Sodium aescinate induces renal cell ferroptosis through the ATF4/CTH/SQOR axis.

Water loss is a major challenge for photosynthetic organisms. Most are prone to drought stress and only few can tolerate full desiccation. Here, we investigated regulation of photosynthetic electron flow during dehydration and rehydration in Haematococcus lacustris, a desiccation tolerant green alga. During dehydration, non-photochemical quenching (NPQ) increased for dissipating excess light energy, while light-use efficiency of photosystems II (PSII) and I (PSI) decreased. The reaction centre of PSI (P700) became electron-limited at its donor side, helping form photoprotective P700+. Inhibiting alternative oxidases with octyl gallate delayed chlorophyll fluorescence quenching, indicating that plastid terminal oxidases (PTOX) supported formation of NPQ during desiccation. Reduction rates of P700+ during a saturating pulse were slower if cells dehydrated slower, showing that photoprotection was upregulated during desiccation acclimation. During rehydration, octyl gallate and diphenyleneiodonium (DPI), a flavoenzyme inhibitor, slowed oxidation of P700 under actinic light, indicating PTOX and flavodiiron proteins (FLV) were involved in maintaining P700+. A similar response occurred with the protonophore nigericin. We conclude that beyond preventing over-reduction of the electron transport chain, PTOX and FLV facilitated thylakoid luminal acidification under low water stress, protecting photosystems via NPQ, photosynthetic control and P700+ formation.

Aerobic respiration underpins animal performance, yet the mitochondrial electron transport system is often treated as a single, vertebrate-centric blueprint. This view overlooks alternative oxidase (AOX), an enzyme that allows electrons to bypass complexes III and IV, partially uncoupling oxidative phosphorylation. Although AOX is well-studied in plants for its role in stress-tolerance, its presence in animals was recognized only recently, leaving its contribution to metabolic flexibility underappreciated. Here, we used an emerging ecological-evolutionary-developmental biology (eco-evo-devo) and biomedical model, Nematostella vectensis, to test the hypothesis that AOX supports stress tolerance by bypassing complex IV (cytochrome c oxidase; COX) during hydrogen sulphide (H2S) exposure and by mitigating oxidative damage under hypoxia and heat stress via reduced reactive oxygen species (ROS) production. We found that anemones upregulated AOX protein expression after H2S exposure and exhibited cyanide-resistant respiration, consistent with continued electron flow despite COX inhibition. Behavioural assays showed that AOX inhibition increased sensitivity to H2S, declining oxygen and heat, while biochemical assays revealed that AOX inhibition led to elevated lipid peroxidation and protein carbonylation with hypoxia and heat exposure. Together, these results establish AOX as a critical yet overlooked mechanism of metabolic flexibility that buffers aerobic metabolism against multiple stressors, challenging textbook portrayals of conserved mitochondrial function and offering new perspectives on how animal persist in a rapidly changing world.

In higher plants, the L-galactose pathway is the main pathway for the biosynthesis of vitamin C (ascorbate, Asc), the final step of which is connected with the functioning of the mitochondrial electron transport chain (ETC). In addition to the main cytochrome pathway, plant ETC includes an alternative pathway (AP) via alternative terminal oxidase (AOX). The engagement of AOX promotes Asc synthesis, and it is hypothesized that AOX suppression under conditions of Asc deficiency may reduce plant viability. The aim of this work was to examine the consequences of simultaneously knocking out two genes in Arabidopsis thaliana: AOX1a, the most stress-inducible AOX gene, and VTC2, encoding a key enzyme of the L-galactose pathway of Asc synthesis. Two lines of A. thaliana with T-DNA insertions in the target genes were crossed to generate hybrid lines. Seed characteristics of the first (F1) and second (F2) generations were analyzed. F1 seeds were larger than those of parent lines, possibly due to heterosis. In the F2 generation, self-pollination of F1 plants resulted in seeds with significant size variation, including a group of small seeds with degenerative morphological abnormalities. Most of small seeds failed to germinate or died at the seedling stage. PCR genotyping of these seeds revealed the absence of native AOX1a and VTC2 indicating a lethal mutation caused by simultaneous knockout of both genes. One likely genetic cause is the interaction of mutations in non-allelic genes. At the physiological level, irreversible respiratory damage may occur, possibly including the impact of a cryptic mutation in the vtc2 line. Further studies are necessary to confirm these hypotheses. In general, the results obtained indicate the vital co-functioning of the AP and the L-galactose pathway of Asc biosynthesis and may be useful for the development of genetically engineered techniques for the control of vitamin C synthesis in plants.

The history of Earth's atmospheric oxygen is a cornerstone of evolutionary biology. While unequivocal evidence for an increase in atmospheric O2 marks the Great Oxidation Event (GOE) roughly 2.4 billion years ago, evidence underlying proposals for pre-GOE O2 accumulation is debated. Here we have investigated the distribution of genes for oxygen reductases, the enzymes that consume O2 in respiratory chains, across independently generated molecular timescales of prokaryotic evolution. The data indicate that cytochrome bd-oxidases, heme-copper oxidases and alternative oxidases arose in the wake of the GOE ca. 2.4 billion years ago, after which the genes were subjected to abundant lateral gene transfer, a reflection of their utility in redox balance and membrane bioenergetics. The data lead us to propose a straightforward four-stage model for O2 accumulation surrounding the GOE: (i) Negligible O2 existed prior to the GOE. (ii) Cyanobacterial O2 production started at the GOE, yet was capped at 2% [v/v] atmospheric O2, the threshold at which cyanobacterial nitrogenase is inhibited by O2. (iii) Production of 0.02atm of O2 (2% [v/v]) at the GOE buried roughly the entire atmospheric CO2 inventory, causing sudden enrichment of 13C in dissolved inorganic carbon (the Lomagundi 13C anomaly), through RuBisCO isotope discrimination, without atmospheric O2 exceeding 2% [v/v]. (iv) High atmospheric 12C at the end of the Lomagundi excursion marks the origin of oxygen reductases, their rapid spread via function in respiratory CO2 liberation, and the onset of equilibrium between photosynthetic O2 production and respiratory O2 consumption at 2% atmospheric O2.

Mitochondrial metabolism regulates the immunogenic responsiveness of dendritic cells.

The mitochondrial FoF1-ATP synthase is a reversible nanomachine that normally produces ATP via oxidative phosphorylation but under stress conditions it can reverse to maintain the mitochondrial membrane potential at the expense of ATP, a process regulated by the conserved inhibitory factor 1 (IF1). We show that ATP synthase reversal also occurs during in vitro-induced differentiation of the unicellular parasite Trypanosoma brucei, partially mirroring events in the tsetse fly. Differentiation of insect forms is marked by increased expression of alternative oxidase and reduced levels of trypanosomal IF1 (TbIF1), changes that may promote ATP synthase reversal. Parasites lacking TbIF1 efficiently progressed to the mammalian-infective form, coinciding with increased ATP synthase reversal, a higher ADP/ATP ratio, elevated phosphorylation of AMP-activated protein kinase (AMPK), enhanced proline-supported respiration, and increased mitochondrial and cellular reactive oxygen species (ROS). In contrast, inducible TbIF1 overexpression diminished these hallmarks and locked parasites in the initial insect stage. Our findings reveal that TbIF1 downregulation enables life cycle progression and underscore a regulatory role for the ATP synthase-IF1 axis.

Salinity (NaCl) and wheat curl mite infestation profoundly alter nitric oxide (NO) metabolism in barley, with NaCl dose-dependent responses indicating that nitrogen metabolism is fine-tuned through NO-signaling pathways. Nitric oxide (NO) serves as a multifaceted regulator in plants' responses to environmental stress, acting as both a signaling molecule and a protective agent, while also exhibiting potential harmful effects. Our study investigated NO metabolism in barley (Hordeum vulgare L.) plants under salinity (50mM and 100mM NaCl) and wheat curl mite (WCM) infestation, exposed to either single stressor or both stressors simultaneously. To accomplish our objectives, we adopted an integrated approach that combines biochemical, molecular, and microscopic techniques. We found that these stressors influence the production of NO and its subcellular distribution. Both nitrate reductase (NR) and non-enzymatic processes contribute to the production of NO. Under combined stress (50mM NaCl + WCM), NO molecules were detected in the cytoplasm, vacuoles, and chloroplasts, along with elevated NR activity. NO fluorescence in cell walls suggests its role in the apoplastic response of barley under dual stress, which induced a probable synergistic effect caused by salinity and WCM effectors. Upregulation of alternative oxidase AOX and phytoglobin Pgb gene expression, along with decreased activity of S-nitrosoglutathione reductase (GSNOR), in all combinations indicates sophisticated regulation of NO metabolism through transcriptional and enzymatic mechanisms. The accumulation of 3-nitrotyrosines under high salinity and dual stress points to increased nitro-oxidative stress. Moreover, an inhibitory effect of a 100mM NaCl salinity dose was demonstrated on WCM reproduction. Altogether, these findings provide a mechanistic framework for exploiting NO-related pathways as potential targets in breeding or biotechnological strategies aimed at improving barley tolerance to combined abiotic-biotic stress conditions, while simultaneously limiting pest performance under salinity.

Dehydration intensity modulates mitochondrial ultrastructure and redox homeostasis in the extremotolerant desert moss Syntrichiacaninervis.

The coordination of photosynthesis and respiration is central to cellular energy balance, yet in algae, this relationship exhibits exceptional diversity. Shaped by successive endosymbioses, algal lineages represent natural experiments in merging two energy systems of distinct bacterial ancestry: the chloroplast and the mitochondrion. Their structural proximity, shared redox pathways, and dual-targeted proteins enable dynamic communication between photosynthetic and respiratory metabolism. Recent imaging and multi-omics studies reveal that this interaction is highly responsive to environmental variables such as light intensity, nutrient availability, and oxidative stress. In diatoms, mitochondria envelop the plastid to exchange ATP and reducing power, whereas in green algae and euglenoids, malate/oxaloacetate shuttles, alternative oxidases, and cyclic electron flow collectively stabilize chloroplast redox states. This functional coupling optimizes CO2 fixation and photoprotection under stress and underlies the metabolic flexibility of mixotrophic species such as Euglena gracilis. This review synthesizes the current understanding of mitochondria-chloroplast integration in algae from evolutionary, structural, and mechanistic perspectives, highlighting photosynthesis-respiration coordination as a unifying physiological principle. By elucidating how inter-organelle networks sustain carbon assimilation and redox homeostasis, these insights advance our understanding of algal productivity and resilience and inform strategies for improving energy efficiency in photosynthetic systems.

The critical role of autophagy in mitigating acid stress-induced hypersusceptibility response in Arabidopsis thaliana.

COX6B1 is a nuclear-encoded subunit of the human mitochondrial cytochrome c oxidase (cIV) located in its intermembrane space-facing region. The relevance of COX6B1 in mitochondrial physiopathology was highlighted by the missense pathogenic variants associated with cIV deficiency. Despite the assigned COX6B1 role as a late incorporation subunit, the COX6B1 human cell line KO exhibited a total loss of cIV. To get a deeper insight into the mechanisms driving the lack of cIV assembly or destabilization in the absence of COX6B1, we used the COX6B1 KO cell background to express alternative oxidase and COX6B1 pathogenic variants. These analyses uncovered that the COX6B1 subunit is indispensable for redox-sensitive early cIV assembly steps, besides its contribution to the stabilization of cIV in the late assembly stages. In addition, we have evidenced the incorporation of partially assembled cIV modules directly into supercomplex structures, supporting the "cooperative assembly" model for respiratory chain biogenesis.

The study aimed to investigate the effect of overexpression of alternative mitochondrial enzymes such as yeast NADH dehydrogenase I (NDI1) and alternative oxidase (AOX) on the metabolism, oxidative stress and feeding behavior of the fruit fly Drosophila melanogaster. Experimental flies with expression of NDI1 or AOX were generated using genetic crosses based on the GAL4-UAS system. Female flies with NDI1 expression showed increased food consumption, markers of oxidative stress (elevated carbonyl protein content), and increased activity of the detoxification enzyme glutathione-S-transferase, along with decreased activity of key metabolic enzymes, including dehydrogenases of isocitrate, lactate, and glucose-6-phosphate. In contrast, AOX-expressing flies had reduced lactate dehydrogenase activity, decreased levels of lipid peroxides, and increased glutathione reductase activity. Lower free glucose levels with elevated glycogen stores were found in AOX-expressing female flies. The results suggest that the alternative electron transport chain may alter energy and redox metabolism. In particular, NDI1 expression could increase energy demand and induce compensatory hyperphagia. In contrast, AOX might bypass key steps of proton gradient generation, potentially reducing superoxide production.

Mitochondrial protein import is indispensable for organelle biogenesis and function, and is powered by the evolutionarily conserved presequence translocase-associated motor (PAM) complex. In Arabidopsis thaliana, three paralogs: PAM18-1, PAM18-2, and PAM18-3 encode J-domain proteins homologous to yeast PAM18, which stimulates the ATPase activity of mitochondrial HSP70 (mtHSP70) during protein translocation. Here, we identify PAM18-3 as the most highly and ubiquitously expressed paralog and demonstrate its critical role in mitochondrial function and plant development. Genetic disruption of PAM18-3 caused severe vegetative and reproductive defects, including reduced root length, smaller rosette size with fewer leaves, decreased plant height, shorter siliques, reduced seed set, and increased seed abortion. These phenotypes were fully rescued in complemented lines expressing PAM18-3. Ultrastructural analyses revealed profound mitochondrial abnormalities in mutants, whereas chloroplast architecture remained unaffected. Functional assays showed reduced mitochondrial membrane potential and altered respiratory flux with a compensatory induction of the alternative oxidase (AOX) pathway. Transcript profiling revealed upregulation of AOX genes and multiple components of the mitochondrial TIM23 import apparatus and associated chaperones. Import assays demonstrated reduced mitochondrial accumulation of canonical TIM23 substrates, including IDH, ATPβ, and SHMT1, confirming a defect in matrix protein translocation. Consistently, pam18-3 mutants accumulated elevated reactive oxygen species (ROS) and exhibited strong induction of mitochondrial dysfunction stimulon (MDS) genes, including key transcription factors mediating retrograde signaling. Together, our findings establish PAM18-3 as a central component of the mitochondrial protein import machinery, supporting plant growth and development in A. thaliana.

Ethylene, as a crucial plant hormone, plays a significant role in regulating plant growth, development, and stress responses. In this study, we developed a novel two-photon fluorescent probe, ETP, based on a naphthalene fluorophore, to detect ethylene fluctuations in plants with high sensitivity and specificity. Experimental results demonstrated that ETP could efficiently penetrate plant cells, exhibiting a marked increase in the fluorescence intensity corresponding to rising ethylene levels. Given that AOX1A (Alternative Oxidase 1A), a key component of the ethylene signaling pathway, enhances ethylene sensitivity, we applied ETP for ethylene imaging in both wild-type and AOX1A transgenic Arabidopsis (AOX1A overexpressor). Following ACC treatment, the mutant plants exhibited significantly higher ethylene production than the wild type, and ETP successfully visualized these differences. Furthermore, fluorescence lifetime imaging experiments confirmed the robust capability of ETP in detecting ethylene variations. As an innovative fluorescent probe, ETP provides a powerful tool for investigating ethylene signaling pathways and deepening our understanding of ethylene's role in plant growth, development, and stress responses.

The Mycobacterium tuberculosis cytochrome bcc:aa3 (cyt-bcc:aa3) oxidase is a validated drug target for tuberculosis treatment. In addition to telacebec (Q203), a clinical-stage drug candidate, several preclinical cyt-bcc:aa3 inhibitors have been reported. However, the bactericidal potency of cyt-bcc:aa3 inhibitors is limited by cytochrome bd oxidase (cyt-bd), an alternative terminal oxidase. We developed a high-throughput whole-mycobacteria assay to identify new cyt-bd inhibitors. Screening 115,398 small molecules identified several new chemical series, including a pyrazolo-quinazoline amine series. Chemical optimization yielded the potent derivative ETX1975-3, which, in combination with Q203, is bactericidal against M. tuberculosis, retains activity against a panel of M/XDR M. tuberculosis clinical isolates, and also shows efficacy against nontuberculous mycobacteria (NTM). Mode of action studies validated the cyt-bd target as the molecular target. While further chemical optimization is required, favorable microbiological, ADMET, and in vivo potency of ETX1975-3 makes it a promising preclinical candidate for tuberculosis and NTM infections.

The pathway involving the paralogous transcription factors Rtg1 and Rtg3 was first described in Saccharomyces cerevisiae as the retrograde regulation that adapts cellular metabolism in response to the state of mitochondrial respiration. We investigated the evolution of this pathway by studying its target genes in respiratory-deficient mutants of Candida albicans—a phylogenetically distant and metabolically distinct yeast species. We show that in C. albicans the Rtg pathway is also responsible for adaptation to cellular stresses related to respiratory dysfunction, but the repertoire of its target genes is different than in S. cerevisiae, and includes genes encoding proteins involved in alternative respiration, oxidative stress, mitophagy, and other aspects of metabolism. We also traced the evolution of the main components of the Rtg pathway and its target genes in the budding yeast (Saccharomycotina) subphylum. We show that the system originated within this clade following a single duplication of the gene encoding the ancestor of Rtg1 and Rtg3, but employs other factors, like the regulatory proteins Rtg2 and Mks1 that were likely present in the last common ancestor of budding yeasts. The regulation of the Rtg transcription factors in C. albicans is different than in S. cerevisiae, as both Rtg2 and Mks1 were lost in the majority of Serinales. Among the target genes, of particular interest is the evolution of the alternative oxidase (Aox), which was either lost or duplicated in multiple independent events. The presence of Aox strongly correlates with the mitochondrially encoded Complex I—a major source of oxidative stress.

Alternative oxidase and ethylene form a positive feed-forward loop in mitochondrial retrograde signaling.

Arachidin-2 suppresses Peronophythora litchii and postharvest decay of litchi fruit.

Itaconic acid (IA) is an important bio-based platform chemical produced via submerged fermentation by the filamentous Ascomycete Aspergillus terreus. In this study, we examined the impact of initial phosphate concentration on IA production from D-glucose and D-xylose in optimized, manganese-limited fermentations. Nine phosphate concentrations ranging from 0.04 to 4 g L−1 were tested, and representative low (0.04 g L−1), optimal (0.1 g L−1), and high (0.8 g L−1) conditions were analyzed in detail in controlled, 6 L scale bioreactors. Phosphate availability primarily influenced biomass formation and the biomass-to-product ratio rather than directly affecting IA accumulation. Both lower- and higher-than-optimal phosphate concentrations decreased the volumetric and specific IA yields, while the highest productivity was observed at 0.1 g L−1. Expression of the aoxA gene, encoding the cyanide-resistant alternative oxidase (AOX), and AOX enzymatic activity were inversely correlated with extracellular phosphate concentration, consistent with a role in redox homeostasis under phosphate-limited conditions. In contrast, total respiration rates and pellet-type morphology remained unaffected. These findings indicate that phosphate acts mainly as a secondary modulator of IA fermentation performance through its influence on biomass formation, whereas other metabolic constraints play a more dominant role in controlling IA overflow in A. terreus.