Julian J. Eaton-Rye

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.

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.

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.

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.

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.

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.