Response regulator homologues have complementary, light-dependent functions in the Arabidopsis circadian clock.
ABSTRACT 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.
- SourceAvailable from: Steve A Kay[Show abstract] [Hide abstract]
ABSTRACT: The circadian clock perceives environmental signals to reset to local time, but the underlying molecular mechanisms are not well understood. Here we present data revealing that a member of the heat shock factor (Hsf) family is involved in the input pathway to the plant circadian clock. Using the yeast one-hybrid approach, we isolated several Hsfs, including HEAT SHOCK FACTOR B2b (HsfB2b), a transcriptional repressor that binds the promoter of PSEUDO RESPONSE REGULATOR 7 (PRR7) at a conserved binding site. The constitutive expression of HsfB2b leads to severely reduced levels of the PRR7 transcript and late flowering and elongated hypocotyls. HsfB2b function is important during heat and salt stress because HsfB2b overexpression sustains circadian rhythms, and the hsfB2b mutant has a short circadian period under these conditions. HsfB2b is also involved in the regulation of hypocotyl growth under warm, short days. Our findings highlight the role of the circadian clock as an integrator of ambient abiotic stress signals important for the growth and fitness of plants.Proceedings of the National Academy of Sciences of the United States of America. 10/2014;
- [Show abstract] [Hide abstract]
ABSTRACT: An interlocking multi-loop model has been generally accepted to describe the transcriptional circuitry of core clock genes, through which robust circadian rhythms are generated in Arabidopsis thaliana. The circadian clock must have the ability to integrate ambient temperature signals into the clock transcriptional circuitry to properly regulate clock function. Clarification of the underlying mechanism is a longstanding subject in the field. Here, we provide evidence that temperature signals feed into the clock transcriptional circuitry through the evening complex (EC) nighttime repressor consisting of ELF3, ELF4, and LUX (also known as PCL1). Chromatin immunoprecipitation assays showed that PRR7, GI and LUX are direct targets of the nighttime repressor. Consequently, transcription of PRR9/PRR7, GI and LUX is commonly regulated through the nighttime repressor in response to both moderate changes in temperature (Δ6°C) and differences in steady-state growth-compatible temperature (16°C to 28°C). A warmer temperature inhibits EC function more, whereas a cooler temperature stimulates it more. Consequently, the expression of these target genes is upregulated in response to a warm temperature specifically during the dark period, whereas they are reversibly downregulated in response to a cool temperature. Transcription of another EC-target, the PIF4 gene, is modulated through the same thermoregulatory mechanism. The last finding revealed the sophisticated physiological mechanism underlying the clock-controlled output pathway, which leads to the PIF4-mediated temperature-adaptive regulation of hypocotyl elongation.Plant and Cell Physiology 02/2014; · 4.98 Impact Factor
- [Show abstract] [Hide abstract]
ABSTRACT: Although rhythmic leaf movement in a higher plant was the first physiological process recognised to be under circadian control, our understanding of the molecular drives underlying circadian rhythms in plants is still limited. Genetic screens for mutants impaired with regard to circadian rhythmicity have identified components critical for clock function in the model plant Arabidopsis thaliana, providing a snapshot of interconnected transcription-based feedback circuits at the core of the clockwork. Subsequently, the Arabidopsis genome project provided the basis for reverse genetic approaches to uncover additional gene products operating close to the core clockwork. We will review recent progress in the dissection of the molecular mechanisms within the basic oscillator and in the incorporation of additional components into the basic clock model.Biological Rhythm Research 01/2006; 37(4):335-352. · 1.22 Impact Factor