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Title: Positioning Ca²⁺ within the circadian signalling network
Author: Hotta, Carlos Takeshi
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2007
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Ca2+ is an important part of many short-term signalling pathways in both plants and animals. As [Ca2+]cyt levels are under circadian control, it is possible that Ca2+ is also used as a component in the circadian signalling pathway. In this thesis, I have tried to position circadian [Ca2+]cyt oscillations in the circadian signalling pathway of Arabidopsis thaliana using a range of genetic and pharmacological tools. Three main approaches were used: the measurement of circadian [Ca2+]cyt oscillations in circadian clock mutants, the use of drugs related to nitric oxide signalling and the overexpression of Ca2+-binding proteins. Using photoreceptors mutants, I show that PHYTOCHROMES and CRYPTOCHROMES modulate the [Ca2+]cyt basal levels independently of the circadian clock. Using lines misexpressing components of the circadian oscillator, I show that circadian [Ca2+]cyt oscillations are controlled by a CCA1/LHY/TOC1 (CIRCADIAN CLOCK ASSOCIATED 1/ LATE ELONGATED HYPOCOTYL/ TIMING OF CAB 1) containing oscillator. However, this oscillator is not the same as the one that controls rhythms of CHLOROPHYL A/B BINDING PROTEIN2 (CAB2) promoter activity as its components are used differently. Pharmacological tools suggest that, while cyclic-ADP ribose (cADPR) may set the pace of the circadian clock, nitric oxide (NO) does not. In short-term Ca2+ signalling, NO regulates [Ca 2+]cyt levels through cADPR but not in circadian clock signalling. A separation between short-term and circadian signalling is also suggested by the absence of effects of overexpression of Ca2+-binding proteins in circadian [Ca2+]cyt oscillations. The role of circadian [Ca2+]cyt oscillations remain unknown but they may be an input to the clock and be part of the photoperiodic pathway controlling the transition to reproductive growth.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available