title: Carotenoids are essential for the assembly of cyanobacterial photosynthetic complexes.
abstract: In photosynthetic organisms, carotenoids (carotenes and xanthophylls) are important for light harvesting, photoprotection and structural stability of a variety of pigment-protein complexes. Here, we investigated the consequences of altered carotenoid composition for the functional organization of photosynthetic complexes in wild-type and various mutant strains of the cyanobacterium Synechocystis sp. PCC 6803. Although it is generally accepted that xanthophylls do not play a role in cyanobacterial photosynthesis in low-light conditions, we have found that the absence of xanthophylls leads to reduced oligomerization of photosystems I and II. This is remarkable because these complexes do not bind xanthophylls. Oligomerization is even more disturbed in crtH mutant cells, which show limited carotenoid synthesis; in these cells also the phycobilisomes are distorted despite the fact that these extramembranous light-harvesting complexes do not contain carotenoids. The number of phycocyanin rods connected to the phycobilisome core is strongly reduced leading to high amounts of unattached phycocyanin units. In the absence of carotenoids the overall organization of the thylakoid membranes is disturbed: Photosystem II is not formed, photosystem I hardly oligomerizes and the assembly of phycobilisomes remains incomplete. These data underline the importance of carotenoids in the structural and functional organization of the cyanobacterial photosynthetic machinery.
authors.affiliation: Institute of Plant Biology, Biological Research Centre, Hungarian Academy of Sciences, P.O. Box 521, H-6701 Szeged, Hungary; Laboratory of Biophysics, Wageningen University, P.O. Box 8128, 6700 ET Wageningen, The Netherlands. Electronic address: toth.tunde@brc.mta.hu.
authors.forename: Tünde N
authors.initials: TN
authors.lastname: Tóth
authors.affiliation: Laboratory of Biophysics, Wageningen University, P.O. Box 8128, 6700 ET Wageningen, The Netherlands. Electronic address: chukhutsina@gmail.com.
authors.forename: Volha
authors.initials: V
authors.lastname: Chukhutsina
authors.affiliation: Institute of Plant Biology, Biological Research Centre, Hungarian Academy of Sciences, P.O. Box 521, H-6701 Szeged, Hungary. Electronic address: domonkos.ildiko@brc.mta.hu.
authors.forename: Ildikó
authors.initials: I
authors.lastname: Domonkos
authors.affiliation: Laboratory of Photosynthesis, Center Algatech, Institute of Microbiology, Academy of Sciences, Opatovicky mlyn, 37981 Trebon, Czech Republic; Faculty of Science, University of South Bohemia, Branisovska 31, 37005 Ceske Budejovice, Czech Republic. Electronic address: knoppova@alga.cz.
authors.forename: Jana
authors.initials: J
authors.lastname: Knoppová
authors.affiliation: Laboratory of Photosynthesis, Center Algatech, Institute of Microbiology, Academy of Sciences, Opatovicky mlyn, 37981 Trebon, Czech Republic; Faculty of Science, University of South Bohemia, Branisovska 31, 37005 Ceske Budejovice, Czech Republic. Electronic address: komenda@alga.cz.
authors.forename: Josef
authors.initials: J
authors.lastname: Komenda
authors.affiliation: Institute of Plant Biology, Biological Research Centre, Hungarian Academy of Sciences, P.O. Box 521, H-6701 Szeged, Hungary. Electronic address: kis.mihaly@brc.mta.hu.
authors.forename: Mihály
authors.initials: M
authors.lastname: Kis
authors.affiliation: Institute of Plant Biology, Biological Research Centre, Hungarian Academy of Sciences, P.O. Box 521, H-6701 Szeged, Hungary. Electronic address: zsofia.lenart@gmail.com.
authors.forename: Zsófia
authors.initials: Z
authors.lastname: Lénárt
authors.affiliation: Institute of Plant Biology, Biological Research Centre, Hungarian Academy of Sciences, P.O. Box 521, H-6701 Szeged, Hungary. Electronic address: garab.gyozo@brc.mta.hu.
authors.forename: Győző
authors.initials: G
authors.lastname: Garab
authors.affiliation: Institute of Plant Biology, Biological Research Centre, Hungarian Academy of Sciences, P.O. Box 521, H-6701 Szeged, Hungary. Electronic address: kovacs.laszlo@brc.mta.hu.
authors.forename: László
authors.initials: L
authors.lastname: Kovács
authors.affiliation: Institute of Plant Biology, Biological Research Centre, Hungarian Academy of Sciences, P.O. Box 521, H-6701 Szeged, Hungary. Electronic address: gombos.zoltan@brc.mta.hu.
authors.forename: Zoltán
authors.initials: Z
authors.lastname: Gombos
authors.affiliation: Laboratory of Biophysics, Wageningen University, P.O. Box 8128, 6700 ET Wageningen, The Netherlands; MicroSpectroscopy Centre, Wageningen University, P.O. Box 8128, 6700 ET Wageningen, The Netherlands. Electronic address: herbert.vanamerongen@wur.nl.
authors.forename: Herbert
authors.initials: H
authors.lastname: van Amerongen
keywords: Carotenoid deficiency; Cyanobacterial photosynthesis; Photosynthetic complexes; Phycobilisome; Time-resolved fluorescence