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Plant bio

Circadian rhythm in plants

QuestionAnswer
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: reub8n
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