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Query: UMLS:C0009443 (cold)
 92,137 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

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.
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PMID:Two Arabidopsis circadian oscillators can be distinguished by differential temperature sensitivity. 1273 79

In plants, the circadian clock is implicated in the biological system that generates diurnal oscillations in cellular and physiological activities. The circadian clock must be synchronized (or entrained) to local time by environmental time cues, such as light/dark and/or hot/cold cycles. In Arabidopsis thaliana, although a number of clock-associated components have been uncovered over the last decade, the clock-associated elements that are involved in entrainment to environmental time cues are largely unknown. In this regard, we have been characterizing one core group of clock components that together control the pace of the central oscillator, including PSEUDO-RESPONSE REGULATOR9 (PRR9), PRR7, PRR5 and TIMING OF CAB2 EXPRESSION 1 (TOC1; or PRR1). The primary aim of this study is to clarify whether these PRR members are implicated in entrainment of the circadian clock to environmental time cues. For this purpose, the diurnal oscillation profiles of clock-controlled genes in the presence of environmental time cues were determined in a set of prr mutants, including a prr9 prr7 prr5 toc1 quadruple mutant. As an extreme phenotype, the prr9-10 prr7-11 prr5-11 toc1-2 quadruple mutant showed an arrhythmia phenotype even under light/dark and hot/cold cycles. In contrast, a cca1-1 lhy-11 toc1-2 triple mutant maintained robust oscillations in the presence of these environmental time cues, although their phases were markedly affected. Based on these results, we propose that the clock components PRR9, PRR7 and PRR5 together might represent elements necessary for the circadian clock to entrain properly to local time in response to light/dark and hot/cold cycles in natural habitats.
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PMID:Involvement of Arabidopsis clock-associated pseudo-response regulators in diurnal oscillations of gene expression in the presence of environmental time cues. 1901 37