title: Characterization of the photosynthetic apparatus of the Eustigmatophycean Nannochloropsis gaditana: evidence of convergent evolution in the supramolecular organization of photosystem I.
abstract: Nannochloropsis gaditana belongs to Eustigmatophyceae, a class of eukaryotic algae resulting from a secondary endosymbiotic event. Species of this class have been poorly characterized thus far but are now raising increasing interest in the scientific community because of their possible application in biofuel production. Nannochloropsis species have a peculiar photosynthetic apparatus characterized by the presence of only chlorophyll a, with violaxanthin and vaucheriaxanthin esters as the most abundant carotenoids. In this study, the photosynthetic apparatus of this species was analyzed by purifying the thylakoids and isolating the different pigment-binding complexes upon mild solubilization. The results from the biochemical and spectroscopic characterization showed that the photosystem II antenna is loosely bound to the reaction center, whereas the association is stronger in photosystem I, with the antenna-reaction center super-complexes surviving purification. Such a supramolecular organization was found to be conserved in photosystem I from several other photosynthetic eukaryotes, even though these taxa are evolutionarily distant. A hypothesis on the possible selective advantage of different associations of the antenna complexes of photosystems I and II is discussed.
authors: Dipartimento di Biologia, Università di Padova, Italy.
authors: Stefania
authors: S
authors: Basso
authors: Dipartimento di Biologia, Università di Padova, Italy.
authors: Diana
authors: D
authors: Simionato
authors: Dipartimento di Biologia, Università di Padova, Italy.
authors: Caterina
authors: C
authors: Gerotto
authors: Dipartimento di Biologia, Università di Padova, Italy.
authors: Anna
authors: A
authors: Segalla
authors: Dipartimento di Biologia, Università di Padova, Italy.
authors: Giorgio M
authors: GM
authors: Giacometti
authors: Dipartimento di Biologia, Università di Padova, Italy. Electronic address: tomas.morosinotto@unipd.it.
authors: Tomas
authors: T
authors: Morosinotto
mesh_terms: D000042:Absorption; D002338:Carotenoids / Q000378:metabolism; D002499:Centrifugation, Density Gradient; D019143:Evolution, Molecular; D045342:Light-Harvesting Protein Complexes / Q000378:metabolism; D010455:Peptides / Q000378:metabolism; D010788:Photosynthesis; D045331:Photosystem I Protein Complex / Q000378:metabolism*; D045332:Photosystem II Protein Complex / Q000378:metabolism; D011485:Protein Binding; D013050:Spectrometry, Fluorescence; D058009:Stramenopiles / Q000378:metabolism*; D024341:Xanthophylls / Q000378:metabolism
chemical_list: D045342:Light-Harvesting Protein Complexes; D010455:Peptides; D045331:Photosystem I Protein Complex; D045332:Photosystem II Protein Complex; D024341:Xanthophylls; D002338:Carotenoids; C005613:violaxanthin
keywords: Heterokonta; Light-harvesting complex; Photosynthesis; Photosynthetic apparatus; Photosystem; Thylakoid