title: The photosystem II light-harvesting protein Lhcb3 affects the macrostructure of photosystem II and the rate of state transitions in Arabidopsis.
abstract: The main trimeric light-harvesting complex of higher plants (LHCII) consists of three different Lhcb proteins (Lhcb1-3). We show that Arabidopsis thaliana T-DNA knockout plants lacking Lhcb3 (koLhcb3) compensate for the lack of Lhcb3 by producing increased amounts of Lhcb1 and Lhcb2. As in wild-type plants, LHCII-photosystem II (PSII) supercomplexes were present in Lhcb3 knockout plants (koLhcb3), and preservation of the LHCII trimers (M trimers) indicates that the Lhcb3 in M trimers has been replaced by Lhcb1 and/or Lhcb2. However, the rotational position of the M LHCII trimer was altered, suggesting that the Lhcb3 subunit affects the macrostructural arrangement of the LHCII antenna. The absence of Lhcb3 did not result in any significant alteration in PSII efficiency or qE type of nonphotochemical quenching, but the rate of transition from State 1 to State 2 was increased in koLhcb3, although the final extent of state transition was unchanged. The level of phosphorylation of LHCII was increased in the koLhcb3 plants compared with wild-type plants in both State 1 and State 2. The relative increase in phosphorylation upon transition from State 1 to State 2 was also significantly higher in koLhcb3. It is suggested that the main function of Lhcb3 is to modulate the rate of state transitions.
authors.affiliation: Umeå Plant Science Centre, Department of Plant Physiology, Umeå University, SE-90187 Umeå, Sweden.
authors.forename: Jakob T
authors.initials: JT
authors.lastname: Damkjaer
authors.forename: Sami
authors.initials: S
authors.lastname: Kereïche
authors.forename: Matthew P
authors.initials: MP
authors.lastname: Johnson
authors.forename: Laszlo
authors.initials: L
authors.lastname: Kovacs
authors.forename: Anett Z
authors.initials: AZ
authors.lastname: Kiss
authors.forename: Egbert J
authors.initials: EJ
authors.lastname: Boekema
authors.forename: Alexander V
authors.initials: AV
authors.lastname: Ruban
authors.forename: Peter
authors.initials: P
authors.lastname: Horton
authors.forename: Stefan
authors.initials: S
authors.lastname: Jansson
mesh_terms: D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism* / Q000648:ultrastructure; D029681:Arabidopsis Proteins / Q000235:genetics / Q000502:physiology*; D045342:Light-Harvesting Protein Complexes / Q000235:genetics / Q000502:physiology*; D008854:Microscopy, Electron; D008969:Molecular Sequence Data; D045332:Photosystem II Protein Complex / Q000235:genetics / Q000378:metabolism* / Q000648:ultrastructure; D030821:Plants, Genetically Modified / Q000235:genetics / Q000378:metabolism / Q000648:ultrastructure
chemical_list: D029681:Arabidopsis Proteins; D045342:Light-Harvesting Protein Complexes; D045332:Photosystem II Protein Complex