From a Repressilator-Based Circadian Clock Mechanism to an External Coincidence Model Responsible for Photoperiod and Temperature Control of Plant Architecture inArabodopsis thaliana

Abstract

Circadian clocks enable organisms to define subjective time, that is, to anticipate diurnal day and night cycles. Endogenous circadian rhythms regulate many aspects of an organism's physiological and morphological growth and development. These daily oscillations are synchronized to the environment by external cues such as light and temperature, resulting in enhanced fitness and growth vigor in plants. Recent findings concerning biochemical properties of central oscillators in Arabidopsis thaliana have advanced our understanding of circadian clock function. Central oscillators are composed of three classes of transcriptional repressors. The interactions among them include a repressilator structure. Output from the circadian clock is transduced through regulating transcription of downstream genes directly by the oscillator components. The essential role of the output pathway in the circadian system is to make different elementary steps responsible for daily cellular processes exert maximum effects at specific times of the day. Recently, significant progress was made in defining the mechanisms by which plant growth on a day-to-day basis is activated at specific times of the day in a manner dependent on photoperiod and temperature conditions. Plant growth is controlled by the clock through interactions with light and phytohormone signaling. This review focuses on the node that connects clock output to light and phytohormone signaling that coordinates plant growth with rhythmic changes in the environment.

Wheels within wheels: the plant circadian system

“…In addition, light and sucrose control PIF protein stability: PHYB promotes PIF4 and PIF5 degradation under red light [63], whereas high sucrose levels stabilize PIF5 [64]. Given that the clock influences phytochrome signaling [55, 65] and sugar metabolism (see below), the circadian system influences PIF4 and PIF5 abundance at multiple levels.…”

Auxin‐mediated plant architectural changes in response to shade and high temperature

“…Interaction with the phytochromes mediates PIF phosphorylation and/or degradation, while inactivation of the phytochromes in low R:FR releases their repression and allows the PIFs to act as transcriptional regulators (Lorrain et al , Li et al ). At elevated temperatures, increased PIF4 expression in the cotyledons has been reported (Koini et al , Stavang et al , Nomoto et al ) especially during the dark period (Nomoto et al ), which leads to increased PIF4 levels (Yamashino ). Whether the rise in PIF4 levels in response to temperature elevation is exclusively a transcriptional response or also includes post‐transcriptional regulation is still debated (Stavang et al , Foreman et al , Kumar et al ).…”

PIFs: Systems Integrators in Plant Development

“…2010; Wang et al, 2012;Casal, 2013;de Wit et al, 2013;KinmonthSchultz et al, 2013;Proveniers and van Zanten, 2013;Shin et al, 2013;Wigge, 2013;Yamashino, 2013). Here, we will discuss evidence that emphasizes the role of PIFs as integrators of diverse signals to modulate plant growth and development to deliver the emerging view that PIFs function as required regulatory factors for growth.…”