Project description:Plants trigger leaf senescence to relocate energy and nutrients from aging leaves to developing tissues or storage organs to optimize the growth and reproduction under limited nutrients and energy conditions. Jasmonate signaling is one of the major endogenous hormone signals to induced leaf senescence in Arabidopsis. However, whether circadian clock will gate Jasmonate signaling to induce leaf senescence and the underlying precise mechanism is unclear. Here we find that the Evening Complex (EC) of core oscillator closely regulates leaf senescence. To identify the underlying mechanism of EC regulating leaf senescence, we conducted RNA-sequencing. Transcriptomic data reveals Evening complex extensively involves into JA signal transduction and responses. Moreover, the mutants of ELF3, ELF4 and LUX universly display the accelerated JA-induced leaf senescence phenotype, while their overexpression lines act reversely. In accordance with the transcript levels of JA immediate early induced JA-responsive gene MYC2 are up-regulated in lux mutants. Futhermore we demonstrated LUX can bind to to the promoter of MYC2 in vivo to represses its transcription. In addition, the accelerated JA-induced leaf senescence in mutants of evening complex can be overturned by myc2, myc3 and myc4 mutants redundantly. Collectively, our findings demonstrated the underlying molecular basis for circadian clock gating jasmonate signaling to induce leaf senescence through the module of evening complex to directly repressing MYC2 transcription. This novel established molecular module also refines complicated nodes between circadian clock and jasmonate signal in Arabidopsis.
Project description:In many organisms, the circadian clock is composed of functionally coupled morning and evening oscillators that regulate the bouts of dawn and dusk activity. In Arabidopsis, oscillator coupling relies on a core loop in which the evening oscillator component TOC1 was proposed to activate a subset of morning-expressed oscillator genes. Our systems-biological approach overturns the current view of the Arabidopsis circadian clock showing that TOC1 does not function as an activator but as a timely-controlled general repressor of morning and evening oscillator components. Repression occurs through rhythmic binding to the promoters of all oscillator genes, suggesting a previously unexpected direct connection between the morning and evening loops.
Project description:The plant circadian clock exerts a critical role in the regulation of multiple biological processes including responses to biotic and abiotic stresses. It is estimated that the clock regulates up to 80% of the transcriptome in Arabidopsis, thus understanding the molecular mechanisms that control this rhythmic transcriptome requires identification of the targets of each clock component. The Arabidopsis core clock is partially comprised of a transcriptional regulatory loop between the MYB domain containing transcription factors CIRCADIAN CLOCK ASSOCIATED1 (CCA1) and LATE ELONGATED HYPOCOTYL (LHY), and TIMING OF CAB EXPRESSION1 (TOC1). As a key component of the clock, CCA1 is able to initiate and set the phase of clock-controlled rhythms. CCA1 regulates the transcription of several genes by directly binding to the evening element (EE) motif primarily found in the promoters of evening expressed genes. Using a genome-wide approach we have identified direct targets of CCA1 in plants grown in constant (LL) and driven conditions (LD). These CCA1 targets are enriched for a myriad of biological processes and stress responses. While many of these target genes are evening phased and contain the EE in their promoter regions, a significant subset is morning phased and lack an EE. Furthermore, several CCA1 targets do not cycle in either LL or LD or both. Expression analysis in CCA1 overexpressing plants confirms CCA1 regulation of analyzed targets. Our results emphasize an expanded role for the circadian clock in regulation of key pathways in Arabidopsis, and provide a comprehensive and solid resource for future functional studies. ChIP-Seq of CCA1-GFP plants under control of the CCA1 promoter in continuous light and diel conditions
Project description:In many organisms, the circadian clock is composed of functionally coupled morning and evening oscillators that regulate the bouts of dawn and dusk activity. In Arabidopsis, oscillator coupling relies on a core loop in which the evening oscillator component TOC1 was proposed to activate a subset of morning-expressed oscillator genes. Our systems-biological approach overturns the current view of the Arabidopsis circadian clock showing that TOC1 does not function as an activator but as a timely-controlled general repressor of morning and evening oscillator components. Repression occurs through rhythmic binding to the promoters of all oscillator genes, suggesting a previously unexpected direct connection between the morning and evening loops. Examination of TOC1 genome-wide binding using TOC1 Minigene (TMG) seedlings expressing the genomic fragment of TOC1 fused to the Yellow Fluorescent Protein in a toc1-2 mutant background (TMG-YFP/toc1-2 seedlings) grown under LD cycles (12h light:12h dark).
Project description:The plant circadian clock exerts a critical role in the regulation of multiple biological processes including responses to biotic and abiotic stresses. It is estimated that the clock regulates up to 80% of the transcriptome in Arabidopsis, thus understanding the molecular mechanisms that control this rhythmic transcriptome requires identification of the targets of each clock component. The Arabidopsis core clock is partially comprised of a transcriptional regulatory loop between the MYB domain containing transcription factors CIRCADIAN CLOCK ASSOCIATED1 (CCA1) and LATE ELONGATED HYPOCOTYL (LHY), and TIMING OF CAB EXPRESSION1 (TOC1). As a key component of the clock, CCA1 is able to initiate and set the phase of clock-controlled rhythms. CCA1 regulates the transcription of several genes by directly binding to the evening element (EE) motif primarily found in the promoters of evening expressed genes. Using a genome-wide approach we have identified direct targets of CCA1 in plants grown in constant (LL) and driven conditions (LD). These CCA1 targets are enriched for a myriad of biological processes and stress responses. While many of these target genes are evening phased and contain the EE in their promoter regions, a significant subset is morning phased and lack an EE. Furthermore, several CCA1 targets do not cycle in either LL or LD or both. Expression analysis in CCA1 overexpressing plants confirms CCA1 regulation of analyzed targets. Our results emphasize an expanded role for the circadian clock in regulation of key pathways in Arabidopsis, and provide a comprehensive and solid resource for future functional studies.
Project description:This study aim to understand how the long and short day flowering pathways are integrated and the mechanism of photoperiod perception in rice. Trascriptome at different time points under LD and SD conditions reveal that photoperiodism in rice is controlled by the evening complex. Mutants in LUX ARRYTHMO (LUX) and EARLY FLOWERING3 (ELF3) orthologs abolish flowering. We show that light causes a rapid and sustained degradation of ELF3-1, and this response is dependent on phyB. ChIP-seq of ELF3 and LUX reveal that EC controls both LD and SD flowering pathways by directly binding and suppressing the expression of key floral repressors, including PRR7 orthologs and Ghd7.
Project description:This study aim to understand how the long and short day flowering pathways are integrated and the mechanism of photoperiod perception in rice. Trascriptome at different time points under LD and SD conditions reveal that photoperiodism in rice is controlled by the evening complex. Mutants in LUX ARRYTHMO (LUX) and EARLY FLOWERING3 (ELF3) orthologs abolish flowering. We show that light causes a rapid and sustained degradation of ELF3-1, and this response is dependent on phyB. ChIP-seq of ELF3 and LUX reveal that EC controls both LD and SD flowering pathways by directly binding and suppressing the expression of key floral repressors, including PRR7 orthologs and Ghd7.
Project description:This model is from the article:
The clock gene circuit in Arabidopsis includes a repressilator with additional feedback loops
Pokhilko A, Fernández AP, Edwards KD, Southern MM, Halliday KJ, Millar AJ.
Mol Syst Biol.2012 Mar 6;8:574.
22395476,
Abstract:
Circadian clocks synchronise biological processes with the day/night cycle, using molecular mechanisms that include interlocked, transcriptional feedback loops. Recent experiments identified the evening complex (EC) as a repressor that can be essential for gene expression rhythms in plants. Integrating the EC components in this role significantly alters our mechanistic, mathematical model of the clock gene circuit. Negative autoregulation of the EC genes constitutes the clock's evening loop, replacing the hypothetical component Y. The EC explains our earlier conjecture that the morning gene PSEUDO-RESPONSE REGULATOR 9 was repressed by an evening gene, previously identified with TIMING OF CAB EXPRESSION1 (TOC1). Our computational analysis suggests that TOC1 is a repressor of the morning genes LATE ELONGATED HYPOCOTYL and CIRCADIAN CLOCK ASSOCIATED1 rather than an activator as first conceived. This removes the necessity for the unknown component X (or TOC1mod) from previous clock models. As well as matching timeseries and phase-response data, the model provides a new conceptual framework for the plant clock that includes a three-component repressilator circuit in its complex structure.
Project description:Arabidopsis thaliana is a well-established model system for the analysis of the basic physiological and metabolic pathways of plants. The presented model is a new semi-quantitative mathematical model of the metabolism of Arabidopsis thaliana. The Petri net formalism was used to express the complex reaction system in a mathematically unique manner. To verify the model for correctness and consistency concepts of network decomposition and network reduction such as transition invariants, common transition pairs, and invariant transition pairs were applied. Based on recent knowledge from literature, including the Calvin cycle, glycolysis and citric acid cycle, glyoxylate cycle, urea cycle, sucrose synthesis, and the starch metabolism, the core metabolism of Arabidopsis thaliana was formulated. Each reaction (transition) is experimentally proven. The complete Petri net model consists of 134 metabolites, represented by places, and 243 reactions, represented by transitions. Places and transitions are connected via 572 edges.
Project description:SAC3B, a central component of the mRNA export complex TREX-2, is required for prevention of epigenetic gene silencing in Arabidopsis