title: PsbN is required for assembly of the photosystem II reaction center in Nicotiana tabacum.
abstract: The chloroplast-encoded low molecular weight protein PsbN is annotated as a photosystem II (PSII) subunit. To elucidate the localization and function of PsbN, encoded on the opposite strand to the psbB gene cluster, we raised antibodies and inserted a resistance cassette into PsbN in both directions. Both homoplastomic tobacco (Nicotiana tabacum) mutants psbN-F and psbN-R show essentially the same PSII deficiencies. The mutants are extremely light sensitive and failed to recover from photoinhibition. Although synthesis of PSII proteins was not altered significantly, both mutants accumulated only ∼25% of PSII proteins compared with the wild type. Assembly of PSII precomplexes occurred at normal rates, but heterodimeric PSII reaction centers (RCs) and higher order PSII assemblies were not formed efficiently in the mutants. The psbN-R mutant was complemented by allotopic expression of the PsbN gene fused to the sequence of a chloroplast transit peptide in the nuclear genome. PsbN represents a bitopic trans-membrane peptide localized in stroma lamellae with its highly conserved C terminus exposed to the stroma. Significant amounts of PsbN were already present in dark-grown seedling. Our data prove that PsbN is not a constituent subunit of PSII but is required for repair from photoinhibition and efficient assembly of the PSII RC.
authors.affiliation: Biozentrum der Ludwig-Maximilians-Universität München, Department Biologie I, 82152 Planegg-Martinsried, Germany.
authors.forename: Salar
authors.initials: S
authors.lastname: Torabi
authors.forename: Pavan
authors.initials: P
authors.lastname: Umate
authors.forename: Nikolay
authors.initials: N
authors.lastname: Manavski
authors.forename: Magdalena
authors.initials: M
authors.lastname: Plöchinger
authors.forename: Laura
authors.initials: L
authors.lastname: Kleinknecht
authors.forename: Hanumakumar
authors.initials: H
authors.lastname: Bogireddi
authors.forename: Reinhold G
authors.initials: RG
authors.lastname: Herrmann
authors.forename: Gerhard
authors.initials: G
authors.lastname: Wanner
authors.forename: Wolfgang P
authors.initials: WP
authors.lastname: Schröder
authors.forename: Jörg
authors.initials: J
authors.lastname: Meurer
mesh_terms: D020869:Gene Expression Profiling; D018506:Gene Expression Regulation, Plant / Q000528:radiation effects; D017343:Genes, Plant; D008027:Light; D009154:Mutation; D009876:Operon; D045332:Photosystem II Protein Complex / Q000378:metabolism*; D010940:Plant Proteins / Q000502:physiology*; D014026:Nicotiana / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic
chemical_list: D045332:Photosystem II Protein Complex; D010940:Plant Proteins