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Plant bio
Circadian rhythm in plants
| Question | Answer |
|---|---|
| Circadian clocks regulate plant cells by controlling gene expression | Some circadian clock proteins are transcription factors that regulate sets of genes with a circadian rhythm |
| Transcriptome analysis reveals extent of circadian regulation | - first sample RNA over 24hr/48hr period - analyze transcripts from all genes using microarray or RNA sequencing methods - study found 6% of transcripts have circadian rhythms - many photosynthesis have circadian rhythms |
| Specific gene promoter sequences may underlie specific circadian phases of transcription | - cis elements occur with high frequency in promoters of transcript sets with circadian phases - indicates the clock regulates different subsets of genes with a different phases |
| Circadian clock and plant metabolism | Almost all metabolic pathways include at least one enzyme that is under circadian transcriptional control |
| Many metabolic pathways have physiologically appropriate phases of maximal transcript abundance | - chlorophyll biosynthesis genes peak just before dawn to anticipate light availability - starch catabolism genes peak around dusk |
| Circadian clock mutants have altered metabolite levels in light/dark cycles | |
| Carbohydrate degradation at night is controlled temporally | The rate of starch degradation is related to the length of the night, so that the plant only exhausts starch reserves just before the end of the night |
| The chloroplast has circadian rhythms of gene expression that are controlled by the nucleus | |
| The oscillator, environmental signalling and metabolism form an integrated network | |
| Circadian gating | - The regulation of other cell signaling pathways by the circadian clock is known as circadian gating - It is a fundamental way that circadian clocks regulate plant cells |
| During gating, the clock acts as a valve on the response of the plant to the environment, so the same environmental cue causes a different strength response depending on the time of day | |
| At some times of day the gate is open and the signal passes through. At other times of day the gate is closed and the signal cannot pass through | |
| Circadian gating acts upon circadian entrainment and environmental signalling pathways | 1.The circadian clock gates the light and temperature signals that entrain the circadian clock 2.The circadian clock gates signalling pathways that regulate the responses of plants to the environment |
| 1. Circadian gating of light input for circadian entrainment | If the circadian clock responded identically to light at every time of day, it would be reset to dawn continuously and be unable to provide a measure of time |
| The clock regulates its own sensitivity to light, so the way it responds to light depends on the time of day | |
| 2. Circadian gating of environmental response pathways | |
| Case study: The role of Ppd-H1 in photoperiodic responses of barley | Barley (Hordeum vulgare): - Long-day plant, i.e., it requires day lengths in excess of a critical minimum to flower. - There are also varieties that are insensitive to day length |
| Ppd-H1 is a homologue of the Arabidopsis PRR7 oscillator gene | |
| Winter barley (Ppd-H1) is photoperiod sensitive and flowers in early spring | |
| Spring barley (ppd-H1) is photoperiod insensitive and flowers late |
Created by:
rose.coo
Popular Ecology sets