title: Occurrence and function of the orange carotenoid protein in photoprotective mechanisms in various cyanobacteria.
abstract: Excess light is harmful for photosynthetic organisms. The cyanobacterium Synechocystis PCC 6803 protects itself by dissipating the excess of energy absorbed by the phycobilisome, the water-soluble antenna of Photosystem II, into heat decreasing the excess energy arriving to the reaction centers. Energy dissipation results in a detectable decrease of fluorescence. The soluble Orange Carotenoid Protein (OCP) is essential for this blue-green light induced mechanism. OCP genes appear to be highly conserved among phycobilisome-containing cyanobacteria with few exceptions. Here, we show that only the strains containing a whole OCP gene can perform a blue-light induced photoprotective mechanism under both iron-replete and iron-starvation conditions. In contrast, strains containing only N-terminal and/or C-terminal OCP-like genes, or no OCP-like genes at all lack this light induced photoprotective mechanism and they were more sensitive to high-light illumination. These strains must adopt a different strategy to longer survive under stress conditions. Under iron starvation, the relative decrease of phycobiliproteins was larger in these strains than in the OCP-containing strains, avoiding the appearance of a population of dangerous, functionally disconnected phycobilisomes. The OCP-containing strains protect themselves from high light, notably under conditions inducing the appearance of disconnected phycobilisomes, using the energy dissipation OCP-phycobilisome mechanism.
authors.affiliation: Commissariat à l'Energie Atomique (CEA), Institut de Biologie et Technologies de Saclay (iBiTec-S) and Centre National de la Recherche Scientifique (CNRS), Gif sur Yvette, France.
authors.forename: Clémence
authors.initials: C
authors.lastname: Boulay
authors.forename: Leyla
authors.initials: L
authors.lastname: Abasova
authors.forename: Christophe
authors.initials: C
authors.lastname: Six
authors.forename: Imre
authors.initials: I
authors.lastname: Vass
authors.forename: Diana
authors.initials: D
authors.lastname: Kirilovsky
mesh_terms: D017033:Anabaena / Q000235:genetics / Q000378:metabolism; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D000458:Cyanobacteria / Q000235:genetics / Q000378:metabolism*; D007501:Iron / Q000378:metabolism; D008027:Light; D010788:Photosynthesis / Q000502:physiology; D045332:Photosystem II Protein Complex / Q000378:metabolism; D045524:Phycobilisomes / Q000378:metabolism; D046940:Synechococcus / Q000235:genetics / Q000378:metabolism; D046939:Synechocystis / Q000235:genetics / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D045332:Photosystem II Protein Complex; D045524:Phycobilisomes; C109473:orange carotenoid protein, Synechocystis; D007501:Iron