Editors' ChoicePlant biology

Slave to the Rhythm

Sci. Signal.  23 Dec 2008:
Vol. 1, Issue 51, pp. ec442
DOI: 10.1126/scisignal.151ec442

Most organisms, from bacteria to humans, harbor endogenous clocks that cycle with a period of about 24 hours. These clocks function within individual cells and comprise regulatory feedback loops of transcriptional and posttranslational processes. Plants are thought to use a circadian clock consisting of three light-sensitive, interlocked transcription-translation feedback loops. Because experiments have generally used plants grown on agar plates—where the roots are exposed to light—the fact that a different circadian clock operates in plant roots has been obscured. By growing plants hydroponically with the roots in darkness, James et al. discovered that the root circadian clock is a stripped-down version of the clock that operates in the shoots, operating on only one of the feedback loops and regulating only a small number of genes. In roots, two of the feedback loops are inactivated, in that two clock components (CCA1 and LHY) do not regulate gene expression as they do in shoots. However, the shoot and root clocks are synchronized under normal day/night conditions, possibly by circulating metabolic signals, making the root clock essentially a “slave” to the shoot clock.

A. B. James, J. A. Monreal, G. A. Nimmo, C. L. Kelly, P. Herzyk, G. I. Jenkins, H. G. Nimmo, The circadian clock in Arabidopsis roots is a simplified slave version of the clock in shoots. Science 322, 1832–1835 (2008). [Abstract] [Full Text]