Modeling the circadian period and phase shifts in tomatoes: low degradation-driven oscillator dynamics under continuous light and temperature

The circadian clock maintains a period close to 24 hours across a broad range of temperatures, achieving stability through temperature compensation of different period lengths. While PSEUDO-RESPONSE REGULATOR7 (PRR7) and PRR9 have established roles in temperature compensation, TIMING OF CAB EXPRESSION 1 (TOC1, also known as PRR1) are specifically essential for this process at low temperatures. However, their function under high-temperature conditions remains unknown. In this study, we develop a tomato circadian clock model incorporating continuous light and temperature inputs to better approximate natural environmental conditions. Our kernel modeling demonstrates that TOC1 serves as the primary regulator of LHY. Simulations under continuous light conditions yield transcriptional profiles that aligned more closely with experimental data than those using abrupt light transitions. We further examine system dynamics under both isolated light inputs and combined light-temperature conditions. Under constant light, reduced degradation rates of TOC1 perturb circadian homeostasis, inducing both monostable and multistable states. Temperature-mediated regulation of TOC1 degradation enzymes means that decreased mRNA degradation destabilizes the system. Diminished degradation rates of core circadian components can lead to arrhythmicity, while reduced gene degradation shortens the diurnal period and causes phase advances. In integrated light-temperature cycles, the clock maintains robust stability across physiological temperature ranges, with minimal impact from degradation rate variations, exhibiting remarkable robustness of the model.