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Crosstalk between the circadian clock and innate immunity in Arabidopsis.

Zhang C, Xie Q, Anderson RG, Ng G, Seitz NC, Peterson T, McClung CR, McDowell JM, Kong D, Kwak JM, Lu H - PLoS Pathog. (2013)

Bottom Line: Recently, the circadian clock has been shown to affect plant responses to biotic cues.Furthermore, we found defense activation by P. syringae infection and treatment with the elicitor flg22 can feedback-regulate clock activity.Together this data strongly supports a direct role of the circadian clock in defense control and reveal for the first time crosstalk between the circadian clock and plant innate immunity.

View Article: PubMed Central - PubMed

Affiliation: Department of Biological Sciences, University of Maryland Baltimore County, Baltimore, Maryland, United States of America.

ABSTRACT
The circadian clock integrates temporal information with environmental cues in regulating plant development and physiology. Recently, the circadian clock has been shown to affect plant responses to biotic cues. To further examine this role of the circadian clock, we tested disease resistance in mutants disrupted in CCA1 and LHY, which act synergistically to regulate clock activity. We found that cca1 and lhy mutants also synergistically affect basal and resistance gene-mediated defense against Pseudomonas syringae and Hyaloperonospora arabidopsidis. Disrupting the circadian clock caused by overexpression of CCA1 or LHY also resulted in severe susceptibility to P. syringae. We identified a downstream target of CCA1 and LHY, GRP7, a key constituent of a slave oscillator regulated by the circadian clock and previously shown to influence plant defense and stomatal activity. We show that the defense role of CCA1 and LHY against P. syringae is at least partially through circadian control of stomatal aperture but is independent of defense mediated by salicylic acid. Furthermore, we found defense activation by P. syringae infection and treatment with the elicitor flg22 can feedback-regulate clock activity. Together this data strongly supports a direct role of the circadian clock in defense control and reveal for the first time crosstalk between the circadian clock and plant innate immunity.

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The clock period is shortened by treatment with flg22 but not with BTH.(A) Mean circadian period of the ProCCA1:LUC reporter. Eight-day-old Col-0 seedlings expressing the ProCCA1:LUC reporter were grown from germination in 12 hr light/12 hr dark cycles at 22°C. At ZT7, eight-day-old seedlings were treated with flg22 (1 µM or 10 µM) or BTH (10 µM or 300 µM) and transferred to 96-well plates containing 200 µl of MS media and 30 µl of a 2.5 mM D-luciferin solution. Luciferase activity was recorded with a Packard TopCount luminometer in LL at 22°C. (B) Cotyledon movement assay with acd6-1. Eight-day-old acd6-1 seedlings grown in a 12 hr light/121 hr dark cycle at 22°C were transferred to 24-well cloning plates and recorded in LL at 22°C for cotyledon movement. SEM (n = 12–24) was used for (A) and (B). These experiments were repeated twice with similar results.
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ppat-1003370-g011: The clock period is shortened by treatment with flg22 but not with BTH.(A) Mean circadian period of the ProCCA1:LUC reporter. Eight-day-old Col-0 seedlings expressing the ProCCA1:LUC reporter were grown from germination in 12 hr light/12 hr dark cycles at 22°C. At ZT7, eight-day-old seedlings were treated with flg22 (1 µM or 10 µM) or BTH (10 µM or 300 µM) and transferred to 96-well plates containing 200 µl of MS media and 30 µl of a 2.5 mM D-luciferin solution. Luciferase activity was recorded with a Packard TopCount luminometer in LL at 22°C. (B) Cotyledon movement assay with acd6-1. Eight-day-old acd6-1 seedlings grown in a 12 hr light/121 hr dark cycle at 22°C were transferred to 24-well cloning plates and recorded in LL at 22°C for cotyledon movement. SEM (n = 12–24) was used for (A) and (B). These experiments were repeated twice with similar results.

Mentions: To further investigate which defense signaling pathway(s) are involved in the feedback-regulation of clock activity, we treated Col-0/ProCCA1:LUC seedlings with flg22 or benzo (1,2,3) thiadiazole-7-carbothioic acid (BTH). Flg22 is a 22-aa synthetic peptide from the conserved region of flagellin proteins of P. syringae and elicits plant basal defense in a wide variety of plant species [4], [57]. BTH is an agonist of SA that efficiently activates SA signaling [58]. We found that flg22 at both doses (1 µM and 10 µM) significantly shortened the period of CCA1 expression. However, BTH treatment (10 µM and 300 µM) did not change CCA1 promoter activity (Figure 11A and Table S3). To further test if SA could affect clock activity, we used a cotyledon movement assay [59] to gauge clock activity in the acd6-1 mutant, which constitutively accumulates high levels of SA [52], [53]. We found that acd6-1 showed similar period, phase, and amplitude of the rhythm for cotyledon movement to Col-0 (Figure 11B and S8). Taken together, these data indicate that activation of flg22-triggered basal defense but not SA signaling can feedback to regulate clock activity.


Crosstalk between the circadian clock and innate immunity in Arabidopsis.

Zhang C, Xie Q, Anderson RG, Ng G, Seitz NC, Peterson T, McClung CR, McDowell JM, Kong D, Kwak JM, Lu H - PLoS Pathog. (2013)

The clock period is shortened by treatment with flg22 but not with BTH.(A) Mean circadian period of the ProCCA1:LUC reporter. Eight-day-old Col-0 seedlings expressing the ProCCA1:LUC reporter were grown from germination in 12 hr light/12 hr dark cycles at 22°C. At ZT7, eight-day-old seedlings were treated with flg22 (1 µM or 10 µM) or BTH (10 µM or 300 µM) and transferred to 96-well plates containing 200 µl of MS media and 30 µl of a 2.5 mM D-luciferin solution. Luciferase activity was recorded with a Packard TopCount luminometer in LL at 22°C. (B) Cotyledon movement assay with acd6-1. Eight-day-old acd6-1 seedlings grown in a 12 hr light/121 hr dark cycle at 22°C were transferred to 24-well cloning plates and recorded in LL at 22°C for cotyledon movement. SEM (n = 12–24) was used for (A) and (B). These experiments were repeated twice with similar results.
© Copyright Policy
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC3675028&req=5

ppat-1003370-g011: The clock period is shortened by treatment with flg22 but not with BTH.(A) Mean circadian period of the ProCCA1:LUC reporter. Eight-day-old Col-0 seedlings expressing the ProCCA1:LUC reporter were grown from germination in 12 hr light/12 hr dark cycles at 22°C. At ZT7, eight-day-old seedlings were treated with flg22 (1 µM or 10 µM) or BTH (10 µM or 300 µM) and transferred to 96-well plates containing 200 µl of MS media and 30 µl of a 2.5 mM D-luciferin solution. Luciferase activity was recorded with a Packard TopCount luminometer in LL at 22°C. (B) Cotyledon movement assay with acd6-1. Eight-day-old acd6-1 seedlings grown in a 12 hr light/121 hr dark cycle at 22°C were transferred to 24-well cloning plates and recorded in LL at 22°C for cotyledon movement. SEM (n = 12–24) was used for (A) and (B). These experiments were repeated twice with similar results.
Mentions: To further investigate which defense signaling pathway(s) are involved in the feedback-regulation of clock activity, we treated Col-0/ProCCA1:LUC seedlings with flg22 or benzo (1,2,3) thiadiazole-7-carbothioic acid (BTH). Flg22 is a 22-aa synthetic peptide from the conserved region of flagellin proteins of P. syringae and elicits plant basal defense in a wide variety of plant species [4], [57]. BTH is an agonist of SA that efficiently activates SA signaling [58]. We found that flg22 at both doses (1 µM and 10 µM) significantly shortened the period of CCA1 expression. However, BTH treatment (10 µM and 300 µM) did not change CCA1 promoter activity (Figure 11A and Table S3). To further test if SA could affect clock activity, we used a cotyledon movement assay [59] to gauge clock activity in the acd6-1 mutant, which constitutively accumulates high levels of SA [52], [53]. We found that acd6-1 showed similar period, phase, and amplitude of the rhythm for cotyledon movement to Col-0 (Figure 11B and S8). Taken together, these data indicate that activation of flg22-triggered basal defense but not SA signaling can feedback to regulate clock activity.

Bottom Line: Recently, the circadian clock has been shown to affect plant responses to biotic cues.Furthermore, we found defense activation by P. syringae infection and treatment with the elicitor flg22 can feedback-regulate clock activity.Together this data strongly supports a direct role of the circadian clock in defense control and reveal for the first time crosstalk between the circadian clock and plant innate immunity.

View Article: PubMed Central - PubMed

Affiliation: Department of Biological Sciences, University of Maryland Baltimore County, Baltimore, Maryland, United States of America.

ABSTRACT
The circadian clock integrates temporal information with environmental cues in regulating plant development and physiology. Recently, the circadian clock has been shown to affect plant responses to biotic cues. To further examine this role of the circadian clock, we tested disease resistance in mutants disrupted in CCA1 and LHY, which act synergistically to regulate clock activity. We found that cca1 and lhy mutants also synergistically affect basal and resistance gene-mediated defense against Pseudomonas syringae and Hyaloperonospora arabidopsidis. Disrupting the circadian clock caused by overexpression of CCA1 or LHY also resulted in severe susceptibility to P. syringae. We identified a downstream target of CCA1 and LHY, GRP7, a key constituent of a slave oscillator regulated by the circadian clock and previously shown to influence plant defense and stomatal activity. We show that the defense role of CCA1 and LHY against P. syringae is at least partially through circadian control of stomatal aperture but is independent of defense mediated by salicylic acid. Furthermore, we found defense activation by P. syringae infection and treatment with the elicitor flg22 can feedback-regulate clock activity. Together this data strongly supports a direct role of the circadian clock in defense control and reveal for the first time crosstalk between the circadian clock and plant innate immunity.

Show MeSH
Related in: MedlinePlus