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Science 339 (6125): 1316-1319

Copyright © 2013 by the American Association for the Advancement of Science

Circadian Control of Chloroplast Transcription by a Nuclear-Encoded Timing Signal

Zeenat B. Noordally1, Kenyu Ishii2, Kelly A. Atkins3, Sarah J. Wetherill3, Jelena Kusakina4, Eleanor J. Walton3, Maiko Kato2, Miyuki Azuma5, Kan Tanaka6, Mitsumasa Hanaoka2, and Antony N. Dodd4,*

1 SynthSys, University of Edinburgh, C H Waddington Building, Mayfield Road, Edinburgh EH9 3JD, UK.
2 Graduate School of Horticulture, Chiba University, 648 Matsudo, Matsudo, Chiba 271-8510, Japan.
3 Department of Biology, University of York, York YO10 5DD, UK.
4 School of Biological Sciences, University of Bristol, Bristol BS8 1UG, UK.
5 Institute of Molecular and Cellular Biosciences, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-0032, Japan.
6 Chemical Resources Laboratory, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama 226-8503, Japan.

Figure 1
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Fig. 1. Nuclear-encoded SIG5 is required for circadian oscillations of the chloroplast gene psbD. (A) Circadian regulation of mRNA encoding two sigma factors and psbD BLRP. (B) Time of circadian peak of DF in wild type, sig5-2, and sig5-3, ± SEM. Of three experiments, experiment 3 was experimenter-blind throughout experimentation and analysis. (C and D) Under constant light (C) and light-dark cycles (D), relative abundance of SIG5, psbD BLRP, and psbDC total transcripts in wild type and sig5 mutants. psbD BLRP indicates the abundance of mRNAs transcribed from the SIG5-dependent BLRP promoter of psbD; psbDC total transcripts are transcripts produced by the combined action of all transcription start sites of the psbDC operon. Hatched bars beside x axes indicate subjective darkness; solid bars indicate actual darkness. In two-sample t tests comparing times of circadian peaks of DF, significance of results: *P < 0.05, **P < 0.01; the peak time difference between Col-0 and sig5-2 for repeat 2 is less significant (P = 0.063).


Figure 2
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Fig. 2. The circadian timing of SIG5 transcription by the eukaryotic circadian oscillator controls circadian rhythms of transcription of the chloroplast psbD BLRP. (A) The circadian phase of SIG5 transcripts was advanced relative to the wild type by expressing SIG5 under the control of the TOC1 promoter in the sig5-3 background (TOC1::SIG5 line 1, top), and the circadian timing of SIG5 can control the timing of psbD BLRP transcripts (bottom). (B) Short- and long-period circadian clock mutants cause short and long circadian periods of SIG5 and psbD BLRP transcripts. Period estimated from cosinor analysis is plotted against pMMC-β measure of rhythmic robustness.


Figure 3
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Fig. 3. SIG5-mediated signaling to the chloroplast forms an output pathway from the eukaryotic circadian oscillator. (A) In wild type and the sig5-3 mutant, abundance of transcripts encoding core oscillator components in seedlings entrained previously to light-dark cycles. (B and C) Circadian oscillations of CCA1, TOC1, and CCR2 promoter activity in wild type and sig5-3 measured by bioluminescence imaging of promoter-luciferase fusion reporters. (B) Integrated luciferase bioluminescence counts measured at 2-hour intervals under constant light; (C) comparison of period and relative amplitude error (RAE) for promoter-luciferase reporters.


Figure 4
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Fig. 4. Circadian gating of blue light induction of SIG5 and psbD BLRP. The magnitude of SIG5 transcript induction by blue light has a circadian oscillation (top), and the magnitude of psbD BLRP induction by blue light is circadian regulated and SIG5-dependent (bottom). SIG5 and psbD BLRP transcripts were measured 1 hour and 2 hours after induction with 50 μmol m–2 s–1 blue light, respectively. Seedlings were entrained previously to light/dark cycles, then transferred to 5 μmol m–2 s–1 red light to maintain oscillator rhythmicity during the experiment. Hatched bars above x axes indicate subjective dark period.


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