Mathematical modelling of the light input signalling pathways to the Arabidopsis circadian oscillators

Abstract

Natural light is defined by multiple factors including photoperiod length, intensity, and wavelength, all of which regulate the dynamics of Arabidopsis circadian oscillators. Mechanistically, light regulation of the circadian oscillator occurs through multiple synergistic and/or independent molecular signalling pathways. Physiologically, it manifests as entrainment under periodic environments and as modulation of free-running rhythms under constant conditions. Mathematical modelling provides a systematic approach to studying highly interlocked dynamical systems such as circadian oscillators and the light signalling pathways that regulate them. The structure of Arabidopsis circadian oscillators is well captured by current models but the mechanisms by which entrainment and modulation occur are poorly described, often with light input treated as binary on or off. In this thesis, we developed mathematical models by extending a circadian oscillator model to light signalling pathway components. The new model is capable of performing reliable simulations and predictions of circadian dynamics under various light conditions (photoperiods, intensities, and wavelengths). Systemic analyses were performed in the model to study the mechanisms of light entrainment and modulation and reveal the roles of individual light signalling pathways in circadian entrainment. Parameter plasticity analyses identified key regulatory edges that mediate dynamic plasticity in response to changes in light intensity. These results contribute to a deeper understanding of how light inputs structure circadian timekeeping in Arabidopsis.