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Discrete redox signaling pathways regulate photosynthetic light-harvesting and chloroplast gene transcription.

Allen JF, Santabarbara S, Allen CA, Puthiyaveetil S - PLoS ONE (2011)

Bottom Line: We asked whether CSK is also involved in regulation of absorbed light energy distribution by phosphorylation of light-harvesting complex II (LHC II).Chloroplast thylakoid membranes isolated from a CSK T-DNA insertion mutant and from wild-type Arabidopsis thaliana exhibit similar light- and redox-induced (32)P-labelling of LHC II and changes in 77 K chlorophyll fluorescence emission spectra, while room-temperature chlorophyll fluorescence emission transients from Arabidopsis leaves are perturbed by inactivation of CSK.The results indicate indirect, pleiotropic effects of reaction centre gene transcription on regulation of photosynthetic light-harvesting in vivo.

View Article: PubMed Central - PubMed

Affiliation: School of Biological and Chemical Sciences, Queen Mary University of London, London, United Kingdom. j.f.allen@qmul.ac.uk

ABSTRACT
In photosynthesis in chloroplasts, two related regulatory processes balance the actions of photosystems I and II. These processes are short-term, post-translational redistribution of light-harvesting capacity, and long-term adjustment of photosystem stoichiometry initiated by control of chloroplast DNA transcription. Both responses are initiated by changes in the redox state of the electron carrier, plastoquinone, which connects the two photosystems. Chloroplast Sensor Kinase (CSK) is a regulator of transcription of chloroplast genes for reaction centres of the two photosystems, and a sensor of plastoquinone redox state. We asked whether CSK is also involved in regulation of absorbed light energy distribution by phosphorylation of light-harvesting complex II (LHC II). Chloroplast thylakoid membranes isolated from a CSK T-DNA insertion mutant and from wild-type Arabidopsis thaliana exhibit similar light- and redox-induced (32)P-labelling of LHC II and changes in 77 K chlorophyll fluorescence emission spectra, while room-temperature chlorophyll fluorescence emission transients from Arabidopsis leaves are perturbed by inactivation of CSK. The results indicate indirect, pleiotropic effects of reaction centre gene transcription on regulation of photosynthetic light-harvesting in vivo. A single, direct redox signal is transmitted separately to discrete transcriptional and post-translational branches of an integrated cytoplasmic regulatory system.

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CSK mutants show normal LHC II phosphorylation.(a) Autoradiographs of Arabidopsis thylakoid phosphoproteins separated by SDS-PAGE. The positions of molecular weight markers are indicated on the left. Thylakoid samples from the wild-type (WT) and the CSK mutant are loaded in each lane and labelled accordingly at the top. The experimental conditions for each pair of samples are labelled at the bottom. (b) Coomassie-stained gel as protein loading control. The gel from which the autoradiograph was developed is stained with Coomassie brilliant blue to show that results presented in (a) results from 32P-labelling and not from unequal protein loading.
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pone-0026372-g003: CSK mutants show normal LHC II phosphorylation.(a) Autoradiographs of Arabidopsis thylakoid phosphoproteins separated by SDS-PAGE. The positions of molecular weight markers are indicated on the left. Thylakoid samples from the wild-type (WT) and the CSK mutant are loaded in each lane and labelled accordingly at the top. The experimental conditions for each pair of samples are labelled at the bottom. (b) Coomassie-stained gel as protein loading control. The gel from which the autoradiograph was developed is stained with Coomassie brilliant blue to show that results presented in (a) results from 32P-labelling and not from unequal protein loading.

Mentions: Phosphorylation of light harvesting complex II (LHC II) by the LHC II kinase induces state 2 transition, and its dephosphorylation by the phospho-LHC II phosphatase leads to state 1 transition [16], [25]. In order to further probe the role of CSK in state transitions, we carried out a thylakoid phosphorylation assay for the CSK mutant and the wild-type. Thylakoids were first isolated from white light grown plants, and incubated in light for 10 minutes in the presence of [γ-32P] ATP. The results of 32P-labelling experiments are shown in Figure 3. Incubation of thylakoids in white light induces the state 2 transition via phosphorylation of LHC II. Figure 3 shows equal levels of LHC II (protein band around 25 kDa) phosphorylation in both CSK mutant and wild type. In the light, the electron transport inhibitor 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) inhibits electron transport to plastoquinone and makes the plastoquinone pool oxidised. Oxidised plastoquinone promotes the state 1 transition, and LHC II remains in an unphosphorylated state. Thus, incubation of wild-type and CSK mutant thylakoids with DCMU in the presence of light abolishes 32P-labelling of LHC II (Figure 3).


Discrete redox signaling pathways regulate photosynthetic light-harvesting and chloroplast gene transcription.

Allen JF, Santabarbara S, Allen CA, Puthiyaveetil S - PLoS ONE (2011)

CSK mutants show normal LHC II phosphorylation.(a) Autoradiographs of Arabidopsis thylakoid phosphoproteins separated by SDS-PAGE. The positions of molecular weight markers are indicated on the left. Thylakoid samples from the wild-type (WT) and the CSK mutant are loaded in each lane and labelled accordingly at the top. The experimental conditions for each pair of samples are labelled at the bottom. (b) Coomassie-stained gel as protein loading control. The gel from which the autoradiograph was developed is stained with Coomassie brilliant blue to show that results presented in (a) results from 32P-labelling and not from unequal protein loading.
© Copyright Policy
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC3198397&req=5

pone-0026372-g003: CSK mutants show normal LHC II phosphorylation.(a) Autoradiographs of Arabidopsis thylakoid phosphoproteins separated by SDS-PAGE. The positions of molecular weight markers are indicated on the left. Thylakoid samples from the wild-type (WT) and the CSK mutant are loaded in each lane and labelled accordingly at the top. The experimental conditions for each pair of samples are labelled at the bottom. (b) Coomassie-stained gel as protein loading control. The gel from which the autoradiograph was developed is stained with Coomassie brilliant blue to show that results presented in (a) results from 32P-labelling and not from unequal protein loading.
Mentions: Phosphorylation of light harvesting complex II (LHC II) by the LHC II kinase induces state 2 transition, and its dephosphorylation by the phospho-LHC II phosphatase leads to state 1 transition [16], [25]. In order to further probe the role of CSK in state transitions, we carried out a thylakoid phosphorylation assay for the CSK mutant and the wild-type. Thylakoids were first isolated from white light grown plants, and incubated in light for 10 minutes in the presence of [γ-32P] ATP. The results of 32P-labelling experiments are shown in Figure 3. Incubation of thylakoids in white light induces the state 2 transition via phosphorylation of LHC II. Figure 3 shows equal levels of LHC II (protein band around 25 kDa) phosphorylation in both CSK mutant and wild type. In the light, the electron transport inhibitor 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) inhibits electron transport to plastoquinone and makes the plastoquinone pool oxidised. Oxidised plastoquinone promotes the state 1 transition, and LHC II remains in an unphosphorylated state. Thus, incubation of wild-type and CSK mutant thylakoids with DCMU in the presence of light abolishes 32P-labelling of LHC II (Figure 3).

Bottom Line: We asked whether CSK is also involved in regulation of absorbed light energy distribution by phosphorylation of light-harvesting complex II (LHC II).Chloroplast thylakoid membranes isolated from a CSK T-DNA insertion mutant and from wild-type Arabidopsis thaliana exhibit similar light- and redox-induced (32)P-labelling of LHC II and changes in 77 K chlorophyll fluorescence emission spectra, while room-temperature chlorophyll fluorescence emission transients from Arabidopsis leaves are perturbed by inactivation of CSK.The results indicate indirect, pleiotropic effects of reaction centre gene transcription on regulation of photosynthetic light-harvesting in vivo.

View Article: PubMed Central - PubMed

Affiliation: School of Biological and Chemical Sciences, Queen Mary University of London, London, United Kingdom. j.f.allen@qmul.ac.uk

ABSTRACT
In photosynthesis in chloroplasts, two related regulatory processes balance the actions of photosystems I and II. These processes are short-term, post-translational redistribution of light-harvesting capacity, and long-term adjustment of photosystem stoichiometry initiated by control of chloroplast DNA transcription. Both responses are initiated by changes in the redox state of the electron carrier, plastoquinone, which connects the two photosystems. Chloroplast Sensor Kinase (CSK) is a regulator of transcription of chloroplast genes for reaction centres of the two photosystems, and a sensor of plastoquinone redox state. We asked whether CSK is also involved in regulation of absorbed light energy distribution by phosphorylation of light-harvesting complex II (LHC II). Chloroplast thylakoid membranes isolated from a CSK T-DNA insertion mutant and from wild-type Arabidopsis thaliana exhibit similar light- and redox-induced (32)P-labelling of LHC II and changes in 77 K chlorophyll fluorescence emission spectra, while room-temperature chlorophyll fluorescence emission transients from Arabidopsis leaves are perturbed by inactivation of CSK. The results indicate indirect, pleiotropic effects of reaction centre gene transcription on regulation of photosynthetic light-harvesting in vivo. A single, direct redox signal is transmitted separately to discrete transcriptional and post-translational branches of an integrated cytoplasmic regulatory system.

Show MeSH
Related in: MedlinePlus