Received November 22, 2005
Returned for revision December 22, 2005
Accepted January 26, 2006
Analysis of phase of LUCIFERASE expression reveals novel circadian quantitative trait loci in Arabidopsis
Chiarina Darrah , Bethan L. Taylor , Kieron D. Edwards , Paul E. Brown , Anthony Hall , and Harriet G. McWatters *
Department of Plant Sciences, University of Oxford, South Parks Road, Oxford, OX1 3RB, UK
Institute of Molecular Plant Sciences, University of Edinburgh, Mayfield Road, Edinburgh, EH9 3JH, UK
School of Biological Sciences, Biosciences Building, Crown Street, University of Liverpool, L69 7ZB, UK
* Corresponding author; email: Harriet.McWatters{at}plants.ox.ac.uk.
In response to exogenous rhythms of light and temperature, most organisms exhibit endogenous circadian rhythms; i.e. cycles of behaviour and gene expression with a periodicity of
24hrs. One of the defining characteristics of the circadian clock is its ability to synchronise (entrain) to an environmental rhythm. Entrainment is arguably the most salient feature of the clock in evolutionary terms. Previous quantitative trait studies of circadian characteristics in Arabidopsis thaliana considered leaf movement under constant (free-running) conditions. This study, however, addressed the important circadian parameter of phase, which reflects the entrained relationship between the clock and the external cycle. Here it is shown that, when exposed to the same photoperiod, Arabidopsis accessions differ dramatically in phase. Variation in the timing of circadian LUCIFERASE expression was used to map loci affecting the entrained phase of the clock in a recombinant population derived from two geographically distant accessions, Landsberg erecta and Cape Verde Islands. This is the first time a reporter gene construct has been used to map a quantitative trait. Four quantitative trait loci (QTL) were found with major effects on circadian phase. A QTL on chromosome 5 contained SRR1 and PRR3, both genes known to affect the circadian clock. Previously unknown polymorphisms were found in both genes making them candidates for the effect on phase. Fine mapping of two other QTL highlighted genomic regions not previously identified in any circadian screens, indicating their effects are likely to be due to genes not hitherto considered part of the circadian system.