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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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Clock activity of plants misexpressing CCA1 and/or LHY is disrupted in LD.Eight-day-old seedlings of Col-0, cca1-1, lhy-20, cca1-1lhy-20, and CCA1ox expressing ProCCA1:LUC reporter were grown from germination in 12 hr light/12 hr dark cycles at 22°C. Luciferase activity was recorded with a Packard TopCount luminometer in LD at 22°C. (A) Mean circadian traces for ProCCA1:LUC activity. (B) Summary of phase value for ProCCA1:LUC in each genotype. Standard error of the mean (SEM) (n = 12–24) was used for (A) and (B). Letters indicate significant difference among the samples (P<0.05; Student's t-test).
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ppat-1003370-g001: Clock activity of plants misexpressing CCA1 and/or LHY is disrupted in LD.Eight-day-old seedlings of Col-0, cca1-1, lhy-20, cca1-1lhy-20, and CCA1ox expressing ProCCA1:LUC reporter were grown from germination in 12 hr light/12 hr dark cycles at 22°C. Luciferase activity was recorded with a Packard TopCount luminometer in LD at 22°C. (A) Mean circadian traces for ProCCA1:LUC activity. (B) Summary of phase value for ProCCA1:LUC in each genotype. Standard error of the mean (SEM) (n = 12–24) was used for (A) and (B). Letters indicate significant difference among the samples (P<0.05; Student's t-test).

Mentions: To evaluate defense roles of CCA1 and LHY, we constructed the cca1-1lhy-20 mutant via a genetic cross in a Col-0 background that also contains the LUCIFERASE reporter gene driven by the CCA1 promoter (ProCCA1:LUC). The single loss of function mutants, cca1-1 and lhy-20, have shortened circadian periods of ProCCA1:LUC expression in constant light (LL) [11]. In LL, we confirmed that cca1-1lhy-20 had a much-shortened period (19.9±0.11 hr), compared with wild type (wt) Col-0 (24.4±0.09 hr) (Figure S1A and [19]). Although experiments in LL are important for establishing the involvement of the circadian clock in specific phenotypes, such experimental conditions can also be limiting. In entraining conditions (e.g., a 12 hr L/12 hr D cycle; LD), the altered period of clock mutants like cca1-1 and lhy-20 is not seen due to the entraining cycle, which imposes a 24 hr period (Figure 1). The clock remains important in such LD conditions, though, because the clock determines the phase of specific events with respect to as dawn and dusk. Mutants with altered period in LL typically exhibit altered phase in LD, with short period mutants exhibiting a leading (early) phase and long period mutants exhibiting a lagging (late) phase [32]. Moreover, interactions between the endogenous circadian clock and external LD cycles can results in phase differences, sometimes dramatic, when measured in LD versus LL. For example, the phase of maximal hypocotyl elongation during early seedling growth was shifted 8–12 hours between LD and LL conditions [33], [34]. In their natural environment, plants do not usually encounter LL. Therefore in evaluating the role of the circadian clock on plant defense against pathogens, it is critically important to study plant-pathogen interactions in LD and to consider the potential influence of the circadian clock on the phases of rhythmic events that might influence the plant response to pathogen challenge.


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)

Clock activity of plants misexpressing CCA1 and/or LHY is disrupted in LD.Eight-day-old seedlings of Col-0, cca1-1, lhy-20, cca1-1lhy-20, and CCA1ox expressing ProCCA1:LUC reporter were grown from germination in 12 hr light/12 hr dark cycles at 22°C. Luciferase activity was recorded with a Packard TopCount luminometer in LD at 22°C. (A) Mean circadian traces for ProCCA1:LUC activity. (B) Summary of phase value for ProCCA1:LUC in each genotype. Standard error of the mean (SEM) (n = 12–24) was used for (A) and (B). Letters indicate significant difference among the samples (P<0.05; Student's t-test).
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Related In: Results  -  Collection

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ppat-1003370-g001: Clock activity of plants misexpressing CCA1 and/or LHY is disrupted in LD.Eight-day-old seedlings of Col-0, cca1-1, lhy-20, cca1-1lhy-20, and CCA1ox expressing ProCCA1:LUC reporter were grown from germination in 12 hr light/12 hr dark cycles at 22°C. Luciferase activity was recorded with a Packard TopCount luminometer in LD at 22°C. (A) Mean circadian traces for ProCCA1:LUC activity. (B) Summary of phase value for ProCCA1:LUC in each genotype. Standard error of the mean (SEM) (n = 12–24) was used for (A) and (B). Letters indicate significant difference among the samples (P<0.05; Student's t-test).
Mentions: To evaluate defense roles of CCA1 and LHY, we constructed the cca1-1lhy-20 mutant via a genetic cross in a Col-0 background that also contains the LUCIFERASE reporter gene driven by the CCA1 promoter (ProCCA1:LUC). The single loss of function mutants, cca1-1 and lhy-20, have shortened circadian periods of ProCCA1:LUC expression in constant light (LL) [11]. In LL, we confirmed that cca1-1lhy-20 had a much-shortened period (19.9±0.11 hr), compared with wild type (wt) Col-0 (24.4±0.09 hr) (Figure S1A and [19]). Although experiments in LL are important for establishing the involvement of the circadian clock in specific phenotypes, such experimental conditions can also be limiting. In entraining conditions (e.g., a 12 hr L/12 hr D cycle; LD), the altered period of clock mutants like cca1-1 and lhy-20 is not seen due to the entraining cycle, which imposes a 24 hr period (Figure 1). The clock remains important in such LD conditions, though, because the clock determines the phase of specific events with respect to as dawn and dusk. Mutants with altered period in LL typically exhibit altered phase in LD, with short period mutants exhibiting a leading (early) phase and long period mutants exhibiting a lagging (late) phase [32]. Moreover, interactions between the endogenous circadian clock and external LD cycles can results in phase differences, sometimes dramatic, when measured in LD versus LL. For example, the phase of maximal hypocotyl elongation during early seedling growth was shifted 8–12 hours between LD and LL conditions [33], [34]. In their natural environment, plants do not usually encounter LL. Therefore in evaluating the role of the circadian clock on plant defense against pathogens, it is critically important to study plant-pathogen interactions in LD and to consider the potential influence of the circadian clock on the phases of rhythmic events that might influence the plant response to pathogen challenge.

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