Characterizing The Circadian Clock In Natural Settings

Circadian clocks regulate endogenous repeating rhythms of approximately 24 hours in duration. Occurring in organisms as diverse as Archea, Bacteria, and Eukaryotes, this phylogenetic ubiquity suggests that the clock modulates the expression of traits critical to fitness. However, no studies in plants have explicitly demonstrated the adaptive significance of naturally occurring quantitative variation in the clock in ecologically relevant settings.

Current models suggest three major components to the clock: the input pathway, the oscillator, and output pathway. The input pathway “sets” the clock, that is, rhythms are entrained to local conditions. After entrainment, the oscillator maintains cycling of the clock, even in the absence of further inputs. Lastly, the output modulates the expression of circadian-regulated processes. Studies in controlled settings suggest that the most prevalent environmental cues involved in entrainment are temperature and quantity and quality of light; however, no studies have quantified the relevance of different inputs in natural settings, or the extent to which annotated loci contribute to quantitative variation among accessions in clock behavior in natural settings.

The overarching objective is to test the adaptive significance and quantify the genetic architecture of clock sensitivity to seasonally variable natural settings. In a series of experiments, we raised transgenic GI::LUC accessions in field settings as well as related NILs; we observe significant variation among accessions in responsiveness to season, and NILs identify genomic regions conferring clock sensitivity to season. Further, quantitative variation in clock parameters are associated with fitness, and these correlations are confirmed in clock mutants, NILs, and long-term evolution studies.