The integration of environmental and circadian signals to regulate transcription from the chloroplast genome

De Fraine, Tara Saskia (2021) The integration of environmental and circadian signals to regulate transcription from the chloroplast genome. Masters thesis, University of East Anglia.

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Abstract

In plants, circadian oscillations in gene expression and physiology occur with a period of approximately 24 hrs. The coordination of these oscillations with environmental signals ensures appropriate biological responses depending on the time of day and season, presenting a fitness advantage. There are extensive roles for the transcription factors HY5 and HYH in the regulation of gene transcription in response to environmental and circadian signals. SIG5 is multiple stress-responsive and coordinates nuclear and chloroplast gene expression; ATHB17 regulates SIG5 transcription in response to salt stress. The work described in this thesis aimed to investigate roles for HY5/HYH in the signalling pathway to SIG5 and its chloroplast gene target psbD BLRP, and to identify whether ATHB17 regulates SIG5 in response to cold stress. qRT-PCR was used to monitor SIG5 and psbD BLRP transcript accumulation under circadian and diel conditions in mutants of HY5 and HYH. Roles for these transcription factors in the circadian and environmental regulation of chloroplast transcription were confirmed, suggesting redundancy between the two. Analysis of CCA1 relative expression over a circadian timeseries suggested that HY5/HYH act on the amplitude of SIG5 expression downstream of CCA1. Bioluminescence imaging was also used to assess SIG5 promoter activity in mutants of these transcription factors, suggesting regulation of SIG5 promoter activity by HY5/HYH. Furthermore, measurement of SIG5 transcript abundance following cold stress suggested it is unlikely that ATHB17 regulates SIG5 in response to cold. This research highlights the existence of both distinct and overlapping roles for HY5/HYH in regulating SIG5 in response to environmental and circadian cues. However, other factors contribute to the maintenance of SIG5 and psbD BLRP circadian rhythmicity. Therefore, future work should aim to identify these factors, as well as to further understand the distinct and intersecting roles for HY5/HYH in the regulation of SIG5 and psbD BLRP.

Item Type: Thesis (Masters)
Faculty \ School: Faculty of Science > School of Biological Sciences
Depositing User: Chris White
Date Deposited: 11 May 2022 13:59
Last Modified: 11 May 2022 13:59
URI: https://ueaeprints.uea.ac.uk/id/eprint/84994
DOI:

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