Response regulator homologs have complementary, light-dependent functions in the Arabidopsis circadian clock

Department of Biological Sciences, University of Warwick, Coventry, CV4 7AL, UK.
Planta (Impact Factor: 3.26). 12/2003; 218(1):159-62. DOI: 10.1007/s00425-003-1106-4
Source: PubMed


TIMING OF CAB EXPRESSION 1 ( TOC1) functions with CIRCADIAN CLOCK-ASSOCIATED 1 (CCA1) in a transcriptional feedback loop that is important for the circadian clock in Arabidopsis thaliana (L.) Heynh. TOC1 and its four paralogues, the Arabidopsis PSEUDO-RESPONSE REGULATOR (PRR) genes, are expressed in an intriguing daily sequence. This was proposed to form a second feedback loop, similar to the interlocking clock gene circuits in other taxa. We show that prr9 and prr5 null mutants have reciprocal period defects for multiple circadian rhythms, consistent with subtly altered expression patterns of CCA1 and TOC1. The period defects are conditional on light quality and combine additively in double-mutant plants. Thus PRR9 and PRR5 modulate light input to the circadian clock but are neither uniquely required for rhythm generation nor form a linear series of mutual PRR gene regulation.

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Available from: Maria Elenor Eriksson, Aug 21, 2015
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    • "TOC1 protein is expressed in the evening and, in turn, activates CCA1 expression , partly by antagonizing a transcriptional repressor of CCA1, CCA1 HIKING EXPEDITION (CHE) of the TCP (for TEOSINTE BRANCHED1, CYCLOIDEA, and PCF) family (Pruneda-Paz et al., 2009). In addition to TOC1, numerous genetic studies have demonstrated the importance of other PRR genes in the circadian clock (Eriksson et al., 2003; Kaczorowski and Quail, 2003; Michael et al., 2003; Yamamoto et al., 2003; Farre et al., 2005; Nakamichi et al., 2005; Salome and McClung, 2005; Para et al., 2007; Ito et al., 2009). "
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    ABSTRACT: An interlocking transcriptional-translational feedback loop of clock-associated genes is thought to be the central oscillator of the circadian clock in plants. TIMING OF CAB EXPRESSION1 (also called PSEUDO-RESPONSE REGULATOR1 [PRR1]) and two MYB transcription factors, CIRCADIAN CLOCK ASSOCIATED1 (CCA1) and LATE ELONGATED HYPOCOTYL (LHY), play pivotal roles in the loop. Genetic studies have suggested that PRR9, PRR7, and PRR5 also act within or close to the loop; however, their molecular functions remain unknown. Here, we demonstrate that PRR9, PRR7, and PRR5 act as transcriptional repressors of CCA1 and LHY. PRR9, PRR7, and PRR5 each suppress CCA1 and LHY promoter activities and confer transcriptional repressor activity to a heterologous DNA binding protein in a transient reporter assay. Using a glucocorticoid-induced PRR5-GR (glucorticoid receptor) construct, we found that PRR5 directly downregulates CCA1 and LHY expression. Furthermore, PRR9, PRR7, and PRR5 associate with the CCA1 and LHY promoters in vivo, coincident with the timing of decreased CCA1 and LHY expression. These results suggest that the repressor activities of PRR9, PRR7, and PRR5 on the CCA1 and LHY promoter regions constitute the molecular mechanism that accounts for the role of these proteins in the feedback loop of the circadian clock.
    Full-text · Article · Mar 2010 · The Plant Cell
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    • "For instance, the expression levels of many clock genes (including CCA1, LHY, PRR7, PRR9, and GIGANTEA; GI) are upregulated by light (Wang and Tobin 1998; Martinez-Garcia et al. 2000; Eriksson et al. 2003; Farre et al. 2005; Locke et al. 2005; Farre and Kay 2007). Indeed, mutations in PRR7 and PRR9 only cause a long period in constantly lit conditions (Eriksson et al. 2003; Farre et al. 2005) suggesting that these genes act in pathways to modulate the effect of light on the entrainment of the circadian clock. Although little is known regarding the biochemical function of TOC1, recent years have seen steady gains in our knowledge of light-mediated protein stability of this protein. "
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    ABSTRACT: The rising and setting of the sun marks a transition between starkly contrasting environmental conditions for vegetative life. Given these differing diurnal and nocturnal environmental factors and the inherent regularity of the transition between the two, it is perhaps unsurprising that plants have developed an internal timing mechanism (known as a circadian clock) to allow modulation of gene expression and metabolism in response to external cues. Entrainment of the circadian clock, primarily via the detection of changes in light and temperature, maintains synchronization between the surrounding environment and the endogenous clock mechanism. In this review, recent advances in our understanding of the molecular workings of the plant circadian clock are discussed as are the input pathways necessary for entrainment of the clock machinery.
    Preview · Article · Jun 2009 · Journal of Plant Biology
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    • "However, current evidence indicates that the Arabidopsis oscillator comprises several interlocking feedback loops, comparable to those identified in the circadian systems of other eukaryotes [7]–[9]. Besides having established roles for the primary clock genes LHY, CCA1 and TOC1 in the oscillator feedback network, experimental data point to the participation in this mechanism of several PSEUDO-RESPONSE REGULATOR (PRR) genes, belonging to the same family as TOC1/PRR1 [10]–[14]. This family consists of five members that are expressed after dawn in the sequential order PRR9→PRR7→PRR5→PRR3→TOC1 [15]. "
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    ABSTRACT: Cold acclimation in woody plants may have special features compared to similar processes in herbaceous plants. Recent studies have shown that circadian clock behavior in the chestnut tree (Castanea sativa) is disrupted by cold temperatures and that the primary oscillator feedback loop is not functional at 4 degrees C or in winter. In these conditions, CsTOC1 and CsLHY genes are constantly expressed. Here, we show that this alteration also affects CsPRR5, CsPRR7 and CsPRR9. These genes are homologous to the corresponding Arabidopsis PSEUDO-RESPONSE REGULATOR genes, which are also components of the circadian oscillator feedback network. The practically constant presence of mRNAs of the 5 chestnut genes at low temperature reveals an unknown aspect of clock regulation and suggests a mechanism regulating the transcription of oscillator genes as a whole.
    Full-text · Article · Feb 2008 · PLoS ONE
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