Plant and Cell Physiology Advance Access originally published online on July 30, 2005
Plant and Cell Physiology 2005 46(10):1591-1602; doi:10.1093/pcp/pci175
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Functional Characterization of Phytochrome Interacting Factor 3 for the Arabidopsis thaliana Circadian Clockwork
1 Plant Biology Institute, Biological Research Center, 62 Temesvari krt., Szeged, H-6726 Hungary
2 Biologie II/Institut für Botanik, University of Freiburg, 1 Schanzlestrasse Freiburg, D-79104 Germany
3 Department of Biological Sciences, University of Warwick, Gibbet Hill Road, Coventry, CV4 7AL UK
* Corresponding authors: Ferenc Nagy, E-mail, nagyf{at}nucleus.szbk.u-szeged.hu; Fax, +36-62-433-434; Laszlo Kozma-Bognar, E-mail, kozmab{at}nucleus.szbk.u-szeged.hu; Fax, +36-62-433-434.
Light, in a quality- and quantity-dependent fashion, induces nuclear import of the plant photoreceptors phytochromes and promotes interaction of these receptors with transcription factors including PHYTOCHROME INTERACTING FACTOR 3 (PIF3). PIF3 was shown to form in vitro a ternary complex with the G-box element of the promoters of LATE ELONGATED HYPOCOTYL (LHY) and CIRCADIAN CLOCK ASSOCIATED 1 (CCA1) and the Pfr conformer of phytochromes. CCA1 and LHY together with TIMING OF CAB EXPRESSION 1 (TOC1) constitute a transcriptional feed-back loop that is essential for a functional circadian clock in Arabidopsis. These findings led to the hypothesis that the PIF3-containing ternary complex regulates transcription of light-responsive genes and is involved in phototransduction to the central circadian clockwork. Here we report that (i) overexpression or lack of biologically functional PIF3 does not affect period length of rhythmic gene expression or red-light-induced resetting of the circadian clock and (ii) the transcription of PIF3 displays a low-amplitude circadian rhythm. We demonstrated previously that irradiation of etiolated seedlings induces rapid, phytochrome-controlled degradation of PIF3. Here we show that nuclear-localized PIF3 accumulates to relatively high levels by the end of the light phase in seedlings grown under diurnal conditions. Taken together, we show that (i) PIF3 does not play a significant role in controlling light input to and function of the circadian clockwork and (ii) a yet unknown mechanism limits phytochrome-induced degradation of PIF3 at the end of the day under diurnal conditions.
4 Present address: Institute of Molecular Plant Science, Kings Buildings, University of Edinburgh, Edinburgh EH9 3JH, United Kingdom.
(Received March 19, 2005; Accepted July 20, 2005)
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