title: Double mutation cpSRP43--/cpSRP54-- is necessary to abolish the cpSRP pathway required for thylakoid targeting of the light-harvesting chlorophyll proteins.
abstract: Biochemical and genetic studies have established that the light-harvesting chlorophyll proteins (LHCPs) of the photosystems use the cpSRP (chloroplast signal recognition particle) pathway for their targeting to thylakoids. Previous analyses of single cpSRP mutants, chaos and ffc, deficient in cpSRP43 and cpSRP54, respectively, have revealed that half of the LHCPs are still integrated into the thylakoid membranes. Surprisingly, the effects of both mutations are additive in the double mutant ffc/chaos described here. This mutant has pale yellow leaves at all stages of growth and drastically reduced levels of all the LHCPs except Lhcb 4. Although the chloroplasts have a normal shape, the thylakoid structure is affected by the mutation, probably as a consequence of reduction of all the LHCPs. ELIPs (early light-inducible proteins), nuclear-encoded proteins related to the LHCP family and inducible by light stress, were also drastically reduced in the double mutant. However, proteins targeted by other chloroplastic targeting pathways (DeltapH, Sec and spontaneous pathways) accumulated to similar levels in the wild-type and the double mutant. Therefore, the near total loss of LHCPs and ELIPs in the double mutant suggests that cpSRP is the predominant, if not exclusive, targeting pathway for these proteins. Phenotypic analysis of the double mutant, compared to the single mutants, suggests that the cpSRP subunits cpSRP43 and cpSRP54 contribute to antenna targeting in an independent but additive way.
authors.affiliation: Laboratoire du Métabolisme Carboné, UMR 163 CNRS/CEA, Univ-Méditerranée UMR 163, DSV, DEVM, CEA/CADARACHE, F-13108 St Paul lez Durance Cedex, France.
authors.forename: Claire
authors.initials: C
authors.lastname: Hutin
authors.forename: Michel
authors.initials: M
authors.lastname: Havaux
authors.forename: Jean-Pierre
authors.initials: JP
authors.lastname: Carde
authors.forename: Klaus
authors.initials: K
authors.lastname: Kloppstech
authors.forename: Karin
authors.initials: K
authors.lastname: Meiherhoff
authors.forename: Neil
authors.initials: N
authors.lastname: Hoffman
authors.forename: Laurent
authors.initials: L
authors.lastname: Nussaume
mesh_terms: D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism / Q000648:ultrastructure; D029681:Arabidopsis Proteins; D002734:Chlorophyll / Q000528:radiation effects; D060365:Chloroplast Proteins; D045342:Light-Harvesting Protein Complexes; D008854:Microscopy, Electron; D009154:Mutation; D010641:Phenotype; D045322:Photosynthetic Reaction Center Complex Proteins / Q000378:metabolism*; D010940:Plant Proteins / Q000235:genetics* / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins; D018271:Signal Recognition Particle / Q000235:genetics* / Q000378:metabolism / Q000648:ultrastructure; D020524:Thylakoids / Q000378:metabolism* / Q000648:ultrastructure
chemical_list: D029681:Arabidopsis Proteins; D060365:Chloroplast Proteins; C078410:ELIP protein, Arabidopsis; C083707:FFC protein, Arabidopsis; D045342:Light-Harvesting Protein Complexes; D045322:Photosynthetic Reaction Center Complex Proteins; D010940:Plant Proteins; C069268:SRP54 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D018271:Signal Recognition Particle; D002734:Chlorophyll