadian rhythm in Arabidopsis thaliana. , 2000, Plant & cell physiology.

[59]  T. Mizuno,et al.  Expression of Arabidopsis response regulator homologs is induced by cytokinins and nitrate , 1998, FEBS letters.

[60]  D. E. Somers,et al.  The short-period mutant, toc1-1, alters circadian clock regulation of multiple outputs throughout development in Arabidopsis thaliana. , 1998, Development.

[61]  Steve A. Kay,et al.  Reciprocal Regulation Between TOC1 and LHY/CCA1 Within the Arabidopsis Circadian Clock , 2001, Science.

[62]  T. Mizuno,et al.  Light response of the circadian waves of the APRR1/TOC1 quintet: when does the quintet start singing rhythmically in Arabidopsis? , 2001, Plant & cell physiology.

[63]  C. Bishop.  Control of Flowering , 2003, Genome Biology.

[64]  B. Bartel,et al.  FKF1, a Clock-Controlled Gene that Regulates the Transition to Flowering in Arabidopsis , 2000, Cell.

[65]  T. Mizuno.  Plant response regulators implicated in signal transduction and circadian rhythm. , 2004, Current opinion in plant biology.