Imbibition, but Not Release from Stratification, Sets the Circadian Clock in Arabidopsis Seedlings

Zhong, Hai Hong; Painter, Janet E.; Salome, Patrice A.; Straume, Martin; McClung, C. Robertson

doi:10.2307/3870780

Cited by 20 publications

(38 citation statements)

References 39 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…However, we were unable to address whether clock genes such as CCA1, LHY, and TOC1 were themselves cycling in etiolated seedlings. In addition, the timing of the first circadian oscillation could not be deduced from our results; at best, we could conclude that the onset of circadian rhythmicity in etiolated seedlings occurs within 10 d after hydration of the seed (Zhong et al, 1998).…”

contrasting

confidence: 68%

“…We sought to resolve the apparent contradiction between the observations of Kikis et al (2005) and our earlier work (Zhong et al, 1998) by directly monitoring gene expression in etiolated seedlings. By far the most studied circadian clock-controlled gene in Arabidopsis is LHCB1*1 (e.g.…”

mentioning

confidence: 89%

“…We previously inferred that a circadian system is running in etiolated seedlings maintained in the dark for 10 d (Zhong et al, 1998). Although we were unable to observe oscillations in the clock-controlled CAT2 or CAT3 steadystate mRNA levels in etiolated wild-type seedlings (Zhong et al, 1994(Zhong et al, , 1997(Zhong et al, , 1998, we observed a circadian rhythm in the amplitude of the acute induction of CAT2 mRNA in response to light (Zhong et al, 1998). From this, we deduced that a circadian clock must be running in etiolated seedlings and gating the acute induction of CAT2 mRNA by light.…”

mentioning

confidence: 99%

See 2 more Smart Citations

Circadian Timekeeping during Early Arabidopsis Development

2008

Self Cite

View full text Add to dashboard Cite

The circadian coordination of organismal biology with the local temporal environment has consequences for fitness that may become manifest early in development. We directly explored the development of the Arabidopsis (Arabidopsis thaliana) clock in germinating seedlings by monitoring expression of clock genes. Clock function is detected within 2 d of imbibition (hydration of the dried seed). Imbibition is sufficient to synchronize individuals in a population in the absence of entraining cycles of light-dark or temperature, although light-dark and temperature cycles accelerate the appearance of rhythmicity and improve synchrony among individuals. Oscillations seen during the first 2 d following imbibition are dependent on the clock genes LATE ELONGATED HYPOCOTYL, TIMING OF CAB EXPRESSION1, ZEITLUPE, GIGANTEA, PSEUDO-RESPONSE REGULATOR7 (PRR7), and PRR9, although later circadian oscillations develop in mutants defective in each of these genes. In contrast to circadian rhythmicity, which developed under all conditions, amplitude was the only circadian parameter that demonstrated a clear response to the light environment; clock amplitude is low in the dark and high in the light. A circadian clock entrainable by temperature cycles in germinating etiolated seedlings may synchronize the buried seedling with the local daily cycles before emergence from the soil and exposure to light.

show abstract

contrasting

confidence: 68%

mentioning

confidence: 89%

mentioning

confidence: 99%

See 1 more Smart Citation

Circadian Timekeeping during Early Arabidopsis Development

2008

Self Cite

View full text Add to dashboard Cite

show abstract

“…In our experiments, we imbibe (hydrate) the seeds and then stratify at 4°C in the dark to synchronize germination before release into light at 22°C. We have previously shown that the phase of morning-specific CAT2 transcript is set by imbibition and fails to respond to the subsequent temperature step and͞or light onset associated with release from stratification (26). Therefore, we tested whether CAB2::LUC and CAT3::LUC are equally responsive to imbibition and unresponsive to release from stratification and͞or light onset.…”

Section: Resultsmentioning

confidence: 99%

Two Arabidopsis circadian oscillators can be distinguished by differential temperature sensitivity

Michael

Salomé

McClung

2003

Proc. Natl. Acad. Sci. U.S.A.

Self Cite

139

138

View full text Add to dashboard Cite

Circadian rhythms are widespread in nature and reflect the activity of an endogenous biological clock. In metazoans, the circadian system includes a central circadian clock in the brain as well as distinct clocks in peripheral tissues such as the retina or liver. Similarly, plants have distinct clocks in different cell layers and tissues. Here, we show that two different circadian clocks, distinguishable by their sensitivity to environmental temperature signals, regulate the transcription of genes that are expressed in the Arabidopsis thaliana cotyledon. One oscillator, which regulates CAB2 expression, responds preferentially to light-dark versus temperature cycles and fails to respond to the temperature step associated with release from stratification. The second oscillator, which regulates CAT3 expression, responds preferentially to temperature versus light-dark cycles and entrains to the release from stratification. Finally, the phase response curves of these two oscillators to cold pulses are distinct. The phase response curve of the oscillator component TOC1 to cold pulses is similar to that of CAB2, indicating that CAB2 is regulated by a TOC1-containing clock. The existence of two clocks, distinguishable on the basis of their sensitivity to temperature, provides an additional means by which plants may integrate both photoperiodic and temperature signals to respond to the changing seasons. T he circadian clock is an endogenous oscillator with an approximate period of 24 hr that can be synchronized, or entrained, to the exact period of daily oscillations in light and temperature (1). This enables an organism to phase its biological activities to the correct time of day. The sleep-wake cycle in humans, activity and eclosion rhythms in flies, and conidiation in Neurospora are rhythmic processes that display distinct phase angles with the environment (2). In the flowering plant Arabidopsis thaliana, the circadian clock phases the peak mRNA abundance of many genes to distinct times of day (3). Furthermore, the phase angle of specific circadian rhythms with the environmental light-dark (LD) cycle controls seasonal behavior such as flowering (4-6).The clock is temperature-compensated, meaning that the pace of the clock is more or less constant across a range of temperatures and fails to exhibit the acceleration with temperature that characterizes typical enzymatic reactions. Nonetheless, temperature serves as an important environmental time cue and entrainment to temperature cycles has been demonstrated in a number of systems (7,8). It is commonly assumed that light is the dominant environmental time cue for circadian clocks, although few studies have systematically compared light and temperature (9-12). In fact, temperature cycles applied antiphase to LD cycles set the phase angle of multiple rhythms, including CO 2 assimilation in Kalanchoë (13), ethylene production in sorghum (14), and conidiation in Neurospora (15).We compared the relative strengths of temperature cycles and LD cycles as determinants of the ph...

show abstract

“…S5). This could be caused by circadian oscillations, synchronized by either imbibition (Zhong et al, 1998) or stratification (Michael et al, 2003a), that were not actively considered or synchronized between experiments. In addition, strong phase-specific effects are seen for unknown reasons in experiment C, which also used continuous light.…”

Section: Discussion Circadian and Diurnal Regulation Cause Variation mentioning

confidence: 99%

Disruption of the Arabidopsis Circadian Clock Is Responsible for Extensive Variation in the Cold-Responsive Transcriptome

et al. 2008

View full text Add to dashboard Cite

In plants, low temperature causes massive transcriptional changes, many of which are presumed to be involved in the process of cold acclimation. Given the diversity of developmental and environmental factors between experiments, it is surprising that their influence on the identification of cold-responsive genes is largely unknown. A systematic investigation of genes responding to 1 d of cold treatment revealed that diurnal-and circadian-regulated genes are responsible for the majority of the substantial variation between experiments. This is contrary to the widespread assumption that these effects are eliminated using paired diurnal controls. To identify the molecular basis for this variation, we performed targeted expression analyses of diurnal and circadian time courses in Arabidopsis (Arabidopsis thaliana). We show that, after a short initial cold response, in diurnal conditions cold reduces the amplitude of cycles for clock components and dampens or disrupts the cycles of output genes, while in continuous light all cycles become arrhythmic. This means that genes identified as cold-responsive are dependent on the time of day the experiment was performed and that a control at normal temperature will not correct for this effect, as was postulated up to now. Time of day also affects the number and strength of expression changes for a large number of transcription factors, and this likely further contributes to experimental differences. This reveals that interactions between cold and diurnal regulation are major factors in shaping the cold-responsive transcriptome and thus will be an important consideration in future experiments to dissect transcriptional regulatory networks controlling cold acclimation. In addition, our data revealed differential effects of cold on circadian output genes and a unique regulation of an oscillator component, suggesting that cold treatment could also be an important tool to probe circadian and diurnal regulatory mechanisms.

show abstract

Imbibition, but Not Release from Stratification, Sets the Circadian Clock in Arabidopsis Seedlings

Cited by 20 publications

References 39 publications

Circadian Timekeeping during Early Arabidopsis Development

Circadian Timekeeping during Early Arabidopsis Development

Two Arabidopsis circadian oscillators can be distinguished by differential temperature sensitivity

Disruption of the Arabidopsis Circadian Clock Is Responsible for Extensive Variation in the Cold-Responsive Transcriptome

Contact Info

Product

Resources

About