title: Arabidopsis mutants deleted in the light-harvesting protein Lhcb4 have a disrupted photosystem II macrostructure and are defective in photoprotection.
abstract: The role of the light-harvesting complex Lhcb4 (CP29) in photosynthesis was investigated in Arabidopsis thaliana by characterizing knockout lines for each of the three Lhcb4 isoforms (Lhcb4.1/4.2/4.3). Plants lacking all isoforms (koLhcb4) showed a compensatory increase of Lhcb1 and a slightly reduced photosystem II/I ratio with respect to the wild type. The absence of Lhcb4 did not result in alteration in electron transport rates. However, the kinetic of state transition was faster in the mutant, and nonphotochemical quenching activity was lower in koLhcb4 plants with respect to either wild type or mutants retaining a single Lhcb4 isoform. KoLhcb4 plants were more sensitive to photoinhibition, while this effect was not observed in knockout lines for any other photosystem II antenna subunit. Ultrastructural analysis of thylakoid grana membranes showed a lower density of photosystem II complexes in koLhcb4. Moreover, analysis of isolated supercomplexes showed a different overall shape of the C₂S₂ particles due to a different binding mode of the S-trimer to the core complex. An empty space was observed within the photosystem II supercomplex at the Lhcb4 position, implying that the missing Lhcb4 was not replaced by other Lhc subunits. This suggests that Lhcb4 is unique among photosystem II antenna proteins and determinant for photosystem II macro-organization and photoprotection.
authors.affiliation: Dipartimento di Biotecnologie, Università di Verona, 37134 Verona, Italy.
authors.forename: Silvia
authors.initials: S
authors.lastname: de Bianchi
authors.forename: Nico
authors.initials: N
authors.lastname: Betterle
authors.forename: Roman
authors.initials: R
authors.lastname: Kouril
authors.forename: Stefano
authors.initials: S
authors.lastname: Cazzaniga
authors.forename: Egbert
authors.initials: E
authors.lastname: Boekema
authors.forename: Roberto
authors.initials: R
authors.lastname: Bassi
authors.forename: Luca
authors.initials: L
authors.lastname: Dall'Osto
mesh_terms: D017360:Arabidopsis / Q000235:genetics* / Q000502:physiology* / Q000648:ultrastructure*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D002734:Chlorophyll / Q000737:chemistry; D061146:Chlorophyll Binding Proteins / Q000235:genetics / Q000378:metabolism*; D005453:Fluorescence; D055785:Gene Knockdown Techniques; D008027:Light; D015227:Lipid Peroxidation; D008563:Membrane Lipids / Q000737:chemistry / Q000378:metabolism; D010084:Oxidation-Reduction; D018384:Oxidative Stress; D010100:Oxygen / Q000378:metabolism; D010788:Photosynthesis / Q000502:physiology; D045322:Photosynthetic Reaction Center Complex Proteins / Q000235:genetics / Q000378:metabolism; D045331:Photosystem I Protein Complex / Q000378:metabolism; D045332:Photosystem II Protein Complex / Q000378:metabolism / Q000648:ultrastructure*; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism*; D013696:Temperature; D020524:Thylakoids / Q000737:chemistry / Q000378:metabolism / Q000648:ultrastructure
chemical_list: D029681:Arabidopsis Proteins; D061146:Chlorophyll Binding Proteins; C513983:LHCB4.1 protein, Arabidopsis; D008563:Membrane Lipids; D045322:Photosynthetic Reaction Center Complex Proteins; D045331:Photosystem I Protein Complex; D045332:Photosystem II Protein Complex; D020033:Protein Isoforms; D002734:Chlorophyll; D010100:Oxygen