Cyanobacteria have been widely used as model organisms in photobiochemical research and have recently been exploited as hosts in numerous pilot studies to produce valuable biochemicals via genetic and metabolic modifications. Analyzing cellular RNA is a suitable method for studying genetic changes in cells. Several methods have previously been reported for cyanobacterial RNA extraction. However, the majority of these methods rely heavily on phenol and chloroform, which are hazardous. Additionally, these methods are time-consuming and difficult to perform. Using Synechocystis sp. PCC 6803 as a model, this study developed a novel method for extracting total ribonucleic acid (RNA) using standard centrifugation techniques and laboratory chemicals such as citric acid, ethylenediaminetetraacetic acid, sodium dodecyl sulfate, sodium chloride, and tri-sodium citrate dihydrate to extract RNA from cyanobacterial cells. This method does not necessitate the use of hazardous chemicals, especially phenol and chloroform. Furthermore, it is cost-effective since it does not require expensive chemicals. The results of the quantification, purity, and integrity checks show the effectiveness of this method for extracting good-quality RNA. Furthermore, RT-qPCR results demonstrate that the quality of the extracted RNA is suitable for downstream applications.

The D2 protein of Photosystem II has five transmembrane helices (A-E). An extended loop, connecting helices D and E, contributes to the binding environments of the primary quinone electron acceptor Q(A), and that of the bicarbonate bound to the non-heme iron between Q(A) and the secondary quinone electron acceptor Q(B). The residues from Ala240 to Thr243 are within a conserved sequence ((240)AEETYSMVTAN(250)) that contributes to the stabilization of both Q(A) and bicarbonate. We have created the A240D, E241A, E242A, E242D and T243A mutants to study the role of these residues. The mutations in the A240D and E241A strains had little impact on PS II performance, except addition of formate altered chlorophyll a fluorescence decay in the E241A mutant following a single-turnover actinic flash. Measurements of variable chlorophyll a fluorescence and thermoluminescence showed the E242A and E242D mutants had impaired acceptor side electron transport consistent with a reduced redox gap between Q(A) and Q(B). In addition, the T243A mutant exhibited a heightened susceptibility to photodamage. These data show that mutations introduced between (241)Glu-Thr(243) of D2 impair PS II activity but are less detrimental than mutations between the corresponding (243)Glu-Thr(245) residues of D1 in the vicinity of the Q(B)-binding site.

All cyanobacteria, algae, and plants utilize a common water-oxidizing catalyst to drive the OER during photosynthesis. This catalyst, known as the WOC or OEC of PSII, features a MnCa cluster that carries out the OER with exceptional efficiency. The OER is not only fundamental to natural photosynthesis but is also recognized as a critical reaction in the context of artificial photosynthesis. Artificial photosynthesis holds great promise for sustainable energy solutions by potentially providing an inexpensive source of electrons derived from water. These electrons could be utilized for hydrogen production or the reduction of carbon dioxide, nitrogen, and other compounds, addressing global energy and environmental challenges. In this review, we focus on the intricate details of the OER, particularly the role of manganese complexes. We consider the proposed mechanisms by which manganese complexes catalyze the OER, offering insights into the underlying chemistry. Following this, we explore model complexes that have been developed to emulate the OER and address the common issue of Mn complexes decomposing into manganese oxide during the process.

In Photosystem II (PS II) the D2 and D1 proteins provide binding sites for the primary (QA) and secondary (QB) plastoquinone electron acceptors, respectively. A non-heme iron is located between QA and QB that is coordinated by a bicarbonate ligand and two His residues from D1 (D1-His215 and D1-His272) and two His residues from D2 (D2-His214 and D2-His268). The symmetry of the quinone-Fe-acceptor complex extends to D1-Arg269, which has hydrogen bonds to D1-His272, and D2-Arg265 which has hydrogen bonds to D2-His268. We have examined the role of D2-Arg265 by creating the R265A and R265D mutants in the cyanobacterium Synechocystis sp. PCC 6803. Both mutants exhibited normal photoautotrophic growth, but showed a reduction in oxygen evolution in the presence of the PS II-specific electron acceptor 2,5-dimethyl-1,4-benzoquinone (DMBQ). Chlorophyll a fluorescence induction and decay kinetics were also inhibited in the presence of DMBQ and, in the presence of the native quinone, revealed slowed QA- to QB electron transfer, together with impaired exchange between the QB-binding site and the plastoquinone pool. Addition of formate further inhibited electron transfer, consistent with weakened bicarbonate binding in the mutants, and thermoluminescence measurements revealed a decreased redox gap between QA and QB. Additionally, both mutants displayed heightened sensitivity to high light. These findings demonstrate that D2-Arg265 is important for stability of the acceptor side, bicarbonate-dependent electron transfer, and an optimal QB-binding site. All of our results are also consistent with the architecture of the quinone-Fe-bicarbonate complex supporting photoprotection and regulatory roles that are unique to oxygenic photosynthesis.

Cytochrome b 559 (Cyt b 559 ) is a Photosystem II (PS II) protein formed by PsbE (the α‐subunit) and PsbF (the β‐subunit) that is essential for the biogenesis of the photosystem and may contribute to photoprotection via cyclic electron flow; however, the precise roles of Cyt b 559 and its molecular interactions with other proteins and cofactors remain unknown. We have introduced an Ala substitution in the α‐subunit of Cyt b 559 at PsbE:Phe10 in the cyanobacterium Synechocystis sp. PCC 6803. The conserved PsbE:Phe10 residue interacts with surrounding proteins and cofactors in the vicinity of the secondary plastoquinone electron acceptor Q B . Oxygen evolution in the F10A mutant underwent rapid inactivation in high light, which did not recover during darkness, but rapid recovery of PS II activity was induced by subsequent low‐light exposure. Lincomycin added before the high‐light treatment prevented the recovery of PS II activity under low light, whereas the addition of lincomycin after the high‐light treatment did not block recovery. These findings indicate exchanging PsbE:Phe10 for Ala resulted in the formation of a dark‐stable inactive PS II complex upon exposure to high light and that light‐induced protein synthesis during high‐light exposure conditioned the inactivated PS II for recovery via a process triggered by low light. Ala substitutions introduced at the neighboring PsbE:Pro9 and PsbE:Ser11 residues did not introduce the high‐light sensitive phenotype, indicating that the sensitivity to high light and the formation of the dark‐stable PS II complex were unique to the PsbE:F10A strain.

Water splitting by Photosystem II (PS II) in photosynthesis is catalyzed by a Mn4CaO5 oxygen-evolving complex (OEC). The reaction center D1 protein provides most of the ligands to the OEC but its complete assembly requires the association of the CP43 core antenna subunit which provides CP43:Glu341 as an essential ligand. In addition, CP43:Arg344 contributes key interactions to the OEC environment. These residues are in a hydrophilic loop (Loop E) that must gain access to the pocket housing the OEC in the membrane. We have investigated the role of the nearby and conserved CP43:Phe345 residue in the stabilization and function of the OEC. Substitutions removing the aromatic character of the side chain inactivated PS II activity by either preventing assembly (in the case of proline) or resulted in an inactive assembled photosystem (in the case of lysine). Substitution by alanine or by aromatic residues (histidine, tyrosine and tryptophan) supported photoautotrophic growth, although electron transfer between the OEC and the PS II reaction center was impaired. Additionally, the F345H mutant appeared to have fewer active PS II centers than control cells. Furthermore, the F345Y mutant, and to some extent the F345W strain, exhibited a redirection of light energy from Photosystem I to PS II as a potential response to correct for the reduced flow of electrons into the electron transport chain of these mutants. Collectively, these data show the hydrophobic character of CP43:Phe345 is required for the assembly and optimal activity of the OEC in PS II.

The chemical properties of the primary (QA) and secondary (QB) plastoquinone electron acceptors of Photosystem II (PS II) depend on their protein environments. The DE loop of the D2 protein (residues 222-262) contributes to the QA-binding site while the DE loop of the D1 protein (residues 233-266) contributes to the QB-binding environment. The roles of the invariant D2-Met246 and D2-Asn250 residues in the vicinity of the QA-binding site have been investigated in the cyanobacterium Synechocystis sp. PCC 6803 using mutants targeting both residues. The M246F strain was phenotypically similar to control cells; however, the M246A, N250A, and N250H strains had slowed photoautotrophic growth and were sensitive to high light and the addition of formate. In addition, the M246K and N250N strains were unable to assemble PS II. Chlorophyll a fluorescence measurements indicated electron transfer between QA and QB was modified in the M246A, N250A, and N250H strains, and the exchange of plastoquinol between the QB-binding site and the plastoquinone pool in the thylakoid membrane was impaired. Modified electron transfer in these mutants in the presence or absence of formate was restored by the addition of bicarbonate. In addition, thermoluminescence measurements showed a down shift in the redox midpoint potential of the QA/QA- couple in the N250A and N250H strains. These results demonstrate that Met246 and Asn250 play indispensable roles in the quinone-iron-acceptor complex, influencing both QA binding and the binding of the bicarbonate ligand to the non-heme iron that is located between QA and QB.

The excessive use of fossil fuels has led to significant environmental challenges, including global warming driven by carbon dioxide emissions and widespread air pollution. Essentially, focusing on sustainable and clean energy sources is necessary for the future of humanity and our planet. Through evolution, nature has solved this energy problem through the natural photosynthesis process. Manganese plays a crucial role in natural photosynthesis, specifically within the oxygen-evolving complex of photosystem II and therefore manganese has garnered significant interest for its potential use in catalytic, photocatalytic, and photoelectrochemical water oxidation, as well as in various other applications, due to its crucial role in natural photosynthesis. Therefore, This review focuses on the photocatalytic and photoelectrocatalytic properties of different manganese compounds and discusses various characterization techniques, with a special focus on electrochemical and photoelectrochemical methods used for assessing photoactive semiconductors. The primary goal of this text is to offer a comprehensive summary of the advancements in this area. Additionally, it sheds light on various approaches and strategies used in this field that could be applicable in related areas of interest. The review concludes with an outlook and final thoughts on the subject.

Photosystem II (PS II) is responsible for light-driven water splitting in oxygenic photosynthesis. The Psb27 protein, an assembly factor required for biogenesis of PS II, is found associated with hydrophilic regions of the CP43 core antenna protein in the thylakoid lumen. CP43 and the D1 reaction center protein provide ligands for the Mn4CaO5 oxygen-evolving complex (OEC). Release of Psb27 coincides with conformational changes that enable successful light-driven assembly of the OEC. This stage in biogenesis also requires changes to allow electron transfer between plastoquinone electron acceptors on the opposite side of the membrane. We have introduced charge-swap mutations to target the binding of Psb27 to CP43 during assembly. Here, we show that perturbation of the Psb27-CP43 interaction results in elevated fluorescence, indicating enhanced energy transfer to PS II in fully assembled complexes. In a Psb27:Arg78 to Glu mutant, D1:His252 spontaneously mutated to Gln. D1:His252 is in the DE loop that contributes to quinone binding and protonation. Mutations targeting D1:His252 produced mutants with elevated PS II-specific fluorescence that exceeded that observed in our Psb27 mutants and this was attenuated when the Psb27 charge-swap mutations were introduced into H252Q cells. Perturbation of Psb27 binding to CP43 therefore modified structural changes on the opposite side of the membrane resulting from mutation of D1:His252. The peripheral phycobilisome antenna is lost during thylakoid isolation and thylakoids from our mutants did not display the increased PS II-specific fluorescence. Hence Psb27 binding to CP43 during photoassembly of the OEC can modify phycobilisome-dependent energy transfer into PS II.

Enhancing crop photosynthesis through genetic engineering technologies offers numerous opportunities to increase plant productivity. Key approaches include optimizing light utilization, increasing cytochrome b6f complex levels, and improving carbon fixation. Modifications to Rubisco and the photosynthetic electron transport chain are central to these strategies. Introducing alternative photorespiratory pathways and enhancing carbonic anhydrase activity can further increase the internal CO2 concentration, thereby improving photosynthetic efficiency. The efficient translocation of photosynthetically produced sugars, which are managed by sucrose transporters, is also critical for plant growth. Additionally, incorporating genes from C4 plants, such as phosphoenolpyruvate carboxylase and NADP-malic enzymes, enhances the CO2 concentration around Rubisco, reducing photorespiration. Targeting microRNAs and transcription factors is vital for increasing photosynthesis and plant productivity, especially under stress conditions. This review highlights potential biological targets, the genetic modifications of which are aimed at improving photosynthesis and increasing plant productivity, thereby determining key areas for future research and development.

The Photosystem II water-plastoquinone oxidoreductase is a multi-subunit complex which catalyses the light-driven oxidation of water to molecular oxygen in oxygenic photosynthesis. The D1 reaction centre protein exists in multiple forms in cyanobacteria, including D1FR which is expressed under far-red light. We investigated the role of Phe184 that is found in the lumenal cd-loop of D1FR but is typically an isoleucine in other D1 isoforms. The I184F mutant in Synechocystis sp. PCC 6803 was similar to the control strain but accumulated a spontaneous mutation that introduced a Gln residue in place of His252 located on the opposite side of the thylakoid membrane. His252 participates in the protonation of the secondary plastoquinone electron acceptor QB. The I184F:H252Q double mutant exhibited reduced high-light-induced photodamage and an altered QB-binding site that impaired herbicide binding. Additionally, the H252Q mutant had a large increase in the variable fluorescence yield although the number of photochemically active PS II centres was unchanged. In the I184F:H252Q mutant the extent of the increased fluorescence yield decreased. Our data indicates substitution of Ile184 to Phe modulates PS II-specific variable fluorescence in cells with the His252 to Gln substitution by modifying the QB-binding site.

Indonesia is renowned as an agricultural powerhouse, ranking first globally in oil palm production. This prominence in agriculture leads to the consistent generation of agro-industrial waste, notably Palm Oil Mill Effluent (POME). Effectively addressing these waste concerns is important due to their adverse impacts on aquatic ecosystems and the nation’s health and economy. Anthropogenic wastewater with excessive phosphorus content can trigger eutrophication and toxic algal blooms, posing environmental risks and potentially precipitating a future clean water crisis. Thus, a comprehensive approach is necessary to restore the environment and biogeochemical cycles. Treatment efforts involving bioremediation agents aim to recycle organic and inorganic pollutants in the environment. Photosynthetic organisms like plants and microalgae serve as effective bioremediation agents, capable of absorbing excess phosphorus. They can utilize phosphate as an energy source to boost biomass. Integrating these bioremediation agents with bioengineering technology optimizes the treatment efficacy while simultaneously producing valuable biomass for products and bioenergy. This review article explores photosynthetic organisms’ multifunctional role as phosphorus bioremediation agents for wastewater treatment, minimizing environmental pollutant impacts, and providing biomass for fertilizers, polymers, bioplastics, and renewable energy. Furthermore, this study unveils opportunities for future technological advancements in this field.

AbstractThis is a tribute dedicated to Govindjee for his 92nd birthday. He is Professor Emeritus of Plant Biology, Biochemistry, and Biophysics at the University of Illinois in Urbana-Champaign (UIUC) since 1999. He is highly acclaimed as a pioneer and discoverer in photosynthesis research, having contributed to the concept of two pigment systems and two light reactions working in series in oxygenic photosynthesis (known as the Z-Scheme), and for his innovative research on the different processes involved in the light phase of photosynthesis. Moreover, Govindjee is much praised for his outstanding work as an editor, historian, and teacher of photosynthesis. Here, we celebrate his many achievements with an emphasis on his continuing scientific activity during twenty-five years of retirement. For this, we have analyzed all his publications between 1999 and 2024, grouped into six themes, as well as his work as an editor and a teacher.

The low-molecular-weight PsbM and PsbT proteins of Photosystem II (PS II) are both located at the monomer-monomer interface of the mature PS II dimer. Since the extrinsic proteins are associated with the final step of assembly of an active PS II monomer and, in the case of PsbO, are known to impact the stability of the PS II dimer, we have investigated the potential cooperativity between the PsbM and PsbT subunits and the PsbO, PsbU and PsbV extrinsic proteins. Blue-native polyacrylamide electrophoresis and western blotting detected stable PS II monomers in the ∆PsbM:∆PsbO and ∆PsbT:∆PsbO mutants that retained sufficient oxygen-evolving activity to support reduced photoautotrophic growth. In contrast, the ∆PsbM:∆PsbU and ∆PsbT:∆PsbU mutants assembled dimeric PS II at levels comparable to wild type and supported photoautotrophic growth at rates similar to those obtained with the corresponding ∆PsbM and ∆PsbT cells. Removal of PsbV was more detrimental than removal of PsbO. Only limited levels of dimeric PS II were observed in the ∆PsbM:∆PsbV mutant and the overall reduced level of assembled PS II in this mutant resulted in diminished rates of photoautotrophic growth and PS II activity below those obtained in the ∆PsbM:∆PsbO and ∆PsbT:∆PsbO strains. In addition, the ∆PsbT:∆PsbV mutant did not assemble active PS II centers although inactive monomers could be detected. The inability of the ∆PsbT:∆PsbV mutant to grow photoautotrophically, or to evolve oxygen, suggested a stable oxygen-evolving complex could not assemble in this mutant.

The 11th International Photosynthesis Conference on Hydrogen Energy Research and Sustainability 2023 was organized in honor of Robert Blankenship, Győző Garab, Michael Grätzel, Norman Hüner, and Gunnar Öquist, in Istanbul, Türkiye at Bahçeşehir University Future Campus from 03 to 09 July 2023. It was jointly supported by the International Society of Photosynthesis Research (ISPR) and the International Association for Hydrogen Energy (IAHE). In this article we provide brief details of the conference, its events, keynote speakers, and the scientific contribution of scientists honored at this conference. Further, we also describe the participation of young researchers, their talks, and their awards.

Photosystem II (PS II) assembly is a stepwise process involving preassembly complexes or modules focused around four core PS II proteins. The current model of PS II assembly in cyanobacteria is derived from studies involving the deletion of one or more of these core subunits. Such deletions may destabilize other PS II assembly intermediates, making constructing a clear picture of the intermediate events difficult. Information on plastoquinone exchange pathways operating within PS II is also unclear and relies heavily on computer-aided simulations. Deletion of PsbX in [S. Biswas, J.J. Eaton-Rye, Biochim. Biophys. Acta - Bioenerg. 1863 (2022) 148519] suggested modified QB binding in PS II lacking this subunit. This study has indicated the phenotype of the ∆PsbX mutant arose by disrupting a conserved hydrogen bond between PsbX and the D2 (PsbD) protein. We mutated two conserved arginine residues (D2:Arg24 and D2:Arg26) to further understand the observations made with the ∆PsbX mutant. Mutating Arg24 disrupted the interaction between PsbX and D2, replicating the high-light sensitivity and altered fluorescence decay kinetics observed in the ∆PsbX strain. The Arg26 residue, on the other hand, was more important for either PS II assembly or for stabilizing the fully assembled complex. The effects of mutating both arginine residues to alanine or aspartate were severe enough to render the corresponding double mutants non-photoautotrophic. Our study furthers our knowledge of the amino-acid interactions stabilizing plastoquinone-exchange pathways while providing a platform to study PS II assembly and repair without the actual deletion of any proteins.

In Photosystem II electrons from water splitting pass through a primary quinone electron acceptor (QA) to the secondary plastoquinone (QB). The D2 protein forms the QA-binding site and the D1 protein forms the Q(B)-binding site. A non-heme iron sits between QA and QB resulting in a quinone-Fe-acceptor complex that must be activated before assembly of the oxygen-evolving complex can occur. An extended loop (residues 223-266) between the fourth (helix D) and fifth (helix E) helices of the D1 protein activates forward electron transfer via a conformational change that stabilizes a bidentate bicarbonate ligand to the non-heme iron while simultaneously stabilizing the binding of QB. We show that positioning of D1:Phe265 to provide a hydrogen bond to the distal oxygen of QB is required for forward electron transfer. In addition, mutations targeting D1:Phe265, resulted in a 50 mV decrease in the QB/QB- midpoint potential.

Bicarbonate (HCO3-) binding regulates electron flow between the primary (QA) and secondary (QB) plastoquinone electron acceptors of Photosystem II (PS II). Lys264 of the D2 subunit of PS II contributes to a hydrogen-bond network that stabilizes HCO3- ligation to the non-heme iron in the QA-Fe-QB complex. Using the cyanobacterium Synechocystis sp. PCC 6803, alanine and glutamate were introduced to create the K264A and K264E mutants. Photoautotrophic growth was slowed in K264E cells but not in the K264A strain. Both mutants accumulated an unassembled CP43 precomplex as well as the CP43-lacking RC47 assembly intermediate, indicating weakened binding of the CP43 precomplex to RC47. Assembly was impeded more in K264E cells than in the K264A strain, but K264A cells were more susceptible to high-light-induced photodamage when assayed using PS II-specific electron acceptors. Furthermore, an impaired repair mechanism was observed in the K264A mutant in protein labeling experiments. Unexpectedly, unlike the K264A strain, the K264E mutant displayed inhibited oxygen evolution following high-light exposure when HCO3- was added to support whole chain electron transport. In both mutants, the decay of chlorophyll fluorescence was slowed, indicating impaired electron transfer between QA and QB. Furthermore, the fluorescence decay kinetics in the K264E strain were insensitive to addition of either formate or HCO3-, whereas HCO3--reversible formate-induced inhibition in the K264A mutant was observed. Exchange of plastoquinol with the membrane plastoquinone pool at the QB-binding site was also retarded in both mutants. Hence, D2-Lys264 possesses key roles in both assembly and activity of PS II.

The wavelengths of light harvested in oxygenic photosynthesis are ~400-700 nm. Some cyanobacteria respond to far-red light exposure via a process called far-red light photoacclimation which enables absorption of light at wavelengths >700 nm and its use to support photosynthesis. Far-red-light-induced changes include up-regulation of alternative copies of multiple proteins of Photosystem II (PS II). This includes an alternative copy of the D1 protein, D1FR . Here, we show that D1FR introduced into Synechocystis sp. PCC 6803 (hereafter Synechocystis 6803) can be incorporated into PS II centres that evolve oxygen at low rates but cannot support photoautotrophic growth. Using mutagenesis to modify the psbA2 gene of Synechocystis 6803, we modified residues in helices A, B, and C to be characteristic of D1FR residues. Modification of the Synechocystis 6803 helix A to resemble the D1FR helix A, with modifications in the region of the bound ß-carotene (CarD1 ) and the accessory chlorophyll, ChlZD1 , produced a strain with a similar phenotype to the D1FR strain. In contrast, the D1FR changes in helices B and C had minor impacts on photoautotrophy but impacted the function of PS II, possibly through a change in the equilibrium for electron sharing between the primary and secondary plastoquinone electron acceptors QA and QB in favour of QA - . The addition of combinations of residue changes in helix C indicates compensating effects may occur and highlight the need to experimentally determine the impact of multiple residue changes.