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Molecular basis of seasonal time measurement in Arabidopsis


Several organisms have evolved the ability to measure daylength, or photoperiod, allowing them to adjust their development in anticipation of annual seasonal changes. Daylength measurement requires the integration of temporal information, provided by the circadian system, with light/dark discrimination, initiated by specific photoreceptors. Here we demonstrate that in Arabidopsis this integration takes place at the level of CONSTANS (CO)1 function. CO is a transcriptional activator that accelerates flowering time in long days, at least in part by inducing the expression of FLOWERING LOCUS T (FT)2,3,4,5. First, we show that precise clock control of the timing of CO expression, such that it is high during daytime only in long days, is critical for daylength discrimination. We then provide evidence that CO activation of FT expression requires the presence of light perceived through cryptochrome 2 (cry2) or phytochrome A (phyA). We conclude that an external coincidence mechanism, based on the endogenous circadian control of CO messenger RNA levels, and the modulation of CO function by light, constitutes the molecular basis for the regulation of flowering time by daylength in Arabidopsis.

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Figure 1: CO expression in the toc1-1 mutant and in wild-type plants.
Figure 2: FT expression in the toc1-1 mutant and in wild-type plants.
Figure 3: CO and FT expression in wild-type plants.
Figure 4: FT and CO expression in CO-overexpressing plants, and in wild-type, cry2 and phyA mutants.
Figure 5: Acute induction of FT expression by light.

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  1. Putterill, J., Robson, F., Lee, K., Simon, R. & Coupland, G. The CONSTANS gene of Arabidopsis promotes flowering and encodes a protein showing similarities to zinc finger transcription factors. Cell 80, 847–857 (1995)

    Article  CAS  Google Scholar 

  2. Samach, A. et al. Distinct role of CONSTANS target genes in reproductive development of Arabidopsis. Science 288, 1613–1616 (2000)

    Article  ADS  CAS  Google Scholar 

  3. Kardailsky, I. et al. Activation tagging of the floral inducer FT. Science 286, 1962–1965 (1999)

    Article  CAS  Google Scholar 

  4. Onouchi, H., Igeno, M. I., Perilleux, C., Graves, K. & Coupland, G. Mutagenesis of plants overexpressing CONSTANS demonstrates novel interactions among Arabidopsis flowering-time genes. Plant Cell 12, 885–900 (2000)

    Article  CAS  Google Scholar 

  5. Kobayashi, Y., Kaya, H., Goto, K., Iwabuchi, M. & Araki, T. A pair of related genes with antagonistic roles in mediating flowering signals. Science 286, 1960–1962 (1999)

    Article  CAS  Google Scholar 

  6. Samach, A. & Coupland, G. Time measurement and the control of flowering in plants. Bioessays 22, 38–47 (2000)

    Article  CAS  Google Scholar 

  7. Suarez-Lopez, P. et al. CONSTANS mediates between the circadian clock and the control of flowering in Arabidopsis. Nature 410, 1116–1120 (2001)

    Article  ADS  CAS  Google Scholar 

  8. Schaffer, R. et al. The late elongated hypocotyl mutation of Arabidopsis disrupts circadian rhythms and the photoperiodic control of flowering. Cell 93, 1219–1229 (1998)

    Article  CAS  Google Scholar 

  9. Hicks, K. A. et al. Conditional circadian dysfunction of the Arabidopsis early-flowering 3 mutant. Science 274, 790–792 (1996)

    Article  ADS  CAS  Google Scholar 

  10. Park, D. et al. Control of circadian rhythms and photoperiodic flowering by the Arabidopsis GIGANTEA gene. Science 285, 1579–1582 (1999)

    Article  CAS  Google Scholar 

  11. Zagotta, M. T. et al. The Arabidopsis ELF3 gene regulates vegetative photomorphogenesis and the photoperiodic induction of flowering. Plant J. 10, 691–702 (1996)

    Article  CAS  Google Scholar 

  12. Araki, T. & Komeda, Y. Analysis of the role of the late-flowering locus, GI, in the flowering of Arabidopsis thaliana. Plant J. 3, 231–239 (1993)

    Article  Google Scholar 

  13. Huq, E., Tepperman, J. M. & Quail, P. H. GIGANTEA is a nuclear protein involved in phytochrome signaling in Arabidopsis. Proc. Natl Acad. Sci. USA 97, 9789–9794 (2000)

    Article  ADS  CAS  Google Scholar 

  14. Strayer, C. et al. Cloning of the Arabidopsis clock gene TOC1, an autoregulatory response regulator homolog. Science 289, 768–771 (2000)

    Article  ADS  CAS  Google Scholar 

  15. Somers, D. E., Webb, A. A. R., Pearson, M. & Kay, S. The short-period mutant, toc1-1, alters circadian clock regulation of multiple outputs throughout development in Arabidopsis thaliana. Development 125, 485–494 (1998)

    CAS  PubMed  Google Scholar 

  16. Millar, A. J., Carré, I. A., Strayer, C. A., Chua, N.-H. & Kay, S. A. Circadian clock mutants in Arabidopsis identified by luciferase imaging. Science 267, 1161–1163 (1995)

    Article  ADS  CAS  Google Scholar 

  17. Alabadi, D. et al. Reciprocal regulation between TOC1 and LHY/CCA1 within the Arabidopsis circadian clock. Science 293, 880–883 (2001)

    Article  CAS  Google Scholar 

  18. Guo, H. W., Yang, W. Y., Mockler, T. C. & Lin, C. T. Regulation of flowering time by Arabidopsis photoreceptors. Science 279, 1360–1363 (1998)

    Article  ADS  CAS  Google Scholar 

  19. Johnson, E., Bradley, M., Harberd, N. P. & Whitelam, G. C. Photoresponses of light-grown phyA mutants of Arabidopsis. Phytochrome A is required for the perception of daylength extensions. Plant Physiol. 105, 141–149 (1994)

    Article  CAS  Google Scholar 

  20. Corbesier, L., Gadisseur, I., Silvestre, G., Jacqmard, A. & Bernier, G. Design in Arabidopsis of a synchronous system of floral induction by one long day. Plant J. 9, 947–952 (1996)

    Article  CAS  Google Scholar 

  21. Bünning, E. Die endogene Tagesrhthmik als Grundlage der photoperiodischen Reaktion. Ber. Dtsch Bot. Ges. 54, 590–607 (1936)

    Google Scholar 

  22. Pittendrigh, C. S. & Minis, D. H. The entrainment of circadian oscillations by light and their role as photoperiodic clocks. Am. Nat. 98, 261–294 (1964)

    Article  Google Scholar 

  23. Pittendrigh, C. S. Circadian rhythms and the circadian organization of living systems. Cold Spring Harbor Symp. Quant. Biol. 25, 159–184 (1960)

    Article  CAS  Google Scholar 

  24. Yanovsky, M. J. & Kay, S. A. Signaling networks in the plant circadian system. Curr. Opin. Plant Biol. 4, 429–435 (2001)

    Article  CAS  Google Scholar 

  25. Blazquez, M. A. & Weigel, D. Independent regulation of flowering by phytochrome B and gibberellins in Arabidopsis. Plant Physiol. 120, 1025–1032 (1999)

    Article  CAS  Google Scholar 

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We thank J. J. Casal, S. Harmer, P. Mas and F. Harmon for critical reading of the manuscript. This work was supported by an NIH grant to S.A.K. The work of M.J.Y. was initially supported by Conicet, Antorchas and the University of Buenos Aires and, more recently, by the Pew Foundation.

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Correspondence to Steve A. Kay.

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Yanovsky, M., Kay, S. Molecular basis of seasonal time measurement in Arabidopsis. Nature 419, 308–312 (2002).

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