Chloroplast ATP synthase: From structure to engineering

Evaluating the influence of phosphorus supply on photosynthetic and agronomic performance of two breeding lines of common bean grown under acidic soil and high temperature stress

High temperature stress has a significant effect on the physiological response of the bean crop (Phaseolus vulgaris L.) and the supply of phosphorus (P) can influence photosynthetic performance, mobilization of photoassimilates and alleviate heat stress. The objective of this study was to evaluate the influence of increasing P supply on the response of the photosynthetic apparatus of two breeding lines of common bean grown in acidic soil under high temperature stress conditions in a screenhouse. A completely randomized block design with factorial arrangement was used: i. five levels of P supply (P0, P15, P30 and P45 kg ha-1; and P supplied through organic matter [PSOM at P25]), and ii. two bean lines (BFS 10, SEF 10) with a total of ten treatments and four replications. During the study, the ambient temperature rose to 37°C and 29°C during the day and night, respectively, a high temperature stress condition that significantly affected the functioning of the photosynthetic apparatus of the two bean lines evaluated. Under these growing conditions, the bean lines adjusted in canopy temperature, reducing leaf temperature by 3.6 to 4.0°C compared to ambient temperature, a process performed more efficiently by SEF 10 compared to BFS 10. Increased P supply improved electron transport chain function, ATP production, PSII photochemical efficiency (Fv/Fm), the fraction of energy devoted to the photosynthesis process (ΦII); and reduced the amount of energy in the form of heat (ΦNPQ) as the need for heat dissipation manifested through leaf temperature difference (LTD). These adjustments to photosynthetic apparatus translated into superior agronomic performance through greater partitioning of dry matter into grain yield (GY) as revealed by partitioning indices such as pod partitioning index (PPI), pod harvest index (PHI) and harvest index (HI), and yield components including pod number per area (PNA) and seed number per area (SNA). Increased P supply increased leaf P concentration and alleviated the effects of high temperature on the functioning of the photosynthetic apparatus in both common bean lines (BFS 10 and SEF 10); and accumulation of sugars in pods and seeds facilitated improved seed yield. These two bean lines can serve as parents in bean breeding programs that aim to combine low P tolerance with high temperature tolerance in acid soil regions of the tropics.

Structure, regulation and assembly of the photosynthetic electron transport chain

The electron transfer chain of chloroplast thylakoid membranes uses solar energy to split water into electrons and protons, creating energetic gradients that drive the formation of photosynthetic fuel in the form of NADPH and ATP. These metabolites are then used to power the fixation of carbon dioxide into biomass through the Calvin-Benson-Bassham cycle in the chloroplast stroma. Recent advances in molecular genetics, structural biology and spectroscopy have provided an unprecedented understanding of the molecular events involved in photosynthetic electron transfer from photon capture to ATP production. Specifically, we have gained insights into the assembly of the photosynthetic complexes into larger supercomplexes, thylakoid membrane organization and the mechanisms underpinning efficient light harvesting, photoprotection and oxygen evolution. In this Review, I focus on the angiosperm plant thylakoid system, outlining our current knowledge on the structure, function, regulation and assembly of each component of the photosynthetic chain. I explain how solar energy is harvested and converted into chemical energy by the photosynthetic electron transfer chain, how its components are integrated into a complex membrane macrostructure and how this organization contributes to regulation and photoprotection.

Integrative Analysis of Transcriptomic and Metabolomic Profiles Uncovers the Mechanism of Color Variation in the Tea Plant Callus

Tea plants (Camellia sinensis) are among the world's most significant economic tree species. Tissue culture serves as a crucial method in commercial breeding by facilitating the rapid propagation of valuable genotypes and the generation of disease-free clones. However, callus browning represents a prevalent challenge in tea plant tissue culture, and may adversely affect explant growth and development. Our research demonstrates that although anti-browning agents can effectively suppress browning, they induce distinct color changes in the callus. These color variations could significantly influence callus induction and subsequent growth patterns. In this study, callus tissues from C. sinensis var. Assamica cv. Mengku were employed as experimental materials and treated with three commonly used anti-browning agents: ascorbic acid (VC), activated carbon (AC), and polyvinylpyrrolidone (PVP). The results demonstrated that while these three reagents effectively inhibited browning, they also induced distinct color changes in the explants, which appeared red, green, and white, respectively. Furthermore, this study investigated the molecular mechanisms underlying callus color changes using transcriptomic and metabolomic approaches. Based on transcriptome analysis, it was revealed that photosynthesis and flavonoid biosynthesis pathways were significantly enriched. Metabolome analysis identified 14 phenolic acids, which exhibited significant variation in accumulation across calluses of different colors. The differential expression of genes involved in flavonoid biosynthesis pathways, coupled with the distinct accumulation patterns of metabolites, can effectively alleviate photooxidative damage and enhance the resistance of callus to browning. AC activates the photosynthesis of callus by regulating carbon source allocation and upregulating the expression of key genes in the psa, psb, and pet families within the photosynthetic system. This process promotes chlorophyll biosynthesis, thereby enabling the callus to grow green, while VC activates the expression of key genes such as CHS, F3H, C4H, CYP75B1, and ANR in the flavonoid pathway, which are involved in the regulation of pigment synthesis in red callus. This study elucidated the molecular mechanisms underlying the effects of anti-browning agents on color variations in C. sinensis callus, thereby providing a robust theoretical foundation for optimization, the establishment of tea plant tissue culture systems, and enhancing cultivar quality.

Structure of ATP synthase from an early photosynthetic bacterium Chloroflexus aurantiacus

F-type ATP synthase (F1FO) catalyzes proton motive force-driven ATP synthesis in mitochondria, chloroplasts, and bacteria. Different from the mitochondrial and bacterial enzymes, F1FO from photosynthetic organisms have evolved diverse structural and mechanistic details to adapt to the light-dependent reactions. Although complete structure of chloroplast F1FO has been reported, no high-resolution structure of an F1FO from photosynthetic bacteria has been available. Here, we report cryo-EM structures of an intact and functionally competent F1FO from Chloroflexus aurantiacus (CaF1FO), a filamentous anoxygenic phototrophic bacterium from the earliest branch of photosynthetic organisms. The structures of CaF1FO in its ADP-free and ADP-bound forms for three rotational states reveal a previously unrecognized architecture of ATP synthases. A pair of peripheral stalks connect to the CaF1 head through a dimer of δ-subunits, and associate with two membrane-embedded a-subunits that are asymmetrically positioned outside and clamp CaFO's c10-ring. The two a-subunits constitute two proton inlets on the periplasmic side and two proton outlets on the cytoplasmic side, endowing CaF1FO with unique proton translocation pathways that allow more protons being translocated relative to single a-subunit F1FO. Our findings deepen understanding of the architecture and proton translocation mechanisms of F1FO synthases and suggest innovative strategies for modulating their activities by altering the number of a-subunit.

ATP Synthase Members of Chloroplasts and Mitochondria in Rubber Trees (Hevea brasiliensis) Response to Plant Hormones

ATP synthase is a key enzyme in photophosphorylation in photosynthesis and oxidative phosphorylation in respiration, which can catalyze the synthesis of ATP and supply energy to organisms. ATP synthase has been well studied in many animal species but has been poorly characterized in plants. This research identified forty ATP synthase family members in the rubber tree, and the phylogenetic relationship, gene structure, cis-elements, and expression pattern were analyzed. These results indicated that the ATP synthase of mitochondria was divided into three subgroups and the ATP synthase of chloroplast was divided into two subgroups, respectively. ATP synthase in the same subgroup shared a similar gene structure. Evolutionary relationships were consistent with the introns and exons domains, which were highly conserved patterns. A large number of cis elements related to light, phytohormones and stress resistance were present in the promoters of ATP synthase genes in rubber trees, of which the light signal accounts for the most. Transcriptome and qRT-PCR analysis showed that HbATP synthases responded to cold stress and hormone stimulation, and the response to ethylene was most significant. HbMATPR3 was strongly induced by ethylene and salicylic acid, reaching 122-fold and 17-fold, respectively. HbMATP7-1 was 41 times higher than the control after induction by jasmonic acid. These results laid a foundation for further studies on the function of ATP synthase, especially in plant hormone signaling in rubber trees.

Structure, Regulation, and Significance of Cyanobacterial and Chloroplast Adenosine Triphosphate Synthase in the Adaptability of Oxygenic Photosynthetic Organisms

In cyanobacteria and chloroplasts (in algae and plants), ATP synthase plays a pivotal role as a photosynthetic membrane complex responsible for producing ATP from adenosine diphosphate and inorganic phosphate, utilizing a proton motive force gradient induced by photosynthesis. These two ATP synthases exhibit similarities in gene organization, amino acid sequences of subunits, structure, and functional mechanisms, suggesting that cyanobacterial ATP synthase is probably the evolutionary precursor to chloroplast ATP synthase. In this review, we explore the precise synthesis and assembly of ATP synthase subunits to address the uneven stoichiometry within the complex during transcription, translation, and assembly processes. We also compare the regulatory strategies governing ATP synthase activity to meet varying energy demands in cyanobacteria and chloroplasts amid fluctuating natural environments. Furthermore, we delve into the role of ATP synthase in stress tolerance and photosynthetic carbon fixation efficiency in oxygenic photosynthetic organisms (OPsOs), along with the current researches on modifying ATP synthase to enhance carbon fixation efficiency under stress conditions. This review aims to offer theoretical insights and serve as a reference for understanding the functional mechanisms of ATP synthase, sparking innovative ideas for enhancing photosynthetic carbon fixation efficiency by utilizing ATP synthase as an effective module in OPsOs.