|dc.description.abstract||The Arabidopsis thaliana circadian clock is involved in regulating several plant systems
including light signalling, germination and the cold signalling pathway. The role of the
circadian clock in regulating far-red and red light induced dormancy and germination,
however, is not well understood. In this thesis it is shown that the circadian clock does
not seem to be involved in regulating far-red light induction of dormancy, but that the
TIMING OF CAB EXPRESSION 1 (TOC1) gene is vital for red light induced
germination to occur.
In Arabidopsis thaliana, the transcription factors, C-REPEAT BINDING FACTORs
(CBFs) are key components of the cold acclimation pathway. The expression of the
CBFs has recently been shown to be regulated by the circadian clock; however, our
understanding of how the CBFs are regulated by the clock is far from complete.
In the main focus of this thesis a systems biology approach was utilised to try and
better understand the circadian regulation of plant cold responses, specifically the
manner by which the circadian clock regulates the cold acclimation pathway
C-REPEAT BINDING FACTOR 3 (CBF3) gene. Freezing tolerance assays were
carried out to increase our knowledge of the clock regulation of the cold signalling
pathway. Circadian clock mutant lines without previously reported freezing tolerance
phenotypes were identified in the TOC1 mutant, toc1-101, and the EARLY
FLOWERING 3 (ELF3) and LUX ARRHYTHMO (LUX) mutants elf3-1 and lux.
The freezing assay data was used to influence model designs for the circadian
regulation of CBF3 expression. Several potential models of CBF3 regulation were
created. The models were then optimised against publically available microarray gene
expression data. Model selection using a Corrected Akaike Information Criterion
(AICc) was utilised to establish models that best fit biological data. Predictions made
by the models were then tested, thus leading to the establishment of new circadian
clock mechanisms of CBF3 being discovered.
The modelling procedure predicted the involvement of the Evening Complex (EC) and
TOC1 in regulating CBF3 expression as well as the already reported regulation by
LATE ELONGATED HYPOCOTYL (LHY) and CIRCADIAN CLOCK
ASSOCIATED1 (CCA1); the PSEUDO-RESPONSE REGULATORS (PRRs) which
had been predicted as direct regulators of the CBFs were not needed to produce
correct CBF3 expression in any of the potential models.
The direct TOC1 and Evening Complex regulation of CBF3 promotion was then
confirmed by chromatin immunoprecipitation.||en_GB