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Science 336 (6077): 75-79

Copyright © 2012 by the American Association for the Advancement of Science

Mapping the Core of the Arabidopsis Circadian Clock Defines the Network Structure of the Oscillator

W. Huang,1 P. Pérez-García,1 A. Pokhilko,2 A. J. Millar,2,3 I. Antoshechkin,4 J. L. Riechmann,1,4,5 P. Mas1,*

Abstract: In many organisms, the circadian clock is composed of functionally coupled morning and evening oscillators. In Arabidopsis, oscillator coupling relies on a core loop in which the evening oscillator component TIMING OF CAB EXPRESSION 1 (TOC1) was proposed to activate a subset of morning-expressed oscillator genes. Here, we show that TOC1 does not function as an activator but rather as a general repressor of oscillator gene expression. Repression occurs through TOC1 rhythmic association to the promoters of the oscillator genes. Hormone-dependent induction of TOC1 and analysis of RNA interference plants show that TOC1 prevents the activation of morning-expressed genes at night. Our study overturns the prevailing model of the Arabidopsis circadian clock, showing that the morning and evening oscillator loops are connected through the repressing activity of TOC1.

1 Center for Research in Agricultural Genomics, Barcelona 08193, Spain.
2 School of Biological Sciences, University of Edinburgh, Edinburgh EH9 3JH, UK.
3 Centre for Systems Biology at Edinburgh, C. H. Edinburgh EH9 3JD, UK.
4 California Institute of Technology, Division of Biology, Pasadena, CA 91125, USA.
5 Institució Catalana de Recerca i Estudis Avançats, Barcelona 08010, Spain.

* To whom correspondence should be addressed. E-mail: paloma.mas{at}

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