Abstract
BackgroundThe circadian system drives pervasive biological rhythms in plants. Circadian clocks integrate endogenous timing information with environmental signals, in order to match rhythmic outputs to the local day/night cycle. Multiple signaling pathways affect the circadian system, in ways that are likely to be adaptively significant. Our previous studies of natural genetic variation in Arabidopsis thaliana accessions implicated FLOWERING LOCUS C (FLC) as a circadian-clock regulator. The MADS-box transcription factor FLC is best known as a regulator of flowering time. Its activity is regulated by many regulatory genes in the "autonomous" and vernalization-dependent flowering pathways. We tested whether these same pathways affect the circadian system.ResultsGenes in the autonomous flowering pathway, including FLC, were found to regulate circadian period in Arabidopsis. The mechanisms involved are similar, but not identical, to the control of flowering time. By mutant analyses, we demonstrate a graded effect of FLC expression upon circadian period. Related MADS-box genes had less effect on clock function. We also reveal an unexpected vernalization-dependent alteration of periodicity.ConclusionThis study has aided in the understanding of FLC's role in the clock, as it reveals that the network affecting circadian timing is partially overlapping with the floral-regulatory network. We also show a link between vernalization and circadian period. This finding may be of ecological relevance for developmental programing in other plant species.
Highlights
The circadian system drives pervasive biological rhythms in plants
Dose-dependent effect of FLOWERING LOCUS C (FLC) on circadian period FLC RNA abundance correlates with repression of flowering time and quantitatively mediates the vernalization response of flowering time [15]
When we tested for circadian period, the svp mutant showed a significant lengthening in period of 0.7 h compared to wild type (τ = 25.15 ± 0.25 h vs. 24.44 ± 0.17 h, P = 0.006) (Figure 2 and 5, Table 2), in contrast to the significantly shortened circadian period of the flc mutant. These results indicate that FLC may have a unique function in shortening the circadian period of Arabidopsis, which is not shared by other MADS box transcription factors that function in the flowering-time pathways
Summary
The circadian system drives pervasive biological rhythms in plants. Circadian clocks integrate endogenous timing information with environmental signals, in order to match rhythmic outputs to the local day/night cycle. Most eukaryotes and some prokaryotes have evolved a circadian clock to adapt to the 24 h day/night cycle These clocks drive biological rhythms in many aspects of metabolism, physiology, and behavior, all with a period close to 24 h [1]. In Arabidopsis, there is emerging evidence that a set of about 20 genes create one, or more, feedback circuits (the 'circadian oscillator') to generate the 24 h period [2,6], and this rhythmically regulates the level of around 6% of transcripts [7] Circadian clocks, including those of Arabidopsis, are reset by light and temperature signals in a characteristic fashion that entrains the clock to the local time in its environment [6]. Whereas the mechanisms of photic entrainment are being elucidated [2,6], those governing temperature entrainment and temperature compensation remain to be determined
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