title: Lack of the light-harvesting complex CP24 affects the structure and function of the grana membranes of higher plant chloroplasts.
abstract: The photosystem II (PSII) light-harvesting antenna in higher plants contains a number of highly conserved gene products whose function is unknown. Arabidopsis thaliana plants depleted of one of these, the CP24 light-harvesting complex, have been analyzed. CP24-deficient plants showed a decrease in light-limited photosynthetic rate and growth, but the pigment and protein content of the thylakoid membranes were otherwise almost unchanged. However, there was a major change in the macroorganization of PSII within these membranes; electron microscopy and image analysis revealed the complete absence of the C(2)S(2)M(2) light-harvesting complex II (LHCII)/PSII supercomplex predominant in wild-type plants. Instead, only C(2)S(2) supercomplexes, which are deficient in the LHCIIb M-trimers, were found. Spectroscopic analysis confirmed the disruption of the wild-type macroorganization of PSII. It was found that the functions of the PSII antenna were disturbed: connectivity between PSII centers was reduced, and maximum photochemical yield was lowered; rapidly reversible nonphotochemical quenching was inhibited; and the state transitions were altered kinetically. CP24 is therefore an important factor in determining the structure and function of the PSII light-harvesting antenna, providing the linker for association of the M-trimer into the PSII complex, allowing a specific macroorganization that is necessary both for maximum quantum efficiency and for photoprotective dissipation of excess excitation energy.
authors.affiliation: Department of Molecular Biology and Biotechnology, University of Sheffield, Sheffield S10 2TN, UK.
authors.forename: László
authors.initials: L
authors.lastname: Kovács
authors.forename: Jakob
authors.initials: J
authors.lastname: Damkjaer
authors.forename: Sami
authors.initials: S
authors.lastname: Kereïche
authors.forename: Cristian
authors.initials: C
authors.lastname: Ilioaia
authors.forename: Alexander V
authors.initials: AV
authors.lastname: Ruban
authors.forename: Egbert J
authors.initials: EJ
authors.lastname: Boekema
authors.forename: Stefan
authors.initials: S
authors.lastname: Jansson
authors.forename: Peter
authors.initials: P
authors.lastname: Horton
mesh_terms: D017360:Arabidopsis / Q000378:metabolism* / Q000528:radiation effects / Q000648:ultrastructure; D029681:Arabidopsis Proteins / Q000032:analysis / Q000302:isolation & purification / Q000378:metabolism*; D002736:Chloroplasts / Q000648:ultrastructure*; D002850:Chromatography, Gel; D002942:Circular Dichroism; D004269:DNA, Bacterial / Q000378:metabolism; D005453:Fluorescence; D008027:Light; D045342:Light-Harvesting Protein Complexes / Q000032:analysis / Q000172:deficiency* / Q000302:isolation & purification; D008954:Models, Biological; D016254:Mutagenesis, Insertional; D010788:Photosynthesis / Q000528:radiation effects; D045322:Photosynthetic Reaction Center Complex Proteins / Q000378:metabolism; D045332:Photosystem II Protein Complex / Q000378:metabolism; D010860:Pigments, Biological / Q000378:metabolism; D018515:Plant Leaves / Q000528:radiation effects; D016372:RNA, Antisense / Q000378:metabolism; D013329:Structure-Activity Relationship; D013696:Temperature; D020524:Thylakoids / Q000648:ultrastructure*
chemical_list: D029681:Arabidopsis Proteins; D004269:DNA, Bacterial; D045342:Light-Harvesting Protein Complexes; C489731:NPQ4 protein, Arabidopsis; D045322:Photosynthetic Reaction Center Complex Proteins; D045332:Photosystem II Protein Complex; D010860:Pigments, Biological; D016372:RNA, Antisense; C036483:T-DNA