臺灣博碩士論文加值系統

植物透過生理時鐘 (circadian clock) 調控許多與日照長短相關的生理反應，例如：光周期長短影響開花時間。目前已知阿拉伯芥之生理時鐘系統是由三個負向迴圈 (negative feedback loops) 所組成，這些迴圈由一天中在不同時間表現的時鐘基因所組成。尋找新的時鐘基因將有助於更進一步了解生理時鐘之運作模式。本論文發現 LWD1 與 LWD2 為兩個新的生理時鐘蛋白質，負責調控光周期開花與生理時鐘之周期長短。
LWD1 與 LWD2 在阿拉伯芥中為同源基因，兩者之蛋白質具有 91.4 % 的相似度。 lwd1 lwd2 雙重突變株具有提早開花的表現型，且概日韻律之周期也有縮短的現象。經由更深入的分析發現，LWD1 與 LWD2 蛋白質在概日韻律 (circadian rhythm) 系統中扮演雙重角色，它們不僅可影響光訊號輸入途徑 (light input pathway)，同時也能調控中心節律器 (central oscillator)。LWD1/2 之基因表現受到概日韻律之調控，其中以 PRR9/7 蛋白質對於調控 LWD1/2 的表現最為重要。反之，PRR9/7/5 基因之表現亦受到 LWD1/2 之調控， LWD1 蛋白質可進入細胞核中，直接與 PRR9、PRR5 以及 TOC1 之啟動子結合並正向調控這些基因的表現。這些研究結果說明 LWD1 與 PRR9 這兩個基因會形成正向的調控迴圈 (positive feedback loop)。此論文首度揭示阿拉伯芥生物時鐘中存在一正向迴圈。未來探討此正向迴圈的運作機制，以及研究它與其它生理時鐘蛋白質之間的相互調控關係，皆將有助於闡明阿拉伯芥生理時鐘的複雜性。

In plants, circadian clock could control day-length-dependent developmental processes such as photoperiodic flowering. The Arabidopsis circadian clock is formed by several negative feedback loops composed of oscillator genes expressing at specific time during a day. The identification of additional clock genes will help to better dissect the complex nature of the circadian clock. Here we show light-regulated WD repeats protein 1 (LWD1) and LWD2 are new clock genes regulating photoperiodic flowering and circadian period length.
LWD1 and LWD2 proteins share 91.4 % identity in amino acid sequence. The lwd1 lwd2 double mutant has an early flowering phenotype, and a short period length for its internal clock under free running condition. Analysis of the lwd1 lwd2 double mutant also revealed that LWD1/2 plays dual functions in the light input pathway and the regulation of the central oscillator. Promoter:luciferase fusion studies showed that transcriptional activities of LWD1/2 are rhythmic and depend on functional PRR9 and PRR7. LWD1/2 is also needed for the expression of PRR9, PRR7 and PRR5. LWD1 is preferentially localized within the nucleus and associates with promoters of PRR9, PRR5 and TOC1 in vivo. Our results support the existence of a positive feedback loop within the Arabidopsis circadian clock. Further mechanistic studies of this positive feedback loop and its regulatory effects on the other clock components will further elucidate the complex nature of the Arabidopsis circadian clock.

中文摘要 I
Abstract II
Table of Contents III
List of Tables V
List of Figures VI
List of Appendices VII
I. Introduction 1
Circadian rhythm 1
Light input pathway 1
Central oscillators 2
Photoperiodic flowering pathway: an example of the circadian output pathways 3
Clock genes often have multiple functions 4
II. Materials and Methods 6
Plant materials and growth conditions 6
beta-glucuronidase (GUS) histochemical staining 6
Determination of flowering time 7
RNA isolation 8
RT-PCR 8
Northern blot analyses 9
Affymetrix ATH1 Genome Array hybridization and data analyses 9
Quantitative RT-PCR (qRT-PCR) 10
Bioluminescence measurement and data analyses 11
LWD1 antigen preparation and antiserum purification 12
Protein extraction and western blot analysis 13
Subcellular localization of LWD1 14
Chromatin immunoprecipitation (ChIP) assay 15
III. Results 17
Expression characterization of LWD1 and LWD2 in Arabidopsis 17
Identification of lwd1 and lwd2 mutants 17
lwd1 lwd2 double mutant has an early flowering phenotype 18
Genes in photoperiodic pathways are differentially regulated in the lwd1 lwd2 double mutant 18
FT is highly expressed in lwd lwd2 under SD condition 19
LWD1/LWD2 set the correct expression phase of circadian related genes 20
LWD1/2 controls the amplitude and period length of the Arabidopsis circadian rhythm under continuous light 21
The amplitude and robustness of the circadian rhythm is affected in lwd1 lwd2 plants under continuous dark 22
LWD1/2 functions in the light input pathway 23
LWD1 and LWD2 promoters are controlled by the circadian clock 23
LWD1/2 promoter activity is largely regulated by PRR9/7 24
LWD1/2 positively regulates PRR9, PRR7 and PRR5 25
LWD1-GFP preferentially localizes in the nucleus 26
LWD1 proteins have a diurnal expression pattern 27
LWD1 associates with the promoters of PRR9, PRR5 and TOC1 27
IV. Discussion 30
LWD1 and LWD2 are new players in Arabidopsis photoperiod sensing 30
LWD1 and LWD2 are new clock components 31
LWD1 and PRR9 constitute a positive feedback loop 32
LWD1 has multiple entry points to the central oscillator in Arabidopsis 33
LWD1/2 plays a dual function in the circadian system 34
Action mechanism of LWD1 35
V. Conclusions and Future Prospects 36
VI. References 38
Tables 48
Figures 54
Appendices 71

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