title: The requirement for carotenoids in the assembly and function of the photosynthetic complexes in Chlamydomonas reinhardtii.
abstract: We have investigated the importance of carotenoids on the accumulation and function of the photosynthetic apparatus using a mutant of the green alga Chlamydomonas reinhardtii lacking carotenoids. The FN68 mutant is deficient in phytoene synthase, the first enzyme of the carotenoid biosynthesis pathway, and therefore is unable to synthesize any carotenes and xanthophylls. We find that FN68 is unable to accumulate the light-harvesting complexes associated with both photosystems as well as the RC subunits of photosystem II. The accumulation of the cytochrome b₆f complex is also strongly reduced to a level approximately 10% that of the wild type. However, the residual fraction of assembled cytochrome b₆f complexes exhibits single-turnover electron transfer kinetics comparable to those observed in the wild-type strain. Surprisingly, photosystem I is assembled to significant levels in the absence of carotenoids in FN68 and possesses functional properties that are very similar to those of the wild-type complex.
authors.affiliation: Institute of Structural and Molecular Biology, University College London, London WC1E 6BT, United Kingdom. stefano.santabarbara@cnr.it
authors.forename: Stefano
authors.initials: S
authors.lastname: Santabarbara
authors.forename: Anna Paola
authors.initials: AP
authors.lastname: Casazza
authors.forename: Kulsam
authors.initials: K
authors.lastname: Ali
authors.forename: Chloe K
authors.initials: CK
authors.lastname: Economou
authors.forename: Thanyanun
authors.initials: T
authors.lastname: Wannathong
authors.forename: Francesca
authors.initials: F
authors.lastname: Zito
authors.forename: Kevin E
authors.initials: KE
authors.lastname: Redding
authors.forename: Fabrice
authors.initials: F
authors.lastname: Rappaport
authors.forename: Saul
authors.initials: S
authors.lastname: Purton
mesh_terms: D019883:Alkyl and Aryl Transferases / Q000235:genetics / Q000378:metabolism; D002338:Carotenoids / Q000235:genetics / Q000378:metabolism*; D016825:Chlamydomonas reinhardtii / Q000201:enzymology* / Q000235:genetics; D045346:Cytochrome b6f Complex / Q000235:genetics / Q000378:metabolism; D004578:Electron Spin Resonance Spectroscopy / Q000379:methods; D004579:Electron Transport; D051232:Geranylgeranyl-Diphosphate Geranylgeranyltransferase; D008027:Light; D009154:Mutation; D010084:Oxidation-Reduction; D010641:Phenotype; D045331:Photosystem I Protein Complex / Q000235:genetics / Q000378:metabolism; D045332:Photosystem II Protein Complex / Q000235:genetics / Q000378:metabolism*; D021381:Protein Transport; D020524:Thylakoids / Q000201:enzymology / Q000235:genetics / Q000378:metabolism; D014170:Transformation, Genetic
chemical_list: D045331:Photosystem I Protein Complex; D045332:Photosystem II Protein Complex; D002338:Carotenoids; D045346:Cytochrome b6f Complex; D019883:Alkyl and Aryl Transferases; D051232:Geranylgeranyl-Diphosphate Geranylgeranyltransferase