Physiological and Genetic Dissection of Sucrose Inputs to the Arabidopsis thaliana Circadian System

Abstract

Circadian rhythms allow an organism to synchronize internal physiological responses to the external environment. Perception of external signals such as light and temperature are critical in the entrainment of the oscillator. However, sugar can also act as an entraining signal. In this work, we have confirmed that sucrose accelerates the circadian period, but this observed effect is dependent on the reporter gene used. This observed response was dependent on sucrose being available during free-running conditions. If sucrose was applied during entrainment, the circadian period was only temporally accelerated, if any effect was observed at all. We also found that sucrose acts to stabilize the robustness of the circadian period under red light or blue light, in addition to its previously described role in stabilizing the robustness of rhythms in the dark. Finally, we also found that CCA1 is required for both a short- and long-term response of the circadian oscillator to sucrose, while LHY acts to attenuate the effects of sucrose on circadian period. Together, this work highlights new pathways for how sucrose could be signaling to the oscillator and reveals further functional separation of CCA1 and LHY.

Chemical Perturbation of Chloroplast-Related Processes Affects Circadian Rhythms of Gene Expression in Arabidopsis: Salicylic Acid Application Can Entrain the Clock

“…For the experiments presented in Figures 3A,B, the plants harboring GI:LUC construct were entrained for 5 days under 12-h light/12h dark photoperiod at a constant temperature of 22 • C before entering continuous darkness at dusk. This was similar to the carbon and sucrose examinations by Perea-García et al (2015); Perea-Garcia et al (2016), and Philippou et al (2019). Briefly, every 3 h, a subset of plants was retrieved from the basal growth medium (MS) and subjected to non-parametric entrainment with 3-h light pulses (WL) on the growth medium that contained SA at 1 mM or DMSO.…”

“…It is noteworthy that, under red light (Figure 5C), the toc1-21 mutant exhibited a long period phenotype, whereas under BL we recorded a short period phenotype of the toc1-21 mutant ( Figure 5D and Supplementary Table S23), which was not affected by SA application. Previously, we have shown that the lhy-21, cca1-11, and gi-11 mutants also show sucrose-dependent phenotypes (Philippou et al, 2019).…”

Cryptochromes integrate green light signals into the circadian system

“…Exogenous sucrose has previously been used to saturate plants' circadian responses to photoassimilates (Frank et al, ; Haydon et al, ; Haydon et al, ; Philippou et al, ). Interestingly, exogenous sucrose was sufficient to mask the cry1 circadian defect under constant green light but not constant blue light (Figures c and S4b).…”

“…Interpretation of light signalling into the circadian system is complicated by the clock's response to metabolites derived from photosynthesis (Frank et al, ; Haydon et al, ; Haydon et al, ; Philippou et al, ). In order to assess the contribution of photosynthesis towards circadian rhythmicity under constant green light, we assessed circadian rhythms in the presence of CO 2 ‐depleted air (Figures d and ).…”

“…Although our data suggest a role for cryptochromes in green light perception, recent work has emphasized the contribution of photoassimilates to circadian timing (Frank et al, 2018;Haydon et al, 2013;Haydon et al, 2017;Philippou, Ronald, Sanchez-Villarreal, Davis, & Davis, 2019). In order to assess the contribution of photosynthesis towards circadian rhythmicity under constant green light, we assessed circadian rhythms in the presence of CO 2 -depleted air, and/or by supplying exogenous sucrose within the growth media to saturate the cellular response to photosynthetically derived sucrose ( Figures 2d and 4).…”