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New and enhanced functions were potentially imparted to the plant organelles after interaction with nanoparticles. In this study, we found that ∼ 44% and ∼ 29% of the accumulated graphene in the rice leaves passively transported to the chloroplasts and thylakoid, respectively, significantly enhanced the fluorescence intensity of chloroplasts, and promoted about 2.4 times higher adenosine triphosphate production than that of controls. The enhancement of graphene on the photophosphorylation was ascribed to two reasons: One is that graphene facilitates the electron transfer process of photosystem II in thylakoid, and the other is that graphene protects the photosystem II against photo-bleaching by acting as a scavenger of reactive oxygen species. Overall, our work here confirmed that graphene translocating in the thylakoid promoted the photosynthetic activity of chloroplast in vivo and in vitro , providing new opportunities for designing biomimetic materials to enhance the solar energy conversion systems, especially for repairing or increasing the photosynthesis activity of the plants grown under stress environment.

Photosynthetic linear electron flow (LEF) produces ATP and NADPH, while cyclic electron flow (CEF) exclusively drives photophosphorylation to supply extra ATP. The fine-tuning of linear and cyclic electron transport levels allows photosynthetic organisms to balance light energy absorption with cellular energy requirements under constantly changing light conditions. As LEF and CEF share many electron transfer components, a key question is how the same individual structural units contribute to these two different functional modes. Here, we report the structural identification of a photosystem I (PSI)–light harvesting complex I (LHCI)–cytochrome (cyt) b₆f supercomplex isolated from the unicellular alga Chlamydomonas reinhardtii under anaerobic conditions, which induces CEF. This provides strong evidence for the model that enhanced CEF is induced by the formation of CEF supercomplexes, when stromal electron carriers are reduced, to generate additional ATP. The additional identification of PSI–LHCI–LHCII complexes is consistent with recent findings that both CEF enhancement and state transitions are triggered by similar conditions, but can occur independently from each other. Single molecule fluorescence correlation spectroscopy indicates a physical association between cyt b₆f and fluorescent chlorophyll containing PSI–LHCI supercomplexes. Single particle analysis identified top-view projections of the corresponding PSI–LHCI–cyt b₆f supercomplex. Based on molecular modeling and mass spectrometry analyses, we propose a model in which dissociation of LHCA2 and LHCA9 from PSI supports the formation of this CEF supercomplex. This is supported by the finding that a Δlhca2 knockout mutant has constitutively enhanced CEF.

The construction of energetically autonomous artificial protocells is one of the most ambitious goals in bottom-up synthetic biology. Here, we show an efficient manner to build adenosine 5′- triphosphate (ATP) synthesizing hybrid multicompartment protocells. Bacterial chromatophores from Rhodobacter sphaeroides accomplish the photophosphorylation of adenosine 5′-diphosphate (ADP) to ATP, functioning as nanosized photosynthetic organellae when encapsulated inside artificial giant phospholipid vesicles (ATP production rate up to ∼100 ATP·s−1 per ATP synthase). The chromatophore morphology and the orientation of the photophosphorylation proteins were characterized by cryo-electron microscopy (cryo-EM) and time-resolved spectroscopy. The freshly synthesized ATP has been employed for sustaining the transcription of a DNA gene, following the RNA biosynthesis inside individual vesicles by confocal microscopy. The hybrid multicompartment approach here proposed is very promising for the construction of full-fledged artificial protocells because it relies on easy-to-obtain and ready-to-use chromatophores, paving the way for artificial simplified-autotroph protocells (ASAPs).

The Calvin–Benson cycle and the photorespiratory pathway form the photosynthetic–photorespiratory supercycle that is responsible for nearly all biological CO₂ fixation on Earth. In essence, supplementation with the photorespiratory pathway is necessary because the CO₂-fixing enzyme of the Calvin–Benson cycle, ribulose 1,5-bisphosphate carboxylase (Rubisco), catalyses several side reactions including the oxygenation of ribulose 1,5-bisphosphate, which produces the noxious metabolite phosphoglycolate. The photorespiratory pathway recycles the phosphoglycolate to 3-phosphoglycerate and in this way allows the Calvin–Benson cycle to operate in the presence of molecular oxygen generated by oxygenic photosynthesis. While the carbon flow through the individual and combined subprocesses is well known, information on their regulatory interaction is very limited. Regulatory feedback from the photorespiratory pathway to the Calvin–Benson cycle can be presumed from numerous inhibitor experiments and was demonstrated in recent studies with transgenic plants. This complexity illustrates that we are not yet ready to rationally engineer photosynthesis by altering photorespiration since despite massive understanding of the core photorespiratory pathway our understanding of its interaction with other pathways and processes remains fragmentary.

I present here a personal reminiscence of the life and research of Frederick Robert (Bob) Whatley (January 26, 1924-November 14, 2020). He was responsible for showing that chloroplasts are complete units for oxygenic photosynthesis and that photophosphorylation is what is common between anoxygenic and oxygenic photosynthesis. He had an innovative nature and exploited many biophysical and biochemical techniques to understand, in depth, the regulatory nature of photosynthesis. Bob Whatley was a self-sufficient, thorough, quiet, and confident scientist, but he was self-effacing and never ever blew his own horn. My presentation is mingled a bit, at places, with my own thoughts - to give it a personal touch.

Nitrogenase is an ATP-requiring enzyme capable of carrying out multielectron reductions of inert molecules. A purified remodeled nitrogenase containing two amino acid substitutions near the site of its FeMo cofactor was recently described as having the capacity to reduce carbon dioxide (CO₂) to methane (CH₄). Here, we developed the anoxygenic phototroph, Rhodopseudomonas palustris, as a biocatalyst capable of light-driven CO₂ reduction to CH₄ in vivo using this remodeled nitrogenase. Conversion of CO₂ to CH₄ by R. palustris required constitutive expression of nitrogenase, which was achieved by using a variant of the transcription factor NifA that is able to activate expression of nitrogenase under all growth conditions. Also, light was required for generation of ATP by cyclic photophosphorylation. CH₄ production by R. palustris could be controlled by manipulating the distribution of electrons and energy available to nitrogenase. This work shows the feasibility of using microbes to generate hydrocarbons from CO₂ in one enzymatic step using light energy.

Marine cyanobacteria are responsible for ~25% of the fixed carbon that enters the ocean biosphere. It is thought that abundant co-occurring viruses play an important role in regulating population dynamics of cyanobacteria and thus the cycling of carbon in the oceans. Despite this, little is known about how viral infections ‘play-out’ in the environment, particularly whether infections are resource or energy limited. Photoautotrophic organisms represent an ideal model to test this since available energy is modulated by the incoming light intensity through photophosphorylation. Therefore, we exploited phototrophy of the environmentally relevant marine cyanobacterium Synechococcus and monitored growth of a cyanobacterial virus (cyanophage). We found that light intensity has a marked effect on cyanophage infection dynamics, but that this is not manifest by a change in DNA synthesis. Instead, cyanophage development appears energy limited for the synthesis of proteins required during late infection. We posit that acquisition of auxiliary metabolic genes (AMGs) involved in light-dependent photosynthetic reactions acts to overcome this limitation. We show that cyanophages actively modulate expression of these AMGs in response to light intensity and provide evidence that such regulation may be facilitated by a novel mechanism involving light-dependent splicing of a group I intron in a photosynthetic AMG. Altogether, our data offers a mechanistic link between diurnal changes in irradiance and observed community level responses in metabolism, i.e., through an irradiance-dependent, viral-induced release of dissolved organic matter (DOM).

After a brief prologue on Otto Kandler’s life, we describe briefly his pioneering work on photosynthesis (photophosphorylation and the carbon cycle) and his key participation in the discovery of the concept of three forms of life (Archaea, Prokarya, and Eukarya). With Otto Kandler’s passing, both the international photosynthesis and microbiology communities have lost an internationally unique, eminent, and respected researcher and teacher who exhibited a rare vibrancy and style.

The present study was conducted to examine the effects of increasing concentrations of chromium (Cr⁶⁺) (0, 25, 50, 100, and 200 μmol) on rice (Oryza sativa L.) morphological traits, photosynthesis performance, and the activities of antioxidative enzymes. In addition, the ultrastructure of chloroplasts in the leaves of hydroponically cultivated rice (O. sativa L.) seedlings was analyzed. Plant fresh and dry weights, height, root length, and photosynthetic pigments were decreased by Cr-induced toxicity (200 μM), and the growth of rice seedlings was starkly inhibited compared with that of the control. In addition, the decreased maximum quantum yield of primary photochemistry (Fv/Fm) might be ascribed to the decreased the number of active photosystem II reaction centers. These results were confirmed by inhibited photophosphorylation, reduced ATP content and its coupling factor Ca²⁺–ATPase, and decreased Mg²⁺–ATPase activities. Furthermore, overtly increased activities of antioxidative enzymes were observed under Cr⁶⁺ toxicity. Malondialdehyde and the generation rates of superoxide (O2̄) also increased with Cr⁶⁺ concentration, while hydrogen peroxide content first increased at a low Cr⁶⁺ concentration of 25 μM and then decreased. Moreover, transmission electron microscopy showed that Cr⁶⁺ exposure resulted in significant chloroplast damage. Taken together, these findings indicate that high Cr⁶⁺concentrations stimulate the production of toxic reactive oxygen species and promote lipid peroxidation in plants, causing severe damage to cell membranes, degradation of photosynthetic pigments, and inhibition of photosynthesis.

Microorganisms are believed to participate in the biotic process of deep-sea ferromanganese nodule formation [Mn(II) oxidation]. Despite the multitude of studies and reviews focusing on the details of Mn(II) oxidation catalyzed by diverse heterotrophs, the mechanistic roles of manganese chemolithotrophs from ferromanganese nodules remain unclear. We demonstrate that strain Georhizobium sp. MAB10 can utilize Mn(II)-derived electrons for photoautotrophic growth, with concomitant generation of dark β-MnO 2 type Mn oxides under near-infrared light condition. This study uses genomic and biochemical assays to explore the genetic basis of Mn(II) oxidation-coupled anoxygenic photoautotrophy. The comprehensive analyses of respiration and carbon and nitrogen metabolism further elucidated the high ecophysiological flexibility of strain MAB10 in deep-sea habits. These findings expand our understanding of the role of chemolithotrophs in deep-sea ferromanganese nodule formation and justify further investigations into the molecular basis for Mn(II) oxidation-coupled anoxygenic photoautotrophy.