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The contribution of plastic circadian period to circadian entrainment and plant performance

Supervisor: Alex Webb (Plant Sciences)

It is a common misconception that circadian oscillators have a period of 24 h, but circadian period is not fixed, circadian period can vary widely from 20 – 35 h (Roenneberg et al., 2003; Dodd et al., 2005; 2014). Not only is the period variable, circadian period has a dynamic plasticity because the circadian oscillator can respond to environmental and metabolic signals by speeding up or slowing down. The molecular pathways and purpose of this dynamic plastic adjustment of circadian period are not known.

In this project you will investigate if this dynamic plasticity of circadian period contributes to the synchronisation of circadian clocks to the environmental cycles of light and dark. You will assess the ability of wild type and mutant plants to entrain to environmental signals by measuring the degree of phase shift induced by light, sucrose and nicotinamide in so called phase response curves (PRC) in constant conditions and the entrained phase in light and dark cycles. By performing these experiments in  mutants, which we have shown already to have altered circadian oscillator period adjustment you will determine if dynamic circadian oscillator period adjustment is required for entrainment.

The fathers of modern circadian biology advanced two competing theories for entrainment. Pittendrigh proposed that the circadian oscillator is phase advanced every day in a discrete non-parametric process that is discontinuous. Aschoff, on the other hand, considered entrainment as a continuous parametric process in which the circadian oscillator period is plastic, with the oscillator accelerating and decelerating to keep in synchronisation with environmental light and dark cycles.

We will directly test Aschoff’s classic model of entrainment, in which dynamic adjustment of circadian period contributes to entrainment, by analysing changes in cycle period over time using a Poincaré analysis we have developed. If plastic circadian period contributes to entrainment as proposed by Aschoff, you will observe continuous dynamic adjustment of the oscillator period during entrainment. If not this will support the counter hypothesis of Pittendrigh’s in which the circadian system has a fixed period that is subject to rapid advances or delay of phase in response to the entrainment stimulus.

A successful outcome of this programme will be a breakthrough in circadian biology.

More studentships in the Webb lab and background information.