Integration of circadian and environmental information during signalling to chloroplasts

  • Dora Cano Ramirez

Student thesis: Doctoral ThesisDoctor of Philosophy (PhD)


The coordination of biological processes with daily and seasonal changes in the environment is important for the survival of photosynthetic organisms such as plants.
A signalling pathway was previously identified that communicates temporal and light quality information from the circadian oscillator to the chloroplast in Arabidopsis thaliana. This signalling mechanism operates through the action of a nuclear encoded protein called SIGMA FACTOR5 (SIG5), which confers promoter specificity to the plastid encoded plastid RNA polymerase (PEP) in the chloroplast where it causes rhythmic transcription of psbD. In Arabidopsis, there are six sigma factors encoded in the nucleus (SIGMA FACTOR1 (SIG1)-SIG6). I conducted structural homology modelling of the six sigma factors to gain insights about their specificity and regulation.
I also identified in the laboratory a novel low-temperature signalling pathway involving SIG5 that underpins optimum plant performance under both low and freezing temperatures. I demonstrated that this pathway increases freezing tolerance and photosynthetic efficiency at low temperatures, identified upstream and downstream regulators of the pathway, and demonstrated close integration with the circadian oscillator. This suggests the pathway is of considerable biological importance in plants and could be targeted to improve crop yields under uncertain climate conditions.
It is in this context that I then investigated if the pathway operates under fluctuating natural conditions (e.g. during the day and across seasons) using Arabidopsis halleri subsp. gemmifera, which is a perennial relative of the annual A. thaliana. The data revealed seasonal differences in the amplitude of gene transcript accumulation in the signalling pathway and further analysis through statistical modelling revealed the major environmental inputs to the pathway under natural fluctuating conditions.
Finally, using the rare algae Aegagropila linnaei (marimo) daily rhythms of buoyancy driven by photosynthesis were found to be a novel output of the circadian oscillator in plants.
Date of Award6 Nov 2018
Original languageEnglish
Awarding Institution
  • The University of Bristol
SupervisorAntony Dodd (Supervisor) & Keara A Franklin (Supervisor)

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