title: Light-harvesting II antenna trimers connect energetically the entire photosynthetic machinery - including both photosystems II and I.
abstract: In plant chloroplasts, the two photosystems (PSII and PSI) are enriched in different thylakoid domains and, according to the established view, are regarded as energetically segregated from each other. A specific fraction of the light harvesting complex II (LHCII) has been postulated to get phosphorylated by the STN7 kinase and subsequently to migrate from PSII to PSI as part of a process called 'state transition'. Nevertheless, the thylakoid membrane incorporates a large excess of LHCII not present in the isolatable PSII-LHCII and PSI-LHCII complexes. Moreover, LHCII phosphorylation is not limited to a specific LHCII pool and "state 2" condition, but is found in all thylakoid domains in any constant light condition. Here, using a targeted solubilization of pigment-protein complexes from different thylakoid domains, we demonstrate that even a minor detachment of LHCII leads to markedly increased fluorescence emission from LHCII and PSII both in grana core and non-appressed thylakoid membranes and the effect of the detergent to detach LHCII is enhanced in the absence of LHCII phosphorylation. These findings provide evidence that PSII and PSI are energy traps embedded in the same energetically connected LHCII lake. In the lake, PSI and LHCII are energetically connected even in the absence of LHCII phosphorylation, yet the phosphorylation enhances the interaction required for efficient energy transfer to PSI in the grana margin regions.
authors.affiliation: Molecular Plant Biology, Department of Biochemistry, University of Turku, FIN-20014 Turku, Finland.
authors.forename: Michele
authors.initials: M
authors.lastname: Grieco
authors.affiliation: Molecular Plant Biology, Department of Biochemistry, University of Turku, FIN-20014 Turku, Finland.
authors.forename: Marjaana
authors.initials: M
authors.lastname: Suorsa
authors.affiliation: School of Life Science, Devi Ahilya University, Indore 452017, MP, India.
authors.forename: Anjana
authors.initials: A
authors.lastname: Jajoo
authors.affiliation: Molecular Plant Biology, Department of Biochemistry, University of Turku, FIN-20014 Turku, Finland.
authors.forename: Mikko
authors.initials: M
authors.lastname: Tikkanen
authors.affiliation: Molecular Plant Biology, Department of Biochemistry, University of Turku, FIN-20014 Turku, Finland. Electronic address: evaaro@utu.fi.
authors.forename: Eva-Mari
authors.initials: EM
authors.lastname: Aro
mesh_terms: D017360:Arabidopsis / Q000378:metabolism*; D002734:Chlorophyll / Q000378:metabolism; D002736:Chloroplasts / Q000378:metabolism; D004735:Energy Transfer; D005453:Fluorescence; D008027:Light; D045342:Light-Harvesting Protein Complexes / Q000378:metabolism*; D010766:Phosphorylation; D010788:Photosynthesis; D045331:Photosystem I Protein Complex / Q000378:metabolism*; D045332:Photosystem II Protein Complex / Q000378:metabolism*; D030821:Plants, Genetically Modified / Q000378:metabolism*; D020524:Thylakoids / Q000378:metabolism*
chemical_list: D045342:Light-Harvesting Protein Complexes; D045331:Photosystem I Protein Complex; D045332:Photosystem II Protein Complex; D002734:Chlorophyll
keywords: Energy spillover; Extra LHCII; Lateral heterogeneity; Protein phosphorylation; State transitions; Thylakoid membrane