Dataset Information

Downregulation of TAP38/PPH1 enables LHCII hyperphosphorylation in Arabidopsis mutant lacking LHCII docking site in PSI.

ABSTRACT: Redox-regulated reversible phosphorylation of the light-harvesting complex II (LHCII) controls the excitation energy distribution between photosystem (PS) II and PSI. The PsaL and PsaH subunits of PSI enable the association of pLHCII to PSI. Here, we show that the failure of the psal mutant to dock pLHCII to PSI induces excessive phosphorylation of LHCII, primarily due to a marked downregulation of the TAP38/PPH1 phosphatase occurring at post-transcriptional level. TAP38/PPH1 is shown to be associated with megacomplex that contains both photosystems in a light- and LHCII-PSII core-phosphorylation-dependent manner. It is suggested that proper megacomplex-related association of TAP38/PPH1 protects it against degradation.

SUBMITTER: Rantala M

PROVIDER: S-EPMC5021135 | biostudies-literature | 2016 Mar

REPOSITORIES: biostudies-literature

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Downregulation of TAP38/PPH1 enables LHCII hyperphosphorylation in Arabidopsis mutant lacking LHCII docking site in PSI.

Rantala Marjaana M Lehtimäki Nina N Aro Eva-Mari EM Suorsa Marjaana M

FEBS letters 20160308 6

Redox-regulated reversible phosphorylation of the light-harvesting complex II (LHCII) controls the excitation energy distribution between photosystem (PS) II and PSI. The PsaL and PsaH subunits of PSI enable the association of pLHCII to PSI. Here, we show that the failure of the psal mutant to dock pLHCII to PSI induces excessive phosphorylation of LHCII, primarily due to a marked downregulation of the TAP38/PPH1 phosphatase occurring at post-transcriptional level. TAP38/PPH1 is shown to be asso ...[more]

PMID: 26926011

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Project description:BackgroundThe light-harvesting antennae of photosystem (PS) I and PSII are pigment-protein complexes responsible of the initial steps of sunlight conversion into chemical energy. In natural environments plants are constantly confronted with the variability of the photosynthetically active light spectrum. PSII and PSI operate in series but have different optimal excitation wavelengths. The prompt adjustment of light absorption by photosystems is thus crucial to ensure efficient electron flow needed to sustain downstream carbon fixing reactions. Fast structural rearrangements equilibrate the partition of excitation pressure between PSII and PSI following the enrichment in the red (PSII-favoring) or far-red (PSI-favoring) spectra. Redox imbalances trigger state transitions (ST), a photoacclimation mechanism which involves the reversible phosphorylation/dephosphorylation of light harvesting complex II (LHCII) proteins by the antagonistic activities of the State Transition 7 (STN7) kinase/TAP38 phosphatase enzyme pair. During ST, a mobile PSII antenna pool associates with PSI increasing its absorption cross section. LHCII consists of assorted trimeric assemblies of Lhcb1, Lhcb2 and Lhcb3 protein isoforms (LHCII), several being substrates of STN7. However, the precise roles of Lhcb phosphorylation during ST remain largely elusive.ResultsWe inactivated the complete Lhcb1 and Lhcb2 gene clades in Arabidopsis thaliana and reintroduced either wild type Lhcb1.3 and Lhcb2.1 isoforms, respectively, or versions lacking N-terminal phosphorylatable residues proposed to mediate state transitions. While the substitution of Lhcb2.1 Thr-40 prevented the formation of the PSI-LHCI-LHCII complex, replacement of Lhcb1.3 Thr-38 did not affect the formation of this supercomplex, nor did influence the amplitude or kinetics of PSII fluorescence quenching upon state 1-state 2 transition.ConclusionsPhosphorylation of Lhcb2 Thr-40 by STN7 alone accounts for ≈ 60% of PSII fluorescence quenching during state transitions. Instead, the presence of Thr-38 phosphosite in Lhcb1.3 was not required for the formation of the PSI-LHCI-LHCII supercomplex nor for re-equilibration of the plastoquinone redox state. The Lhcb2 phosphomutant was still capable of ≈ 40% residual fluorescence quenching, implying that a yet uncharacterized, STN7-dependent, component of state transitions, which is unrelated to Lhcb2 Thr-40 phosphorylation and to the formation of the PSI-LHCI-LHCII supercomplex, contributes to the equilibration of the PSI/PSII excitation pressure upon plastoquinone over-reduction.

Dataset Information

Downregulation of TAP38/PPH1 enables LHCII hyperphosphorylation in Arabidopsis mutant lacking LHCII docking site in PSI.

Publications

Downregulation of TAP38/PPH1 enables LHCII hyperphosphorylation in Arabidopsis mutant lacking LHCII docking site in PSI.

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