Natural Allelic Variation in the Temperature-Compensation Mechanisms of the Arabidopsis thaliana Circadian ClockSequence data from this article have been deposited with the EMBL/GenBank Data Libraries under accession nos. AY685131 and AY685132.

Abstract

Temperature compensation is a defining feature of circadian oscillators, yet no components contributing to the phenomenon have been identified in plants. We tested 27 accessions of Arabidopsis thaliana for circadian leaf movement at a range of constant temperatures. The accessions showed varying patterns of temperature compensation, but no clear associations to the geographic origin of the accessions could be made. Quantitative trait loci (QTL) were mapped for period and amplitude of leaf movement in the Columbia by Landsberg erecta (CoL) and Cape Verde Islands by Landsberg erecta (CvL) recombinant inbred lines (RILs) at 12Њ, 22Њ, and 27Њ. Six CvL and three CoL QTL were located for circadian period. All of the period QTL were temperature specific, suggesting that they may be involved in temperature compensation. The flowering-time gene GIGANTEA and F-box protein ZEITLUPE were identified as strong candidates for two of the QTL on the basis of mapping in near isogenic lines (NILs) and sequence comparison. The identity of these and other candidates suggests that temperature compensation is not wholly determined by the intrinsic properties of the central clock proteins in Arabidopsis, but rather by other genes that act in trans to alter the regulation of these core proteins.

The Molecular Basis of Temperature Compensation in the Arabidopsis Circadian Clock

“…The lhy mutant, therefore, has a shorter period than cca1 (Student's t test, P < 0.01) at 278C, supporting a role for LHY in the temperature compensation mechanism. This was suggested previously by analysis of natural genetic variation (Edwards et al, 2005), as LHY was noted as a candidate gene for the temperature-specific QTL PerCv1a and PerCola. At 128C, the period of the wild type (23.3 h) differed from that of lhy (21.6 h) by 1.7 h. In cca1, however, the rhythm of CAB:LUC expression was dampened ( Figure 5), and the period difference between the wild type (23.3 h) and cca1 (20.0 h) was 3.3 h. This temperature-dependent shortening of the circadian period and the reduction in rhythm robustness almost phenocopied the effect of gi-11 at 128C (Figures 1 and 2).…”

“…Within this region was the flowering-time gene GI. Sequencing GI from Ler and Cvi revealed a number of polymorphisms, two of which resulted in amino acid substitutions (Edwards et al, 2005). This, together with the period effects of the gi mutant (Park et al, 1999), confirmed GI as a strong candidate for a gene involved in the temperature compensation mechanism.…”

“…The genes underlying some of these, such as the flowering regulator FLOWERING LOCUS C (Edwards et al, 2006), had no known function in the Arabidopsis clock mechanism. By contrast, further characterization of one of these QTL, PerCv1b, identified GI as a candidate for the PerCv1b trait (Edwards et al, 2005).…”

Plant Circadian Rhythms

“…Considerable natural variation in temperature compensation has been described, and GI has been identified as a quantitative trait locus responsible for a substantial portion of that variation (Edwards et al, 2005). It seems likely that this clock property will prove amenable to forward and reverse genetic approaches.…”

“…In Arabidopsis, there is considerable circadian variation among natural genotypes (for examples, see Swarup et al, 1999;Edwards et al, 2005). There is a positive correlation between period length of a set of natural accessions and daylength encountered at latitude of origin of the accessions , which may indicate a selection of altered clock function under differing environmental conditions (temperature and daylength covary with latitude).…”