ABSTRACT
Recent studies have demonstrated the importance of temporal regulation of pathogen defense by the circadian clock. However, our understanding of the molecular basis underlying this role of the circadian clock is still in its infancy. We report here the mechanism by which the Arabidopsis master clock protein CCA1 regulates an output target gene GRP7 for its circadian expression and function in pathogen defense. Our data firmly establish that CCA1 physically associates with the GRP7 promoter via the predicted CCA1-binding motif, evening element (EE). A site-directed mutagenesis study showed that while individual EE motifs differentially contribute to robust circadian expression of GRP7, abolishing all four EE motifs in the proximal GRP7 promoter disrupts rhythmicity of GRP7 expression and results in misalignment of defense signaling mediated by GRP7 and altered pathogen responses. This study provides a mechanistic link of the circadian regulation of an output gene to its biological function in pathogen defense, underscoring the importance of temporal control of plant innate immunity.
Subject(s)
Arabidopsis Proteins , Arabidopsis , Circadian Clocks , Arabidopsis Proteins/genetics , Arabidopsis Proteins/metabolism , Circadian Clocks/genetics , CLOCK Proteins/genetics , CLOCK Proteins/metabolism , Arabidopsis/metabolism , Glycine/genetics , Glycine/metabolism , RNA-Binding Proteins/genetics , RNA-Binding Proteins/metabolism , Immunity, Innate/genetics , Gene Expression Regulation, Plant , Circadian Rhythm/geneticsABSTRACT
The circadian clock is known to regulate plant innate immunity but the underlying mechanism of this regulation remains largely unclear. We show here that mutations in the core clock component LUX ARRHYTHMO (LUX) disrupt circadian regulation of stomata under free running and Pseudomonas syringae challenge conditions as well as defense signaling mediated by SA and JA, leading to compromised disease resistance. RNA-seq analysis reveals that both clock- and defense-related genes are regulated by LUX. LUX binds to clock gene promoters that have not been shown before, expanding the clock gene networks that require LUX function. LUX also binds to the promoters of EDS1 and JAZ5, likely acting through these genes to affect SA- and JA-signaling. We further show that JA signaling reciprocally affects clock activity. Thus, our data support crosstalk between the circadian clock and plant innate immunity and imply an important role of LUX in this process.
Subject(s)
Arabidopsis/genetics , Circadian Clocks/genetics , Plant Immunity/genetics , Arabidopsis/microbiology , Circadian Clocks/physiology , Disease Resistance/genetics , Gene Expression Regulation, Plant , Mutation , Plant Diseases/immunology , Plant Diseases/microbiology , Plant Stomata/physiology , Pseudomonas syringae/physiology , Sequence Analysis, RNAABSTRACT
A series of a rigid meso-meso directly linked chlorin-chlorin, chlorin-bacteriochlorin, and bacteriochlorin-bacteriochlorin dyads, including free bases as well as Zn(II), Pd(II), and Cu(II) complexes, has been synthesized, and their absorption, emission, singlet oxygen (1O2) photosensitization, and electronic properties have been examined. Marked bathochromic shifts of the long-wavelength Q y absorption band and increase in fluorescence quantum yields in dyads, in comparison to the corresponding monomers, are observed. Nonsymmetrical dyads (except bacteriochlorin-bacteriochlorin) show two distinctive Q y bands, corresponding to the absorption of each dyad component. A nearly quantitative S1-S1 energy transfer between hydroporphyrins in dyads, leading to an almost exclusive emission of hydroporphyrin with a lower S1 energy, has been determined. Several symmetrical and all nonsymmetrical dyads exhibit a significant reduction in fluorescence quantum yields in solvents of high dielectric constants; this is attributed to the photoinduced electron transfer. The complexation of one macrocycle by Cu(II) or Pd(II) enhances intersystem crossing in the adjacent, free base dyad component, which is manifested by a significant reduction in fluorescence and increase in quantum yield of 1O2 photosensitization.
Subject(s)
Metalloporphyrins/chemical synthesis , Metalloporphyrins/radiation effects , Coordination Complexes/chemical synthesis , Coordination Complexes/chemistry , Coordination Complexes/radiation effects , Copper/chemistry , Energy Transfer , Fluorescence , Metalloporphyrins/chemistry , Models, Chemical , Palladium/chemistry , Photosensitizing Agents/chemical synthesis , Photosensitizing Agents/chemistry , Photosensitizing Agents/radiation effects , Quantum Theory , Singlet Oxygen/chemistry , Zinc/chemistryABSTRACT
Symmetrical, near-infrared absorbing bacteriochlorin dyads exhibit gradual reduction of their fluorescence (intensity and lifetime) and reactive oxygen species photosensitization efficiency (ROS) with increasing solvent dielectric constant ε. For the directly linked dyad, significant reduction is observed even in solvents of moderate ε, while for the dyad containing a 1,4-phenylene linker, reduction is more parallel to an increase in solvent ε. Bacteriochlorin dyads are promising candidates for development of environmentally responsive fluorophores and ROS sensitizers.
