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Dawn and Dusk Set States of the Circadian Oscillator in Sprouting Barley (Hordeum vulgare) Seedlings.

Deng W, Clausen J, Boden S, Oliver SN, Casao MC, Ford B, Anderssen RS, Trevaskis B - PLoS ONE (2015)

Bottom Line: Oscillations of clock gene transcript levels do not occur in barley seedlings grown in darkness or constant light but were observed with day-night cycles.A barley EARLY FLOWERING3 mutant, which exhibits rapid photoperiod-insensitive flowering behaviour, does not establish clock rhythms in response to a single photoperiod.The data presented show that dawn and dusk cues are important signals for setting the state of the circadian oscillator during early development of barley and that the circadian oscillator of barley exhibits photoperiod-dependent oscillation states.

View Article: PubMed Central - PubMed

Affiliation: CSIRO, Agriculture, GPO Box 1600, Canberra, ACT, 2601, Australia.

ABSTRACT
The plant circadian clock is an internal timekeeper that coordinates biological processes with daily changes in the external environment. The transcript levels of clock genes, which oscillate to control circadian outputs, were examined during early seedling development in barley (Hordeum vulgare), a model for temperate cereal crops. Oscillations of clock gene transcript levels do not occur in barley seedlings grown in darkness or constant light but were observed with day-night cycles. A dark-to-light transition influenced transcript levels of some clock genes but triggered only weak oscillations of gene expression, whereas a light-to-dark transition triggered robust oscillations. Single light pulses of 6, 12 or 18 hours induced robust oscillations. The light-to-dark transition was the primary determinant of the timing of subsequent peaks of clock gene expression. After the light-to-dark transition the timing of peak transcript levels of clock gene also varied depending on the length of the preceding light pulse. Thus, a single photoperiod can trigger initiation of photoperiod-dependent circadian rhythms in barley seedlings. Photoperiod-specific rhythms of clock gene expression were observed in two week old barley plants. Changing the timing of dusk altered clock gene expression patterns within a single day, showing that alteration of circadian oscillator behaviour is amongst the most rapid molecular responses to changing photoperiod in barley. A barley EARLY FLOWERING3 mutant, which exhibits rapid photoperiod-insensitive flowering behaviour, does not establish clock rhythms in response to a single photoperiod. The data presented show that dawn and dusk cues are important signals for setting the state of the circadian oscillator during early development of barley and that the circadian oscillator of barley exhibits photoperiod-dependent oscillation states.

No MeSH data available.


Related in: MedlinePlus

Expression of clock genes assayed in barley seedlings grown in different light regimes.Clock gene expression assayed by quantitative reverse transcriptase PCR (qRT-PCR) in 5 day old barley seedlings (cv. Sonja) germinated and grown in constant temperature conditions (20°C) with (A) 12 hour day-night cycles with light from hours 0 to 12, (B) constant darkness or (C) constant light. Average expression in RNA extracted from individual seedlings (3 biological repeats) is shown relative to ACTIN (Rel. exp.), error bars show standard error. Horizontal axis labels indicate the time (hours) relative to when the first sample was harvested. Samples were harvested directly from the described conditions (i.e. without free running conditions for the day-night cycle samples).
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pone.0129781.g001: Expression of clock genes assayed in barley seedlings grown in different light regimes.Clock gene expression assayed by quantitative reverse transcriptase PCR (qRT-PCR) in 5 day old barley seedlings (cv. Sonja) germinated and grown in constant temperature conditions (20°C) with (A) 12 hour day-night cycles with light from hours 0 to 12, (B) constant darkness or (C) constant light. Average expression in RNA extracted from individual seedlings (3 biological repeats) is shown relative to ACTIN (Rel. exp.), error bars show standard error. Horizontal axis labels indicate the time (hours) relative to when the first sample was harvested. Samples were harvested directly from the described conditions (i.e. without free running conditions for the day-night cycle samples).

Mentions: Clock gene transcript levels were first assayed in 5 day old barley seedlings grown in 12 hour day-night cycles. Rhythmic oscillations of transcript levels were observed for several clock genes including HvCCA1, HvTOC1, HvGI, HvPRR73, HvPRR59 and HvPRR95 (Fig 1A, S1 Fig), similar to previous reports (e.g. [24]). A number of clock-regulated genes also showed rhythmic expression, consistent with the observed clock gene oscillations; PHOTOPERIOD1 (HvPPD1), VERNALIZATION2 (HvVRN2), a barley CO orthologue (HvCO1), a glycine-rich protein (HvGRP7, also known as CIRCADIAN CLOCK REGULATED2, CCR2) and chlorophyll AB binding proteins (HvCAB1, HvLHCII) (S2 Fig).


Dawn and Dusk Set States of the Circadian Oscillator in Sprouting Barley (Hordeum vulgare) Seedlings.

Deng W, Clausen J, Boden S, Oliver SN, Casao MC, Ford B, Anderssen RS, Trevaskis B - PLoS ONE (2015)

Expression of clock genes assayed in barley seedlings grown in different light regimes.Clock gene expression assayed by quantitative reverse transcriptase PCR (qRT-PCR) in 5 day old barley seedlings (cv. Sonja) germinated and grown in constant temperature conditions (20°C) with (A) 12 hour day-night cycles with light from hours 0 to 12, (B) constant darkness or (C) constant light. Average expression in RNA extracted from individual seedlings (3 biological repeats) is shown relative to ACTIN (Rel. exp.), error bars show standard error. Horizontal axis labels indicate the time (hours) relative to when the first sample was harvested. Samples were harvested directly from the described conditions (i.e. without free running conditions for the day-night cycle samples).
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4465908&req=5

pone.0129781.g001: Expression of clock genes assayed in barley seedlings grown in different light regimes.Clock gene expression assayed by quantitative reverse transcriptase PCR (qRT-PCR) in 5 day old barley seedlings (cv. Sonja) germinated and grown in constant temperature conditions (20°C) with (A) 12 hour day-night cycles with light from hours 0 to 12, (B) constant darkness or (C) constant light. Average expression in RNA extracted from individual seedlings (3 biological repeats) is shown relative to ACTIN (Rel. exp.), error bars show standard error. Horizontal axis labels indicate the time (hours) relative to when the first sample was harvested. Samples were harvested directly from the described conditions (i.e. without free running conditions for the day-night cycle samples).
Mentions: Clock gene transcript levels were first assayed in 5 day old barley seedlings grown in 12 hour day-night cycles. Rhythmic oscillations of transcript levels were observed for several clock genes including HvCCA1, HvTOC1, HvGI, HvPRR73, HvPRR59 and HvPRR95 (Fig 1A, S1 Fig), similar to previous reports (e.g. [24]). A number of clock-regulated genes also showed rhythmic expression, consistent with the observed clock gene oscillations; PHOTOPERIOD1 (HvPPD1), VERNALIZATION2 (HvVRN2), a barley CO orthologue (HvCO1), a glycine-rich protein (HvGRP7, also known as CIRCADIAN CLOCK REGULATED2, CCR2) and chlorophyll AB binding proteins (HvCAB1, HvLHCII) (S2 Fig).

Bottom Line: Oscillations of clock gene transcript levels do not occur in barley seedlings grown in darkness or constant light but were observed with day-night cycles.A barley EARLY FLOWERING3 mutant, which exhibits rapid photoperiod-insensitive flowering behaviour, does not establish clock rhythms in response to a single photoperiod.The data presented show that dawn and dusk cues are important signals for setting the state of the circadian oscillator during early development of barley and that the circadian oscillator of barley exhibits photoperiod-dependent oscillation states.

View Article: PubMed Central - PubMed

Affiliation: CSIRO, Agriculture, GPO Box 1600, Canberra, ACT, 2601, Australia.

ABSTRACT
The plant circadian clock is an internal timekeeper that coordinates biological processes with daily changes in the external environment. The transcript levels of clock genes, which oscillate to control circadian outputs, were examined during early seedling development in barley (Hordeum vulgare), a model for temperate cereal crops. Oscillations of clock gene transcript levels do not occur in barley seedlings grown in darkness or constant light but were observed with day-night cycles. A dark-to-light transition influenced transcript levels of some clock genes but triggered only weak oscillations of gene expression, whereas a light-to-dark transition triggered robust oscillations. Single light pulses of 6, 12 or 18 hours induced robust oscillations. The light-to-dark transition was the primary determinant of the timing of subsequent peaks of clock gene expression. After the light-to-dark transition the timing of peak transcript levels of clock gene also varied depending on the length of the preceding light pulse. Thus, a single photoperiod can trigger initiation of photoperiod-dependent circadian rhythms in barley seedlings. Photoperiod-specific rhythms of clock gene expression were observed in two week old barley plants. Changing the timing of dusk altered clock gene expression patterns within a single day, showing that alteration of circadian oscillator behaviour is amongst the most rapid molecular responses to changing photoperiod in barley. A barley EARLY FLOWERING3 mutant, which exhibits rapid photoperiod-insensitive flowering behaviour, does not establish clock rhythms in response to a single photoperiod. The data presented show that dawn and dusk cues are important signals for setting the state of the circadian oscillator during early development of barley and that the circadian oscillator of barley exhibits photoperiod-dependent oscillation states.

No MeSH data available.


Related in: MedlinePlus