Modulation of environmental responses of plants by circadian clocks

Abstract

Circadian clocks are signalling networks that enhance an organism's relationship with the rhythmic environment. The plant circadian clock modulates a wide range of physiological and biochemical events, such as stomatal and organ movements, photosynthesis and induction of flowering. Environmental signals regulate the phase and period of the plant circadian clock, which results in an approximate synchronization of clock outputs with external events. One of the consequences of circadian control is that stimuli of the same strength applied at different times of the day can result in responses of different intensities. This is known as 'gating'. Gating of a signal may allow plants to better process and react to the wide range and intensities of environmental signals to which they are constantly subjected. Light signalling, stomatal movements and low-temperature responses are examples of signalling pathways that are gated by the circadian clock. In this review, we describe the many levels at which the circadian clock interacts with responses to the environment. We discuss how environmental rhythms of temperature and light intensity entrain the circadian clock, how photoperiodism may be regulated by the relationship between environmental rhythms and the phasing of clock outputs, and how gating modulates the sensitivity of the clock and other responses to environmental and physiological signals. Finally, we describe evidence that the circadian clock can increase plant fitness.

Light Regulation and Daytime Dependency of Inducible Plant Defenses in Arabidopsis: Phytochrome Signaling Controls Systemic Acquired Resistance Rather Than Local Defense

“…No significant differences in bacterial numbers were detected at 1 hpi for leaves of different lines (data not shown). different times of the day can lead to different intensities of a particular plant response, a phenomenon designated as gating (Hotta et al, 2007). It would thus be conceivable that the observed daytime-dependent differences in P. syringae-induced plant defenses result from the circadian rhythm.…”

“…Examples for such genes are Arabidopsis PCC1 (pathogen and circadian controlled 1) and PAL1 (Sauerbrunn and Schlaich, 2004;Rogers et al, 2005). The plant circadian clock maintains a relatively constant period, even in the absence of environmental cues such as light (Hotta et al, 2007). To discriminate between circadian control and light effects, we have therefore conducted the daytime experiment both in continuous darkness and in continuous light (Fig.…”

PRR3 Is a Vascular Regulator of TOC1 Stability in theArabidopsisCircadian Clock

“…Furthermore, mutations in ZTL and overexpression of PRR3 delayed flowering under long days but not short days, indicating that ZTL and PRR3 might be involved in daylength responses (Somers et al, 2000;Murakami et al, 2004). The circadian clock plays a major role in the measurement of daylength, a key factor in the determination of flowering time (Imaizumi and Kay, 2006;Hotta et al, 2007), and the vasculature of the leaves has been shown to be where photoperiodic cues are perceived and integrated to initiate flowering (Takada and Goto, 2003;Endo et al, 2005Endo et al, , 2007. Therefore, the modulation of TOC1 binding to ZTL through the PRR3-TOC1 complex might have an important role in specific clock output, such as flowering and/or the modulation of light perception through TOC1 stability.…”

Global transcriptomic analysis ofCyanothece51142 reveals robust diurnal oscillation of central metabolic processes

“…Circadian behavior, the endogenous oscillation of processes with a period length of Ϸ1 day, is a fundamental aspect of biology that allows organisms to respond to their environment. The circadian clock controls a wide variety of biological activities, including sleep-wake cycles in mammals, leaf movements of plants, conidiation of Neurospora, and bioluminescence in dinoflagellates (1)(2)(3)(4). In contrast, prokaryotes were long thought incapable of daily biological rhythms, because their generation times are typically shorter than a circadian period (5).…”