Vol.:(0123456789) 1 3 Photosynthesis Research https://doi.org/10.1007/s11120-020-00776-1 ORIGINAL ARTICLE Phycobilisome integrity and functionality in lipid unsaturation and xanthophyll mutants in Synechocystis Sindhujaa Vajravel 1,2  · Hajnalka Laczkó‑Dobos 3  · Nia Petrova 4  · Éva Herman 1  · Terézia Kovács 1,5  · Tomas Zakar 1,6  · Svetla Todinova 4  · Stefka Taneva 4  · Lászlo Kovács 1  · Zoltan Gombos 1  · Tünde Tóth 1  · Sashka Krumova 4 Received: 24 March 2020 / Accepted: 19 July 2020 © Springer Nature B.V. 2020 Abstract The major light-harvesting system in cyanobacteria, the phycobilisome, is an essential component of the photosynthetic apparatus that regulates the utilization of the natural light source—the Sun. Earlier works revealed that the thylakoid mem- brane composition and its physical properties might have an important role in antennas docking. Polyunsaturated lipids and xanthophylls are among the most signifcant modulators of the physical properties of thylakoid membranes. In the nature, the action of these molecules is orchestrated in response to environmental stimuli among which the growth temperature is the most infuential. In order to further clarify the signifcance of thylakoid membrane physical properties for the phycobilisomes assembly (i.e. structural integrity) and their ability to efciently direct the excitation energy towards the photosynthetic com- plexes, in this work, we utilize cyanobacterial Synechocystis sp. PCC 6803 mutants defcient in polyunsaturated lipids (AD mutant) and xanthophylls (RO mutant), as well as a strain depleted of both xanthophylls and polyunsaturated lipids (ROAD multiple mutant). For the frst time, we discuss the efect of those mutations on the phycobilisomes assembly, integrity and functionality at optimal (30 °C) and moderate low (25 °C) and high (35 °C) temperatures. Our results show that xanthophyll depletion exerts a much stronger efect on both phycobilisome’s integrity and the response of cells to growth at suboptimal temperatures than lipid unsaturation level. The strongest efects were observed for the combined ROAD mutant, which exhibited thermally destabilized phycobilisomes and a population of energetically uncoupled phycocyanin units. Keywords Phycobilisome · Cyanobacteria · Lipid unsaturation · Carotenoids · Excitation energy transfer · Thermal stability Introduction Light harvesting in cyanobacteria strongly relies on the peripheral antenna complex—the phycobilisome (PBS). The general organization of this multi-component structure consists of several phycocyanin, phycoerythrin or phyco- erythrocyanin rods, attached to two to fve allophycocyanin core cylinders that are able to physically interact with the two photosystems embedded into the thylakoid membrane (Arteni et al. 2009; Liu et al. 2013; Blankenship 2015; Chang et al. 2015; Tal et al. 2014). Liu et al. (2013) demon- strated that PBSs are able to form a megacomplex together with photosystem I (PSI) and II (PSII) that ensures efcient energy trapping by the reaction centers. Several studies also strongly suggest that the rods of PBSs might interact with more than one PBS core and therefore most probably there are no unique but rather several possible models of structural organization of PBSs (Collins et al. 2012; David et al. 2014). * Sashka Krumova sashka.b.krumova@gmail.com 1 Institute of Plant Biology, Biological Research Centre, Szeged, Hungary 2 Molecular Plant Biology, Department of Biochemistry, University of Turku, Turku, Finland 3 Institute of Genetics, Biological Research Centre, Szeged, Hungary 4 Institute of Biophysics and Biomedical Engineering, Bulgarian Academy of Sciences, Sofa, Bulgaria 5 Department of Plant Biology, University of Szeged, Szeged, Hungary 6 Institute of Photonics and Electronics, The Czech Academy of Sciences, Prague, Czech Republic