Ma, Zisong: Hsp90 mediates temperature regulation on the Arabidopsis circadian clock. - Bonn, 2014. - Dissertation, Rheinische Friedrich-Wilhelms-Universität Bonn.
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author = {{Zisong Ma}},
title = {Hsp90 mediates temperature regulation on the Arabidopsis circadian clock},
school = {Rheinische Friedrich-Wilhelms-Universität Bonn},
year = 2014,
month = aug,

note = {To anticipate rhythmic changes and optimize timing of physiological events, many organisms have evolved an internal-timing mechanism named the circadian clock. In Arabidopsis, its clock system consists of the positive/negative feedback loops, which are formed by oscillating components. The internal circadian rhythm resonates with daily environmental changes. The circadian clock can be set by two major exogenous cues: light and temperature. The clock components CCA1, LHY, PRR7, PRR9, TOC1, GI, and ELF3 are involved in the temperature regulation on the circadian clock, but the detailed mechanism, for how their inputs are processed still remains poorly understood. Hsp90 is one of the most important protein chaperons in living organisms. Hsp90 is intensively involved in the heat-stress response. Therefore, I proposed that Hsp90 participates in clock regulation in Arabidopsis.
In Chapter 3, Hsp90 was genetically and pharmacologically proved to influence the circadian clock. The period length was lengthened in the hsp90.2-3 mutant. Moreover, the phase response assay showed that Hsp90.2 particularly influenced the circadian clock before dawn. A chemical-epitasis assay on clock mutants revealed that CCA1 and LHY were involved in the Hsp90 regulation pathway. Interestingly, I found that the period length was closely related to the transcription patterns of CCA1 and LHY. Furthermore, by using the qRT-PCR approach, I found that PRR9 which represses the transcription of CCA1 was also involved in the Hsp90 regulation pathway. ELF3 was demonstrated to be the transcription repressor of PRR9 and the repression is altered by temperature particularly in the dark. This is consistent with the result of my phase response assay. In microscope assay, I found that Hsp90.2 transferred into the nucleus and co-localized with ELF3. Afterwards, an in vivo protein binding assay showed the interaction between Hsp90.2 and ELF3. Together, I could connect Hsp90.2 to an input at an oscillator component.
In Chapter 4, I examined the clock phenotypes of other hsp90.2 mutants after entrainment to either light or temperature. The hsp90.2-6 and hsp90.2-7 mutation resulted in a longer period under LD conditions whereas hsp90.2-4 and hsp90.2-8 resulted in a shorter period under WC conditions. Together, allele specific effects were detected.
Taken together, my thesis has placed Hsp90 within the clock input pathway. CCA1, LHY, PRR9 and ELF3 were all identified as targets in Hsp90 regulation pathway. Since different hsp90.2 mutations caused different clock phenotype, therefore I propose that more than one input pathways are thought to be present in Arabidopsis.},

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