Plant Physiology Preview
Published on January 20, 2006; 10.1104/pp.105.074864
Received November 29, 2005
Returned for revision December 21, 2005
Accepted December 21, 2005
Forward genetic analysis of the circadian clock separates the multiple functions of ZEITLUPE
Éva Kevei , Péter Gyula , Anthony Hall , László Kozma-Bognár , Woe-Yeon Kim , Maria E. Eriksson , Réka Tóth , Shigeru Hanano , Balázs Fehér , Megan M. Southern , Ruth M. Bastow , András Viczián , Victoria Hibberd , Seth J. Davis , David E. Somers , Ferenc Nagy , and Andrew J. Millar *
Institute of Plant Biology, Biological Research Centre of the Hungarian Academy of Sciences, Szeged, Hungary
School of Biological Sciences, University of Liverpool, Liverpool, United Kingdom
Institute of Molecular Plant Science, Kings Buildings, University of Edinburgh, Edinburgh, United Kingdom
Department of Plant Cellular and Molecular Biology, Ohio State University, Columbus, USA
Department of Plant Physiology, Umeå University, Umeå, Sweden
Department of Plant Developmental Biology, Max Planck Institute for Plant Breeding Research, Cologne, Germany
Department of Biological Sciences, University of Warwick, Coventry, United Kingdom
Biologie II/Institut für Botanik, University of Freiburg, Freiburg, Germany
* Corresponding author; email: andrew.millar{at}ed.ac.uk.
The circadian system of Arabidopsis thaliana includes feedback loops of gene regulation that generate 24-hour oscillations. Components of these loops remain to be identified; none of the known components is completely understood, including ZEITLUPE (ZTL), a gene implicated in regulated protein degradation. ztl mutations affect both circadian and developmental responses to red light, possibly through ZTL interaction with PHYTOCHROME B (PHYB). We conducted a large-scale genetic screen that identified additional clock-affecting loci. Other mutants recovered include eleven new ztl alleles, encompassing mutations in each of the ZTL protein domains. Each mutation lengthened the circadian period, even in dark-grown seedlings entrained to temperature cycles. A mutation of the LOV/PAS domain was unique in retaining wild-type responses to red light, both for circadian period and in the control of hypocotyl elongation. This uncoupling of ztl phenotypes indicates that interactions of ZTL protein with multiple factors must be disrupted to generate the full ztl mutant phenotype. Protein interaction assays showed that the ztl mutant phenotypes were not fully explained by impaired interactions with previously-described partner proteins ASK1, TOC1 and PHYB. Interaction with PHYB was unaffected by mutation of any ZTL domain. Mutation of the kelch repeat domain affected protein binding at both the LOV/PAS and the F-box domains, indicating that interaction among ZTL domains leads to the strong phenotypes of kelch mutations. Forward genetics continues to provide insight regarding both known and newly-discovered components of the circadian system, though current approaches have saturated mutations at some loci.
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