Caractérisations biochimiques et génétiques des complexes pigment-protéines dans le procaryote marin Prochlorococcus : origine évolutive et rôle dans l'adaptation phosynthétique aux conditions lumineuses

Laurence Garczarek 1
1 MAPP - MArine Phototrophic Prokaryotes
ADMM - Adaptation et diversité en milieu marin
Abstract : The pigment-protein complexes of the photosynthetic apparatus play a major role in the capacity of adaptation to light environment of oxyphototrophic organisms. In order to better understand the mechanisms involved in both photoacclimation (in the physiological sense) and photoadaptation (in the evolutive sense) processes, this study used as a model organism the marine prokaryote Prochlorococcus, which in the field is able to sustain growth and photosynthesis over almost four orders of magnitude of light. The biochemical characterization of the photosystem I has shown that the reaction center I can bind some Chl b and that some minor proteins highly diverge from those of typical cyanobacteria containing phycobilisomes. Since this photosystem is particularly conserved within oxyphototrophic organisms, these modifications likely have implications on the biophysical and biochemical properties of this photosystem. The most remarkable peculiarity of the photosynthetic apparatus of Prochloroccus is certainly the multiplication of genes encoding the major light harvesting antenna (pcb) in low-sight strains (5-7 copies), whereas only a single pcb copy is present in high-light adapted strains. This phenomenon, which probably results from a long term adaptation to different light niches in the ocean, is certainly one of the main factors responsible for the differences observed between the Prochlorococcus ecotypes at both the pigment and physiological levels. The expression pattern at the transcriptional level of several genes encoding photosynthetic proteins (pcb, psbA, psbC, psbD) is also typical and suggest the occurrence of a regulation process of light absorption specific from Prochlorococcus. In the last part of this phD, the structural comparison of Prochlorococcus antenna with other Chl-binding proteins of the photosynthetic apparatus and the analysis of the MED4 genome led us to re-examine the relationships between the antenna complexes of eukaryotes and Chl b-containing prokaryotes as well as the major subunits of the reaction center I.
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Laurence Garczarek. Caractérisations biochimiques et génétiques des complexes pigment-protéines dans le procaryote marin Prochlorococcus : origine évolutive et rôle dans l'adaptation phosynthétique aux conditions lumineuses. Biochimie, Biologie Moléculaire. Institut National Agronomique de Paris-Grignon, 2000. Français. ⟨tel-01115741⟩

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