Coenzyme Q deficiency in endothelial mitochondria caused by hypoxia; remodeling of the respiratory chain and sensitivity to anoxia/reoxygenation.

This study examined the effects of hypoxia on coenzyme Q (Q) levels and mitochondrial function in EA. hy926 endothelial cells, shedding light on their responses to changes in oxygen levels. Chronic hypoxia during endothelial cell culture reduced Q synthesis by reducing hydroxy-methylglutaryl-CoA reductase (HMGCR) levels via hypoxia-inducible factor 1α (HIF1α), leading to severe Q deficiency. In endothelial mitochondria, hypoxia led to reorganization of the respiratory chain through upregulation of supercomplexes (I+III2+IV), forming a complete mitochondrial Q (mQ)-mediated electron transfer pathway. Mitochondria of endothelial cells cultured under hypoxic conditions showed reduced respiratory rates and membrane potential, as well as increased production of mitochondrial reactive oxygen species (mROS) as a result of increased mQ reduction levels (mQH2/mQtot). Anoxia/reoxygenation (A/R) in vitro caused impairment of endothelial mitochondria, manifested by reduced maximal respiration, complex III activity, membrane potential, coupling parameters, and increased mQ reduction and mROS production. Weaker A/R-induced changes compared to control mitochondria indicated better tolerance of A/R stress by the mitochondria of hypoxic cells. Moreover, in endothelial mitochondria, hypoxia-induced increases in uncoupling protein 3 (UCP3) and mitochondrial large-conductance Ca2+-activated potassium channel (mitoBKCa) levels and activities appear to have alleviated reoxygenation injury after A/R. These results not only highlight hypoxia-induced changes in mQ redox homeostasis and related mitochondrial function, but also indicate that chronic hypoxia during endothelial cell culture leads to mitochondrial adaptations that help mitochondria better withstand subsequent oxygen fluctuations.

Carbon dioxide and MAPK signalling: towards therapy for inflammation.

Inflammation, although necessary to fight infections, becomes a threat when it exceeds the capability of the immune system to control it. In addition, inflammation is a cause and/or symptom of many different disorders, including metabolic, neurodegenerative, autoimmune and cardiovascular diseases. Comorbidities and advanced age are typical predictors of more severe cases of seasonal viral infection, with COVID-19 a clear example. The primary importance of mitogen-activated protein kinases (MAPKs) in the course of COVID-19 is evident in the mechanisms by which cells are infected with SARS-CoV-2; the cytokine storm that profoundly worsens a patient's condition; the pathogenesis of diseases, such as diabetes, obesity, and hypertension, that contribute to a worsened prognosis; and post-COVID-19 complications, such as brain fog and thrombosis. An increasing number of reports have revealed that MAPKs are regulated by carbon dioxide (CO2); hence, we reviewed the literature to identify associations between CO2 and MAPKs and possible therapeutic benefits resulting from the elevation of CO2 levels. CO2 regulates key processes leading to and resulting from inflammation, and the therapeutic effects of CO2 (or bicarbonate, HCO3-) have been documented in all of the abovementioned comorbidities and complications of COVID-19 in which MAPKs play roles. The overlapping MAPK and CO2 signalling pathways in the contexts of allergy, apoptosis and cell survival, pulmonary oedema (alveolar fluid resorption), and mechanical ventilation-induced responses in lungs and related to mitochondria are also discussed. Video Abstract.

The bisphosphonates alendronate and zoledronate induce adaptations of aerobic metabolism in permanent human endothelial cells.

Nitrogen-containing bisphosphonates (NBPs), compounds that are widely used in the treatment of bone disorders, may cause side effects related to endothelial dysfunction. The aim of our study was to investigate the effects of chronic 6-day exposure to two common bone-preserving drugs, alendronate and zoledronate, on endothelial function and oxidative metabolism of cultured human endothelial cells (EA.hy926). NBPs reduced cell viability, induced oxidative stress and a pro-inflammatory state and downregulated the prenylation-dependent ERK1/2 signaling pathway in endothelial cells. In addition, NBPs induced increased anaerobic respiration and slightly increased oxidative mitochondrial capacity, affecting mitochondrial turnover through reduced mitochondrial fission. Moreover, by blocking the mevalonate pathway, NBPs caused a significant decrease in the level of coenzyme Q10, thereby depriving endothelial cells of an important antioxidant and mitochondrial electron carrier. This resulted in increased formation of reactive oxygen species (ROS), upregulation of antioxidant enzymes, and impairment of mitochondrial respiratory function. A general decrease in mitochondrial respiration occurred with stronger reducing fuels (pyruvate and glutamate) in NBP-treated intact endothelial cells, and significantly reduced phosphorylating respiration was observed during the oxidation of succinate and especially malate in NBP-treated permeabilized endothelial cells. The observed changes in oxidative metabolism caused a decrease in ATP levels and an increase in oxygen levels in NBP-treated cells. Thus, NBPs modulate the energy metabolism of endothelial cells, leading to alterations in the cellular energy state, coenzyme Q10 redox balance, mitochondrial respiratory function, and mitochondrial turnover.

Mitochondrial Coenzyme Q Redox Homeostasis and Reactive Oxygen Species Production.

Mitochondrial coenzyme Q (mtQ) of the inner mitochondrial membrane is a redox active mobile carrier in the respiratory chain that transfers electrons between reducing dehydrogenases and oxidizing pathway(s). mtQ is also involved in mitochondrial reactive oxygen species (mtROS) formation through the mitochondrial respiratory chain. Some mtQ-binding sites related to the respiratory chain can directly form the superoxide anion from semiubiquinone radicals. On the other hand, reduced mtQ (ubiquinol, mtQH2) recycles other antioxidants and directly acts on free radicals, preventing oxidative modifications. The redox state of the mtQ pool is a central bioenergetic patameter that alters in response to changes in mitochondrial function. It reflects mitochondrial bioenergetic activity and mtROS formation level, and thus the oxidative stress associated with the mitochondria. Surprisingly, there are few studies describing a direct relationship between the mtQ redox state and mtROS production under physiological and pathological conditions. Here, we provide a first overview of what is known about the factors affecting mtQ redox homeostasis and its relationship to mtROS production. We have proposed that the level of reduction (the endogenous redox state) of mtQ may be a useful indirect marker to assess total mtROS formation. A higher mtQ reduction level (mtQH2/mtQtotal) indicates greater mtROS formation. The mtQ reduction level, and thus the mtROS formation, depends on the size of the mtQ pool and the activity of the mtQ-reducing and mtQH2-oxidizing pathway(s) of respiratory chain. We focus on a number of physiological and pathophysiological factors affecting the amount of mtQ and thus its redox homeostasis and mtROS production level.

Endurance Training Increases the Running Performance of Untrained Men without Changing the Mitochondrial Volume Density in the Gastrocnemius Muscle.

The activity and quantity of mitochondrial proteins and the mitochondrial volume density (MitoVD) are higher in trained muscles; however, the underlying mechanisms remain unclear. Our goal was to determine if 20 weeks' endurance training simultaneously increases running performance, the amount and activity of mitochondrial proteins, and MitoVD in the gastrocnemius muscle in humans. Eight healthy, untrained young men completed a 20-week moderate-intensity running training program. The training increased the mean speed of a 1500 m run by 14.0% (p = 0.008) and the running speed at 85% of maximal heart rate by 9.6% (p = 0.008). In the gastrocnemius muscle, training significantly increased mitochondrial dynamics markers, i.e., peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α) by 23%, mitochondrial transcription factor A (TFAM) by 29%, optic artrophy-1 (OPA1) by 31% and mitochondrial fission factor (MFF) by 44%, and voltage-dependent anion channel 1 (VDAC1) by 30%. Furthermore, training increased the amount and maximal activity of citrate synthase (CS) by 10% and 65%, respectively, and the amount and maximal activity of cytochrome c oxidase (COX) by 57% and 42%, respectively, but had no effect on the total MitoVD in the gastrocnemius muscle. We concluded that not MitoVD per se, but mitochondrial COX activity (reflecting oxidative phosphorylation activity), should be regarded as a biomarker of muscle adaptation to endurance training in beginner runners.

Effects of Endurance Training on the Coenzyme Q Redox State in Rat Heart, Liver, and Brain at the Tissue and Mitochondrial Levels: Implications for Reactive Oxygen Species Formation and Respiratory Chain Remodeling.

Sixteen adult, 4-month-old male Wistar rats were randomly assigned to the training group (n = 8) or the control group (n = 8). We elucidated the effects of 8 weeks of endurance training on coenzyme Q (Q) content and the formation of reactive oxygen species (ROS) at the tissue level and in isolated mitochondria of the rat heart, liver and brain. We demonstrated that endurance training enhanced mitochondrial biogenesis in all tested organs, while a significant increase in the Q redox state was observed in the heart and brain, indicating an elevated level of QH2 as an antioxidant. Moreover, endurance training increased the mQH2 antioxidant pool in the mitochondria of the heart and liver, but not in the brain. At the tissue and isolated mitochondria level, an increase in ROS formation was only observed in the heart. ROS formation observed in the mitochondria of individual rat tissues after training may be associated with changes in the activity/amount of individual components of the oxidative phosphorylation system and its molecular organization, as well as with the size of the oxidized pool of mitochondrial Q acting as an electron carrier in the respiratory chain. Our results indicate that tissue-dependent changes induced by endurance training in the cellular and mitochondrial QH2 pool acting as an antioxidant and in the mitochondrial Q pool serving the respiratory chain may serve important roles in energy metabolism, redox homeostasis and the level of oxidative stress.

Carbon dioxide inhibits COVID-19-type proinflammatory responses through extracellular signal-regulated kinases 1 and 2, novel carbon dioxide sensors.

Mitogen-activated protein kinase (MAPK) signalling pathways are crucial for developmental processes, oncogenesis, and inflammation, including the production of proinflammatory cytokines caused by reactive oxygen species and upon severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. There are no drugs that can effectively prevent excessive inflammatory responses in endothelial cells in the lungs, heart, brain, and kidneys, which are considered the main causes of severe coronavirus disease 2019 (COVID-19). In this work, we demonstrate that human MAPKs, i.e. extracellular signal-regulated kinases 1 and 2 (ERK1/2), are CO2 sensors and CO2 is an efficient anti-inflammatory compound that exerts its effects through inactivating ERK1/2 in cultured endothelial cells when the CO2 concentration is elevated. CO2 is a potent inhibitor of cellular proinflammatory responses caused by H2O2 or the receptor-binding domain (RBD) of the spike protein of SARS-CoV-2. ERK1/2 activated by the combined action of RBD and cytokines crucial for the development of severe COVID-19, i.e. interferon-gamma (IFNγ) and tumour necrosis factor-α (TNFα), are more effectively inactivated by CO2 than by dexamethasone or acetylsalicylic acid in human bronchial epithelial cells. Previously, many preclinical and clinical studies showed that the transient application of 5-8% CO2 is safe and effective in the treatment of many diseases. Therefore, our research indicates that CO2 may be used for the treatment of COVID-19 as well as the modification of hundreds of cellular pathways.

Lung mitochondria adaptation to endurance training in rats.

We elucidated the impact of eight weeks of endurance training on the oxidative metabolism of rat lungs. Adult 3.5-month-old male rats were randomly allocated to a treadmill training group or a sedentary group as control. In the lungs, endurance training raised the expression level of the oxygen sensors hypoxia inducible factor 1α (HIF1α) and lysine-specific demethylase 6A (KDM6A) as well as stimulated mitochondrial oxidative capacity and mitochondrial biogenesis, while lactate dehydrogenase activity was reduced. Endurance training enhanced antioxidant systems (the coenzyme Q content and superoxide dismutase) in lung tissue but decreased them (and uncoupling protein 2) in lung mitochondria. In the lung mitochondria of trained rats, the decreased Q content and Complex I (CI) activity and the enhanced cytochrome pathway activity (CIII + CIV) may account for the diminished Q reduction level, resulting in a general decrease in H2O2 formation by mitochondria. Endurance training enhanced oxidation of glutamate and fatty acids and caused opposite effects in functional mitochondrial properties during malate and succinate oxidation, which were related to reduced activity of CI and increased activity of CII, respectively. In addition, endurance training downregulated CI in supercomplexes and upregulated CIII in the CIII2+CIV supercomplex in the oxidative phosphorylation system. We concluded that the adaptive lung responses observed could be due to hypoxia and oxidative stress induced by strenuous endurance training.

Expression profiling of the genes encoding ABA route components and the ACC oxidase isozymes in the senescing leaves of Populus tremula.

Abscisic acid (ABA) triggers and regulates, while ethylene modulates autumn leaf senescence. The expression profiles of genes encoding ABA route components and the ACC oxidase isozymes were investigated in Populus tremula during the early and moderate stages of autumn leaf senescence. The targets of interest were Ptre-HAB1-like genes (Ptre-HAB1, Ptre-HAB3a and Ptre-HAB3b), the subclass 3 of Ptre-SnRK2s genes (Ptre-SnRK2.6a, Ptre-SnRK2.6b and Ptre-SnRK2.6b) and Ptre-RbohD1, Ptre-RbohF1, and Ptre-RbohF2 genes encoding the poplar components, which are counterparts of the ABA route key regulators or the counterparts of its secondary messengers, such as Homology to ABA-insensitive 1 (HAB1), Sucrose non-fermenting 1-related protein kinases 2 (SnRK2s) or Respiratory burst oxidase D and Respiratory burst oxidase F (RbohD and RbohF, respectively) in Arabidopsis, and Ptre-ACO3, Ptre-ACO5, and Ptre-ACO6 genes encoding ACC oxidase isozymes involved in ethylene biosynthesis. The fold change in their expression levels enabled to distinguish the distinct expression patterns for the following pairs of genes: Ptre-HAB3a and Ptre-SnRK2.6a, Ptre-HAB3b and Ptre-SnRK2.2, and Ptre-HAB1 and Ptre-SnRK2.6b, where each pair involves the genes encoding the negative and positive regulators of ABA route, respectively. Among the investigated genes, the fold change of expression was the highest for Ptre-ACO3, Ptre-ACO6, and Ptre-SnRK2.6b genes during both the studied stages, and additionally for Ptre-HAB1 and Ptre-RbohD1 genes during the moderate stage. In contrast, the Ptre-RbohF1 and Ptre-RbohF2 genes exhibited only the transient upregulation at the early stage of senescence. In an in vitro study, the ability of protein kinases Ptre-SnRK2.6a and Ptre-SnRK2.6b to phosphorylate the N-terminal regions of Ptre-RbohD1 and Ptre-RbohF2 was studied; the activity of Ptre-SnRK2.6b against the studied Ptre-Rbohs was noticeably lower than that exhibited by Ptre-SnRK2.6a. It seems that despite the high similarity of their polypeptides, Ptre-SnRK2.6a and Ptre-SnRK2.6b may play different biological roles; nonetheless, it requires in vivo confirmation. Surprisingly, the highest protein kinase activity against the Ptre-Rbohs was detected in the heterologous reaction with AT-SnRK2.6/OST1 which suggests that the discussed interactions are evolutionary conserved.

The Influence of Statins on the Aerobic Metabolism of Endothelial Cells.

Endothelial mitochondrial dysfunction is considered to be the main cause of cardiovascular disease. The aim of this research was to elucidate the effects of cholesterol-lowering statins on the aerobic metabolism of endothelial cells at the cellular and mitochondrial levels. In human umbilical vein endothelial cells (EA.hy926), six days of exposure to 100 nM atorvastatin (ATOR) induced a general decrease in mitochondrial respiration. No changes in mitochondrial biogenesis, cell viability, or ATP levels were observed, whereas a decrease in Coenzyme Q10 (Q10) content was accompanied by an increase in intracellular reactive oxygen species (ROS) production, although mitochondrial ROS production remained unchanged. The changes caused by 100 nM pravastatin were smaller than those caused by ATOR. The ATOR-induced changes at the respiratory chain level promoted increased mitochondrial ROS production. In addition to the reduced level of mitochondrial Q10, the activity of Complex III was decreased, and the amount of Complex III in a supercomplex with Complex IV was diminished. These changes may cause the observed decrease in mitochondrial membrane potential and an increase in Q10 reduction level as a consequence, leading to elevated mitochondrial ROS formation. The above observations highlight the role of endothelial mitochondria in response to potential metabolic adaptations related to the chronic exposure of endothelial cells to statins.

Expression profiling of CTR1-like and EIN2-like genes in buds and leaves of Populus tremula, and in vitro study of the interaction between their polypeptides.

In Arabidopsis, the serine/threonine protein kinase Constitutive Triple Response 1 (CTR1) and Ethylene Insensitive 2 polypeptide (EIN2) functions are key negative and positive components, respectively, in the ethylene signalling route. Here, we report on an in silico study of members of the CTR1-like and EIN2-like polypeptide families from poplars. The expression of CTR1-like and EIN2-like genes such as Ptre-CTR1, Ptre-CTR3 and Ptre-EIN2a was studied in Populus tremula buds and leaves in response to dehydration, various light conditions and under senescence. In buds under dehydration, the maximal fold-change of the Ptre-CTR1, Ptre-CTR3 and Ptre-EIN2a expression level recorded almost identical values. This suggests that maintenance of a constant ratio between the transcript levels of genes encoding positive and negative ethylene signalling components is required under stress. The expression of the studied genes was 1.4-to 3-fold higher in response to darkness, but 4.5- to 51.2-fold and 21.6- to 51.2-fold higher under the early and moderate leaf senescence, respectively. It is worth noting that the senescence-related Ptre-EIN2a and Ptre-CTR3a expression profiles were very similar. Using in vitro assays, we demonstrated the ability of the catalytic domain of Ptre-CTR1 to phosphorylate the Ptre-EIN2a-like polypeptide, which is similar to that in Arabidopsis. The target substrate, the Ptre-CEND2a polypeptide (C-terminal part of Ptre-EIN2a), was only phosphorylated by the protein kinase Ptre-CTR1 and not by Ptre-CTR3. Moreover, the addition of Ptre-CTR3 polypeptides (-CTR3a or -CTR3b forms) to the reaction mixture had an inhibitory effect on Ptre-CTR1 auto- and trans-phosphorylation. In contrast to Ptre-CTR1, Ptre-CTR3 may act as a positive regulator in ethylene signalling in poplar; however, this hypothesis requires in vivo confirmation. Thus, the ethylene signalling route in poplar seems to be under the control of certain additional mechanisms which have not been reported in Arabidopsis.

Expression profiling of genes encoding ABA route components in response to dehydration or various light conditions in poplar buds and leaves.

In this report, the members of PP2C, SnRK2a and Rboh oxidase families from Arabidopsis and poplar were studied in silico, and the expression profiles of the some of them were specified in Populus tremula buds and adult leaves. In poplars, the counterparts of ABI1- and ABI2-like protein phosphatases are lacking, but poplar genomes encode three HAB-like proteins denoted in this work as HAB1, HAB3a and HAB3b, and the counterparts of the two latter ones are absent in Arabidopsis. Nonetheless, they may be present in other species. In poplars, SnRK2 subclass III includes two SnRK2.6-like protein kinases denoted by us as SnRK2.6a and SnRK2.6b, and only one SnRK2.2 corresponding to SnRK2.2 and SnRK2.3 ones from Arabidopsis. In contrast to Arabidopsis, the poplar Rboh family involves two RbohD- and RbohF-like proteins denoted here as RbohD1 and RbohD2, and RbohF1 and RbohF2, respectively. The expressions of genes encoding the above components of the ABA route were studied in Populus tremula dehydrated buds and adult leaves not subjected to stress but exposed to natural daylight or to darkness, and to inhibition of ethylene biosynthesis or signaling route by cobalt or silver ions, respectively. In leaves, the light conditions seemed to be the most pronounced factor, from among the studied stimuli, controlling the expression Ptre-HAB3a, Ptre-HAB1, Ptre-SnRK2.6a and Ptre-RbohF2 genes, their expression was upregulated in darkness. This observation implies that these genes may be important for dark-induced stomatal closure regulation. Ethylene negatively affected the expression of three studied Rboh genes and Ptre-HAB1one but only at daylight, whereas its positive effect on the of Ptre-HAB3a was shown in the dark exposed leaves. In buds, three studied Rboh genes took part in the early response to dehydration, however their participation involved the visibly highest level of the Ptre-RbohD1 transcripts, followed by Ptre-RbohF2 and the lowest one of Ptre-RbohF1. Nonetheless, the further stress-induced superoxide anion generation seemed to depend on the enhanced expression of the Ptre-RbohD1 and Ptre-RbohF2 genes only, still with a significantly higher level of the Ptre-RbohD1 one. Ptre-RbohD2 transcripts were found neither in leaves nor in buds. The expression of the other genes discussed in the present work was either slightly upregulated at moderate stress or did not significantly change in response to dehydration. The protein kinase activity of overexpressed Ptre-SnRK2.6a and Ptre-SnRK2.6b was confirmed in in vitro protein kinase assay and compared to that of SnRK2.6/OST1 one from Arabidopsis.

Nuclear speckles: molecular organization, biological function and role in disease.

The nucleoplasm is not homogenous; it consists of many types of nuclear bodies, also known as nuclear domains or nuclear subcompartments. These self-organizing structures gather machinery involved in various nuclear activities. Nuclear speckles (NSs) or splicing speckles, also called interchromatin granule clusters, were discovered as sites for splicing factor storage and modification. Further studies on transcription and mRNA maturation and export revealed a more general role for splicing speckles in RNA metabolism. Here, we discuss the functional implications of the localization of numerous proteins crucial for epigenetic regulation, chromatin organization, DNA repair and RNA modification to nuclear speckles. We highlight recent advances suggesting that NSs facilitate integrated regulation of gene expression. In addition, we consider the influence of abundant regulatory and signaling proteins, i.e. protein kinases and proteins involved in protein ubiquitination, phosphoinositide signaling and nucleoskeletal organization, on pre-mRNA synthesis and maturation. While many of these regulatory proteins act within NSs, direct evidence for mRNA metabolism events occurring in NSs is still lacking. NSs contribute to numerous human diseases, including cancers and viral infections. In addition, recent data have demonstrated close relationships between these structures and the development of neurological disorders.

AtEAF1 is a potential platform protein for Arabidopsis NuA4 acetyltransferase complex.

BACKGROUND: Histone acetyltransferase complex NuA4 and histone variant exchanging complex SWR1 are two chromatin modifying complexes which act cooperatively in yeast and share some intriguing structural similarities. Protein subunits of NuA4 and SWR1-C are highly conserved across eukaryotes, but form different multiprotein arrangements. For example, the human TIP60-p400 complex consists of homologues of both yeast NuA4 and SWR1-C subunits, combining subunits necessary for histone acetylation and histone variant exchange. It is currently not known what protein complexes are formed by the plant homologues of NuA4 and SWR1-C subunits. RESULTS: We report on the identification and molecular characterization of AtEAF1, a new subunit of Arabidopsis NuA4 complex which shows many similarities to the platform protein of the yeast NuA4 complex. AtEAF1 copurifies with Arabidopsis homologues of NuA4 and SWR1-C subunits ARP4 and SWC4 and interacts physically with AtYAF9A and AtYAF9B, homologues of the YAF9 subunit. Plants carrying a T-DNA insertion in one of the genes encoding AtEAF1 showed decreased FLC expression and early flowering, similarly to Atyaf9 mutants. Chromatin immunoprecipitation analyses of the single mutant Ateaf1b-2 and artificial miRNA knock-down Ateaf1 lines showed decreased levels of H4K5 acetylation in the promoter regions of major flowering regulator genes, further supporting the role of AtEAF1 as a subunit of the plant NuA4 complex. CONCLUSIONS: Growing evidence suggests that the molecular functions of the NuA4 and SWR1 complexes are conserved in plants and contribute significantly to plant development and physiology. Our work provides evidence for the existence of a yeast-like EAF1 platform protein in A. thaliana, filling an important gap in the knowledge about the subunit organization of the plant NuA4 complex.

Arabidopsis protein phosphatase 2C ABI1 interacts with type I ACC synthases and is involved in the regulation of ozone-induced ethylene biosynthesis.

Ethylene plays a crucial role in various biological processes and therefore its biosynthesis is strictly regulated by multiple mechanisms. Posttranslational regulation, which is pivotal in controlling ethylene biosynthesis, impacts 1-aminocyclopropane 1-carboxylate synthase (ACS) protein stability via the complex interplay of specific factors. Here, we show that the Arabidopsis thaliana protein phosphatase type 2C, ABI1, a negative regulator of abscisic acid signaling, is involved in the regulation of ethylene biosynthesis under oxidative stress conditions. We found that ABI1 interacts with ACS6 and dephosphorylates its C-terminal fragment, a target of the stress-responsive mitogen-activated protein kinase, MPK6. In addition, ABI1 controls MPK6 activity directly and by this means also affects the ACS6 phosphorylation level. Consistently with this, ozone-induced ethylene production was significantly higher in an ABI1 knockout strain (abi1td) than in wild-type plants. Importantly, an increase in stress-induced ethylene production in the abi1td mutant was compensated by a higher ascorbate redox state and elevated antioxidant activities. Overall, the results of this study provide evidence that ABI1 restricts ethylene synthesis by affecting the activity of ACS6. The ABI1 contribution to stress phenotype underpins its role in the interplay between the abscisic acid (ABA) and ethylene signaling pathways.

VDAC contributes to mRNA levels in Saccharomyces cerevisiae cells by the intracellular reduction/oxidation state dependent and independent mechanisms.

Available data suggest that voltage-dependent anion selective channel (VDAC) constitutes an important component of a cellular regulatory mechanism based on the intracellular reduction/oxidation (redox) state. Here, using quantitative RT-PCR, we demonstrated that depletion of VDAC1 (termed here VDAC) in Saccharomyces cerevisiae cells distinctly affected levels of mRNAs encoding nuclear proteins sensitive to changes of the intracellular redox state including the nuclear transcription factors important for adaptation to the redox state and proteins involved in communication between mitochondria and the nucleus. We also revealed that the changes of the studied protein transcript levels generally correlated with changes of the intracellular redox state although VDAC appears also to affect mRNA levels by a mechanism not based on changes of the intracellular redox states. Thus, VDAC seems to be an important element of the intracellular signaling network.

Genome sequence comparison of Col and Ler lines reveals the dynamic nature of Arabidopsis chromosomes.

Large differences in plant genome sizes are mainly due to numerous events of insertions or deletions (indels). The balance between these events determines the evolutionary direction of genome changes. To address the question of what phenomena trigger these alterations, we compared the genomic sequences of two Arabidopsis thaliana lines, Columbia (Col) and Landsberg erecta (Ler). Based on the resulting alignments large indels (>100 bp) within these two genomes were analysed. There are approximately 8500 large indels accounting for the differences between the two genomes. The genetic basis of their origin was distinguished as three main categories: unequal recombination (Urec)-derived, illegitimate recombination (Illrec)-derived and transposable elements (TE)-derived. A detailed study of their distribution and size variation along chromosomes, together with a correlation analyses, allowed us to demonstrate the impact of particular recombination-based mechanisms on the plant genome evolution. The results show that unequal recombination is not efficient in the removal of TEs within the pericentromeric regions. Moreover, we discovered an unexpectedly high influence of large indels on gene evolution pointing out significant differences between the various gene families. For the first time, we present convincing evidence that somatic events do play an important role in plant genome evolution.