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Plant Cell Environ. 2016 Sep;39(9):1955-81. doi: 10.1111/pce.12754. Epub 2016 Jul 15.

Photoperiod-dependent changes in the phase of core clock transcripts and global transcriptional outputs at dawn and dusk in Arabidopsis.

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Max Planck Institute of Molecular Plant Physiology, Am Muehlenberg 1, 14476, Golm, Potsdam, Germany.
ARC Centre of Excellence for Translational Photosynthesis, Research School of Biology, Australian National University, GPO Box 475, Canberra, Australian Capital Territory, 2601, Australia.
Plant Systems Biology Lab, Plant and AgriBiosciences Research Centre, Botany and Plant Science, NUIG, Galway, Ireland.
SynthSys and School of Biological Sciences, C.H. Waddington Building, University of Edinburgh, Edinburgh, EH9 3BF, UK.


Plants use the circadian clock to sense photoperiod length. Seasonal responses like flowering are triggered at a critical photoperiod when a light-sensitive clock output coincides with light or darkness. However, many metabolic processes, like starch turnover, and growth respond progressively to photoperiod duration. We first tested the photoperiod response of 10 core clock genes and two output genes. qRT-PCR analyses of transcript abundance under 6, 8, 12 and 18 h photoperiods revealed 1-4 h earlier peak times under short photoperiods and detailed changes like rising PRR7 expression before dawn. Clock models recapitulated most of these changes. We explored the consequences for global gene expression by performing transcript profiling in 4, 6, 8, 12 and 18 h photoperiods. There were major changes in transcript abundance at dawn, which were as large as those between dawn and dusk in a given photoperiod. Contributing factors included altered timing of the clock relative to dawn, light signalling and changes in carbon availability at night as a result of clock-dependent regulation of starch degradation. Their interaction facilitates coordinated transcriptional regulation of key processes like starch turnover, anthocyanin, flavonoid and glucosinolate biosynthesis and protein synthesis and underpins the response of metabolism and growth to photoperiod.


circadian clock; metabolism

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