Cyanobacteria play a key role in primary production in both oceans and fresh waters and hold great potential for sustainable production of a large number of commodities. During their life, cyanobacteria cells need to acclimate to a multitude of challenges, including shifts in intensity and quality of incident light. Despite our increasing understanding of metabolic regulation under various light regimes, detailed insight into fitness advantages and limitations under shifting light quality remains underexplored. Here, we study photo-physiological acclimation in the cyanobacterium Synechocystis sp. PCC 6803 throughout the photosynthetically active radiation (PAR) range. Using light emitting diodes (LEDs) with qualitatively different narrow spectra, we describe wavelength dependence of light capture, electron transport and energy transduction to main cellular pools. In addition, we describe processes that fine-tune light capture, such as state transitions, or the efficiency of energy transfer from phycobilisomes to photosystems (PS). We show that growth was the most limited under blue light due to inefficient light harvesting, and that many cellular processes are tightly linked to the redox state of the plastoquinone (PQ) pool, which was the most reduced under red light. The PSI-to-PSII ratio was low under blue photons, however, it was not the main growth-limiting factor, since it was even more reduced under violet and near far-red lights, where Synechocystis grew faster compared to blue light. Our results provide insight into the spectral dependence of phototrophic growth and can provide the foundation for future studies of molecular mechanisms underlying light acclimation in cyanobacteria, leading to light optimization in controlled cultivations.

• Klíčová slova
• Cyanobacteria, Light harvesting, Light quality, Photomorphogenesis, Photosynthesis, State transitions,
• MeSH
• aklimatizace * MeSH
• fotosyntéza * fyziologie   MeSH
• fotosystém I - proteinový komplex metabolismus   MeSH
• fotosystém II - proteinový komplex metabolismus   MeSH
• světlo * MeSH
• Synechocystis * fyziologie   účinky záření   metabolismus   růst a vývoj   MeSH
• transport elektronů MeSH
• Publikační typ
• časopisecké články MeSH
• Názvy látek
• fotosystém I - proteinový komplex MeSH
• fotosystém II - proteinový komplex MeSH

Assembly of photosystem II (PSII), a water-splitting catalyst in chloroplasts and cyanobacteria, requires numerous auxiliary proteins which promote individual steps of this sequential process and transiently associate with one or more assembly intermediate complexes. In this study, we focussed on the role of a PSII-associated protein encoded by the ssl1498 gene in the cyanobacterium Synechocystis sp. PCC 6803. The N-terminal domain of this protein, which is here called Psb34, is very similar to the N-terminus of HliA/B proteins belonging to a family of high-light-inducible proteins (Hlips). Psb34 was identified in both dimeric and monomeric PSII, as well as in a PSII monomer lacking CP43 and containing Psb28. When FLAG-tagged, the protein is co-purified with these three complexes and with the PSII auxiliary proteins Psb27 and Psb28. However, the preparation also contained the oxygen-evolving enhancers PsbO and PsbV and lacked HliA/B proteins even when isolated from high-light-treated cells. The data suggest that Psb34 competes with HliA/B for the same binding site and that it is one of the components involved in the final conversion of late PSII assembly intermediates into functional PSII complexes, possibly keeping them free of Hlips. Unlike HliA/B, Psb34 does bind to the CP47 assembly module before its incorporation into PSII. Analysis of strains lacking Psb34 indicates that Psb34 mediates the optimal equilibrium of HliA/B binding among individual PSII assembly intermediates containing CP47, allowing Hlip-mediated photoprotection at all stages of PSII assembly.

• Klíčová slova
• CP47, High-light-inducible protein, Photosynthesis, Photosystem II,
• MeSH
• bakteriální proteiny metabolismus   MeSH
• fotosyntéza MeSH
• fotosystém II - proteinový komplex metabolismus   MeSH
• protein TNFSF14 metabolismus   MeSH
• Synechocystis * metabolismus   MeSH
• Publikační typ
• časopisecké články MeSH
• Názvy látek
• bakteriální proteiny MeSH
• fotosystém II - proteinový komplex MeSH
• protein TNFSF14 MeSH

Light plays an essential role in photosynthesis; however, its excess can cause damage to cellular components. Photosynthetic organisms thus developed a set of photoprotective mechanisms (e.g., non-photochemical quenching, photoinhibition) that can be studied by a classic biochemical and biophysical methods in cell suspension. Here, we combined these bulk methods with single-cell identification of microdomains in thylakoid membrane during high-light (HL) stress. We used Synechocystis sp. PCC 6803 cells with YFP tagged photosystem I. The single-cell data pointed to a three-phase response of cells to acute HL stress. We defined: (1) fast response phase (0-30 min), (2) intermediate phase (30-120 min), and (3) slow acclimation phase (120-360 min). During the first phase, cyanobacterial cells activated photoprotective mechanisms such as photoinhibition and non-photochemical quenching. Later on (during the second phase), we temporarily observed functional decoupling of phycobilisomes and sustained monomerization of photosystem II dimer. Simultaneously, cells also initiated accumulation of carotenoids, especially ɣ-carotene, the main precursor of all carotenoids. In the last phase, in addition to ɣ-carotene, we also observed accumulation of myxoxanthophyll and more even spatial distribution of photosystems and phycobilisomes between microdomains. We suggest that the overall carotenoid increase during HL stress could be involved either in the direct photoprotection (e.g., in ROS scavenging) and/or could play an additional role in maintaining optimal distribution of photosystems in thylakoid membrane to attain efficient photoprotection.

• Klíčová slova
• Synechocystis, carotenoids, high light, microdomains, non-photochemical quenching, photoinhibition, photoprotection, photosystems, thylakoid membrane,
• MeSH
• bakteriální proteiny genetika   metabolismus   MeSH
• fotosystém I - proteinový komplex genetika   metabolismus   MeSH
• fotosystém II - proteinový komplex genetika   metabolismus   MeSH
• karotenoidy metabolismus   MeSH
• světlo * MeSH
• Synechocystis metabolismus   účinky záření   MeSH
• tylakoidy metabolismus   účinky záření   MeSH
• velikost buňky účinky záření   MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• bakteriální proteiny MeSH
• fotosystém I - proteinový komplex MeSH
• fotosystém II - proteinový komplex MeSH
• karotenoidy MeSH