Analysis of the circadian clock at the single cell level in a multi-cellular context.

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One of the most important adaptations to living on the Earth is to the daily fluctuation in light. To cope with this, from simple prokaryotes to complex multicellular life like ourselves, organisms have evolved an endogenous timer, the circadian clock. Circadian clocks allow an organism to time activities and processes so that they occur at the optimum time of day. The clock also allows an organism to measure day length, and thus the seasons and to alter its biology accordingly. It is not surprising, therefore, that the circadian clock affects a huge range of biological processes. In plants, this includes key agricultural traits such as flowering time, dormancy, water use efficiency, nitrogen metabolism and yield. In the long term our work on the circadian clock is likely to inform and impact the development of new crop cultivars. Our current understanding of the circadian clock is largely based on experiments on whole plants or groups of plants. Over the years, a combination of mathematical modelling and whole plant experiments have led to striking breakthroughs in our understanding of the clock components and how they fit together. Mathematical models provide a conceptual framework allowing us to test ideas and understand how different components of the circadian clock interact. However, this body of work has a critical problem. It assumes that every cell in a plant has a clock that behaves identically. Experimental evidence contradicts this idea, but until recently we have not had the tools to analyse the clock in single plant cells.At Liverpool University, using live-cell imaging approaches pioneered for mammalian cell work, we have recently developed a method to monitor the clock in single cells across a living seedling. In this project we will survey the circadian clock with cellular resolution. Then, in collaboration with experts in circadian modelling and single cell analysis at the Sainsbury Laboratory, Cambridge, we will extract important information from this single cell data and build cell-type specific mathematical models. These models will be tested with further experiments, and will answer long-standing questions in circadian biology, such as how do clock networks vary between cell-types? And are there multiple oscillators in a single cell? Finally we will extend our models into a multicellular context, and use them to direct experiments to investigate how networks are coupling between cells, and how this affects rhythms in the whole plant.