The singularity response reveals entrainment properties of the plant circadian clock

Abstract

Circadian clocks allow organisms to synchronize their physiological processes to diurnal variations. A phase response curve allows researchers to understand clock entrainment by revealing how signals adjust clock genes differently according to the phase in which they are applied. Comprehensively investigating these curves is difficult, however, because of the cost of measuring them experimentally. Here we demonstrate that fundamental properties of the curve are recoverable from the singularity response, which is easily measured by applying a single stimulus to a cellular network in a desynchronized state (i.e. singularity). We show that the singularity response of Arabidopsis to light/dark and temperature stimuli depends on the properties of the phase response curve for these stimuli. The measured singularity responses not only allow the curves to be precisely reconstructed but also reveal organ-specific properties of the plant circadian clock. The method is not only simple and accurate, but also general and applicable to other coupled oscillator systems as long as the oscillators can be desynchronized. This simplified method may allow the entrainment properties of the circadian clock of both plants and other species in nature.

Unstable Phase Response Curves Shown by Spatiotemporal Patterns in the Plant Root Circadian Clock

“…These results indicate that the PRCs for thermal stimuli depend on their magnitude; the PRCs asymmetrically changed from positive to negative temperature stimuli. These changes are consistent with a previous study (Masuda et al, 2021). The PRCs in CCA1 were the opposite phase to those in TOC1 , as CCA1 and TOC1 oscillate in opposing phases.…”

“…Therefore, our results indicated that there were small differences between CCA1 and TOC1 in root PRCs. On the contrary, previous studies have reported PRC differences for temperature stimuli between genes in individual roots (Michael et al, 2003a;Masuda et al, 2021). In these studies, PRC was measured under constant light conditions, and in the present study, it was measured under constant dark conditions.…”

“…We measured the PRCs thermal stimuli (30 min pulses, ±3 and ±10 C) because temperature change is the primal zeitgeber for plant roots. We compared the root PRCs for thermal stimuli in CCA1 and TOC1 because a previous study reported differences in the PRC for thermal stimuli in different clock genes (Michael et al, 2003a; Masuda et al, 2021). We also confirmed that changes in the PRC depend on the amplitude of circadian rhythms, as reported previously (Masuda et al, 2017).…”

Principles, mechanisms and functions of entrainment in biological oscillators

“…phase singularities), impact the propensity for entrainment [1] (box 2). A system's PRCs can change by varying the amplitude or duration of the external pulse [54]. Stable entrainment of NF-κB oscillators (figure 2f ) requires a minimal duration and minimal concentration of the synchronizing TNF pulse [55].…”

Circadian entrainment in Arabidopsis

“…A single pulse of entraining stimuli is applied, which resynchronizes the oscillators. Because the resynchronization of multiple desynchronized oscillators involves adjustment from all possible phases, it is possible to mathematically reconstruct the PRC from one treatment at one time point, and therefore this recently described approach, while conceptually complex, has the advantage of reduced experimentation ( Masuda et al, 2021 ).…”