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Phase oscillator models of circadian regulation by metabolites

Supervisors: Alex Webb (Plant Sciences) with Professor Akiko Satake (Hokkaido University, Japan)

The 24 h circadian clock is major regulator of plant growth, but the mechanisms by which circadian clocks regulate biomass accumulation are unknown. Recently Webb demonstrated that photosynthetically-derived sugars adjust the phase and entrain the plant circadian clock through a metabolic dawn (Nature 502, 689–692). Independently, Satake proposed a mathematical model that demonstrates a measure of carbon availability adjusts the phase of the circadian clock, resulting in turn to an adjustment of carbon metabolism (Frontiers in Plant Science 3, 2012). We will combine these findings from experimental and theoretical studies to obtain new understanding of how plants regulate growth. We specifically address two questions. 1) Why the plant circadian clock has evolved a characteristic response to sugars.   2) What is the role of circadian regulation of carbon metabolism in the control of plant growth. Satake will perform model development and analyses. Webb will develop new approaches to capture dynamical growth rates and test hypotheses arising from the theoretical studies.

The project has experimental and theoretical aspects. We will measure the dynamics of the circadian clock and growth to inform the theory and test generated hypotheses. Circadian rhythms will be measured by imaging of clock gene activity, delayed chlorophyll fluorescence and growth (leaf and root elongation). We will build an automated  growth measurement array using Raspberry Pi mini PCs and CCD cameras.

We will develop in collaboration with Professor Satake a multi-scale mathematical model in which starch and sucrose are a function of photosynthetic carbon assimilation, degradation of starch to sucrose, and sucrose transport. These processes will be considered regulated by the clock. In the model, a feedback between the clock and carbon metabolism will be achieved by a requirement to minimise carbon starvation through phase adjustment of circadian starch degradation. Carbon starvation penalises values below a critical threshold level of sucrose at which there is starvation and growth ceases. The new data will be integrate Webb’s new data into the model to investigate why the plant circadian clock has evolved a characteristic response to sugars?

More studentships in the Webb lab and background information.