Deficiency Of Cytochrome Research Articles

Human induced pluripotent stem cells (hiPSCs) derived cells reflect tissue specificity found in patients with Leigh syndrome French Canadian variant (LSFC).

Leigh syndrome French Canadian type (LSFC) is a recessive neurodegenerative disease characterized by tissue-specific deficiency in cytochrome c oxidase (COX), the fourth complex in the oxidative phosphorylation system. LSFC is caused by mutations in the leucine rich pentatricopeptide repeat containing gene (LRPPRC). Most LSFC patients in Quebec are homozygous for an A354V substitution that causes a decrease in the expression of the LRPPRC protein. While LRPPRC is ubiquitously expressed and is involved in multiple cellular functions, tissue-specific expression of LRPPRC and COX activity is correlated with clinical features. In this proof-of-principle study, we developed human induced pluripotent stem cell (hiPSC)-based models from fibroblasts taken from a patient with LSFC, homozygous for the LRPPRC*354V allele, and from a control, homozygous for the LRPPRC*A354 allele. Specifically, for both of these fibroblast lines we generated hiPSC, hiPSC-derived cardiomyocytes (hiPSC-CMs) and hepatocyte-like cell (hiPSC-HLCs) lines, as well as the three germ layers. We observed that LRPPRC protein expression is reduced in all cell lines/layers derived from LSFC patient compared to control cells, with a reduction ranging from ∼70% in hiPSC-CMs to undetectable levels in hiPSC-HLC, reflecting tissue heterogeneity observed in patient tissues. We next performed exploratory analyses of these cell lines and observed that COX protein expression was reduced in all cell lines derived from LSFC patient compared to control cells. We also observed that mutant LRPPRC was associated with altered expression of key markers of endoplasmic reticulum stress response in hiPSC-HLCs but not in other cell types that were tested. While this demonstrates feasibility of the approach to experimentally study genotype-based differences that have tissue-specific impacts, this study will need to be extended to a larger number of patients and controls to not only validate the current observations but also to delve more deeply in the pathogenic mechanisms of LSFC.

Clinical and genetic characteristics of children with COX20-associated mitochondrial disorder: case report and literature review

BackgroundThe deficiency of cytochrome c oxidase 20 is a rare autosomal recessive mitochondrial disorder characterized by ataxia, dysarthria, dystonia and sensory neuropathy.Case presentationIn this study, we describe a patient from a non-consanguineous family exhibiting developmental delay, ataxia, hypotonia, dysarthria, strabismus, visual impairment and areflexia. An examination of nerve conduction showed a normal result at first but revealed axonal sensory neuropathy later. This situation has not been reported in any literatures. The whole-exome sequencing analysis revealed that the patient harbored compound heterozygous mutations (c.41 A > G and c.259G > T) of the COX20 gene. By literature review, 5 patients carried the same compound heterozygous mutations.ConclusionCOX20 might be considered as a potential gene for the early-onset ataxia and the axonal sensory neuropathy. Our patient exhibited strabismus and visual impairment, which expands the clinical presentation of COX20 related mitochondrial disorders caused by the compound heterozygous variants (c.41 A > G and c.259G > T). However, a clear genotype/phenotype correlation has not yet been established. Additional researches and cases are needed to further confirm the correlation.

Severe multisystem pathology, metabolic acidosis, mitochondrial dysfunction, and early death associated with an X-linked AIFM1 variant.

Variants in the X-linked gene AIFM1 (apoptosis-inducing factor mitochondria-associated 1) are associated with a highly variable clinical presentation that encompasses motor neuropathy, ataxia, encephalopathies, deafness, and cognitive impairment. AIFM1 encodes a mitochondrial flavin adenine dinucleotide (FAD)-dependent nicotinamide adenine dinucleotide (NADH) oxidoreductase, with roles in the regulation of respiratory complex assembly and function, production of reactive oxygen species, and the coordination of a caspase-independent type of apoptosis known as parthanatos. In this report, we describe a missense AIFM1 variant (absent in reference population databases; c.506C > T, p.Pro169Leu) identified in the proband and sibling of a family with three affected males. The proband, his brother, and their maternal uncle all exhibited severe multisystem pathology, metabolic acidosis, and early demise. Metabolic testing on the proband revealed normal activity of the pyruvate dehydrogenase complex in skin fibroblasts. Absent or partial deficiency of cytochrome c oxidase was found in muscle fibers, however, supporting a Complex IV mitochondrial deficiency. Functional studies carried out on fibroblasts from the proband demonstrated reduced steady state levels of the AIFM1 protein, decreased Complex I subunit abundance, elevated sensitivity to the apoptosis inducer staurosporine, and increased nuclear condensation when grown in galactose-containing media. The reduced abundance of AIFM1 in the patient cells could not be stabilized with riboflavin or protease inhibitor treatment. Together, these findings suggest that the normal function of the AIFM1 gene product within mitochondria, and its response to apoptotic stimuli, are impaired by this variant, likely accounting for the severity of the phenotype seen in these patients. These findings also imply tissue-specific effects of this variant on different mitochondrial complexes. This study expands the genetic and phenotypic spectrum associated with AIFM1 variants, with the combination of exome sequencing and functional studies allowing a diagnosis to finally be confirmed for this family.

A deletion variant partially complements a porin-less strain of Neurospora crassa.

Mitochondrial porin, the voltage-dependent anion channel, plays an important role in metabolism and other cellular functions within eukaryotic cells. To further the understanding of porin structure and function, Neurospora crassa wild-type porin was replaced with a deletion variant lacking residues 238-242 (238porin). 238porin was assembled in the mitochondrial outer membrane, but the steady state levels were only about 3% of those of the wild-type protein. The strain harbouring 238porin displayed cytochrome deficiencies and expressed alternative oxidase. Nonetheless, it exhibited an almost normal linear growth rate. Analysis of mitochondrial proteomes from a wild-type strain FGSC9718, a strain lacking porin (ΔPor-1), and one expressing only 238porin, revealed that the major differences between the variant strains were in the levels of subunits of the NADH:ubiquinone oxidoreductase (complex I) of the electron transport chain, which were reduced only in the ΔPor-1 strain. These, and other proteins related to electron flow and mitochondrial biogenesis, are differentially affected by relative porin levels.

Biotin deprivation impairs mitochondrial structure and function and has implications for inherited metabolic disorders.

Certain inborn errors of metabolism result from deficiencies in biotin containing enzymes. These disorders are mimicked by dietary absence or insufficiency of biotin, ATP deficit being a major effect,whose responsible mechanisms have not been thoroughly studied. Here we show that in rats and cultured cells it is the result of reduced TCA cycle flow, partly due to deficient anaplerotic biotin-dependent pyruvate carboxylase. This is accompanied by diminished flow through the electron transport chain, augmented by deficient cytochrome c oxidase (complex IV) activity with decreased cytochromes and reduced oxidative phosphorylation. There was also severe mitochondrial damage accompanied by decrease of mitochondria, associated with toxic levels of propionyl CoA as shown by carnitine supplementation studies, which explains the apparently paradoxical mitochondrial diminution in the face of the energy sensor AMPK activation, known to induce mitochondria biogenesis. This idea was supported by experiments on AMPK knockout mouse embryonic fibroblasts (MEFs). The multifactorial ATP deficit also provides a plausible basis for the cardiomyopathy in patients with propionic acidemia, and other diseases.Additionally, systemic inflammation concomitant to the toxic state might explain our findings of enhanced IL-6, STAT3 and HIF-1α, associated with an increase of mitophagic BNIP3 and PINK proteins, which may further increase mitophagy. Together our results imply core mechanisms of energy deficit in several inherited metabolic disorders.

Cell lineage tracing in human epithelial tissues using mitochondrial DNA mutations as clonal markers.

The study of cell lineages through heritable genetic lineage tracing is well established in experimental animals, particularly mice. While such techniques are not feasible in humans, we have taken advantage of the fact that the mitochondrial genome is highly prone to nonpathogenic mutations and such mutations can be used as clonal markers to identify stem cell derived clonal populations in human tissue sections. A mitochondrial DNA (mtDNA) mutation can spread by a stochastic process through the several copies of the circular genome in a single mitochondrion, and then through the many mitochondria in a single cell, a process called 'genetic drift.' This process takes many years and so is likely to occur only in stem cells, but once established, the fate of stem cell progeny can be followed. A cell having at least 80% of its mtDNA genomes bearing the mutation results in a demonstrable deficiency in mtDNA-encoded cytochrome c oxidase (CCO), optimally detected in frozen tissue sections by dual-color histochemistry, whereby CCO activity stains brown and CCO deficiency is highlighted by subsequent succinate dehydrogenase activity, staining the CCO-deficient areas blue. Cells with CCO deficiency can be laser captured and subsequent mtDNA sequencing can ascertain the nature of the mutation. If all cells in a CCO-deficient area have an identical mutation, then a clonal population has been identified; the chances of the same mutation initially arising in separate cells are highly improbable. The technique lends itself to the study of both normal epithelia and can answer several questions in tumor biology. WIREs Dev Biol 2016, 5:103-117. doi: 10.1002/wdev.203 For further resources related to this article, please visit the WIREs website.

Mitochondrial vulnerability and increased susceptibility to nutrient-induced cytotoxicity in fibroblasts from leigh syndrome French canadian patients.

Mutations in LRPPRC are responsible for the French Canadian variant of Leigh Syndrome (LSFC), a severe disorder characterized biochemically by a tissue-specific deficiency of cytochrome c oxidase (COX) and clinically by the occurrence of severe and deadly acidotic crises. Factors that precipitate these crises remain unclear. To better understand the physiopathology and identify potential treatments, we performed a comprehensive analysis of mitochondrial function in LSFC and control fibroblasts. Furthermore, we have used this cell-based model to screen for conditions that promote premature cell death in LSFC cells and test the protective effect of ten interventions targeting well-defined aspects of mitochondrial function. We show that, despite maintaining normal ATP levels, LSFC fibroblasts present several mitochondrial functional abnormalities under normal baseline conditions, which likely impair their capacity to respond to stress. This includes mitochondrial network fragmentation, impaired oxidative phosphorylation capacity, lower membrane potential, increased sensitivity to Ca2+-induced permeability transition, but no changes in reactive oxygen species production. We also show that LSFC fibroblasts display enhanced susceptibility to cell death when exposed to palmitate, an effect that is potentiated by high lactate, while high glucose or acidosis alone or in combination were neutral. Furthermore, we demonstrate that compounds that are known to promote flux through the electron transport chain independent of phosphorylation (methylene blue, dinitrophenol), or modulate fatty acid (L-carnitine) or Krebs cycle metabolism (propionate) are protective, while antioxidants (idebenone, N-acetyl cysteine, resveratrol) exacerbate palmitate plus lactate-induced cell death. Collectively, beyond highlighting multiple alterations in mitochondrial function and increased susceptibility to nutrient-induced cytotoxicity in LSFC fibroblasts, these results raise questions about the nature of the diets, particularly excess fat intake, as well as on the use of antioxidants in patients with LSFC and, possibly, other COX defects.

Identification of Oma1p Protease Sensitive Sites in Subunit 1 of Yeast Cytochrome Oxidase

Cytochrome c oxidase is the terminal electron acceptor in the electron transport chain in many aerobic organisms. This multi‐protein complex can be composed of a varying number of subunits depending on species. In the budding yeast, Saccharomyces cerevisiae, cytochrome c oxidase is made up of 11 subunits, 8 are derived from the nuclear genome and 3 are derived from the mitochondrial genome. To ensure these subunits come together at the correct time and place a family of assembly factors is required. In the case of the mitochondrial DNA encoded subunit 1 there is a linear pathway of biosynthesis where these assembly factors and other structural subunits associate at specific times to regulate specific maturation events. In the absence of some assembly factors subunit 1 is subject to degradation by the protease Oma1p. In yeast, this results in a deficiency in cytochrome c oxidase activity and the inability to grow using substrates requiring intact oxidative phosphorylation. We have performed a mutagenic screen of mitochondrial DNA to identify mutations in the subunit 1 gene that can suppress the oxidative phosphorylation deficient phenotype caused by the absence of the assembly factors, COA2 and SHY1. Through analysis of the COX1 gene we will identify putative regions required for the proteolytic processing of subunit 1 by the Oma1p protease. The information gathered from this research will guide us in identifying putative regions required for cytochrome c oxidase subunit 1 degradation and also provide more information regarding the proteolytic requirements of the Oma1p protease.

Clinical, Pathological, and Neuroimaging Analyses of Two Cases of Leigh Syndrome in a Chinese Family

In this study, the authors examined the clinical manifestations, skeletal muscle pathological characteristics, and neuroimaging results of 2 cases of Leigh syndrome in a Chinese family. The 2 patients presented with general weakness, and 1 of them presented with an impairment of vision. Skeletal muscle biopsies showed a deficiency in cytochrome c oxidase levels. Brain magnetic resonance imaging showed increased T1 and T2 signal intensities in the centrum ovale and dentate nucleus. Diffusion-weighted imaging showed a high-intensity signal. Magnetic resonance spectroscopy showed elevated levels of lactic acid in lesions. The examination of 1 patient at disease onset and during disease remission showed that the lesions detected by magnetic resonance imaging and diffusion-weighted imaging, and the peak for lactic acid detected by magnetic resonance spectroscopy, decreased during remission. These data suggest that changes in the imaging results of patients with Leigh syndrome correlate with disease course and pathogenetic condition.

Partial tandem duplication of mtDNA–tRNA Phe impairs mtDNA translation in late-onset mitochondrial myopathy

An 80-year-old woman (PI) has been suffering of late onset progressive weakness and wasting of lower-limb muscles, accompanied by high creatine kinase levels in blood. A muscle biopsy, performed at 63 years, showed myopathic features with partial deficiency of cytochrome c oxidase. A second biopsy taken 7 years later confirmed the presence of a mitochondrial myopathy but also of vacuolar degeneration and other morphological features resembling inclusion body myopathy. Her 46-year-old daughter (PII) and 50-year-old son (PIII) are clinically normal, but the creatine kinase levels were moderately elevated and the EMG was consistently myopathic in both. Analysis of mitochondrial DNA sequence revealed in all three patients a novel, homoplasmic 15 bp tandem duplication adjacent to the 5′ end of mitochondrial tRNA Phe gene, encompassing the first 11 nucleotides of this gene and the four terminal nucleotides of the adjacent D-loop region. Both mutant fibroblasts and cybrids showed low oxygen consumption rate, reduced mitochondrial protein synthesis, and decreased mitochondrial tRNA Phe amount. These findings are consistent with an unconventional pathogenic mechanism causing the tandem duplication to interfere with the maturation of the mitochondrial tRNA Phe transcript.

Mitochondrial dysfunction resulting from the absence of mitochondrial porin in Neurospora crassa

Porin, the voltage-dependent anion-selective channel (VDAC) in the mitochondrial outer membrane, contributes to metabolism and apoptosis. VDAC function was investigated in Neurospora, an obligate aerobe with a single porin. Porinless strains are viable, with cold-sensitive growth, cytochrome deficiencies and overexpression of alternative oxidase. iTRAQ labeling of mitochondria from a porinless strain and its progenitor revealed a small group of proteins with altered expression levels in the mutant organelles. Porinless Neurospora appears to compensate not by inducing alternative pores, but by altering electron flow and nucleotide metabolism. Transcriptional and post-transcriptional mechanisms contribute to the response, reflecting the extent of porin influence.

LRPPRC and SLIRP interact in a ribonucleoprotein complex that regulates posttranscriptional gene expression in mitochondria.

Mutations in LRPPRC are responsible for the French Canadian variant of Leigh syndrome (LSFC), a neurodegenerative disorder caused by a tissue-specific deficiency in cytochrome c oxidase (COX). To investigate the pathogenic mechanism of disease, we studied LRPPRC function in LSFC and control fibroblasts. The level of mutated LRPPRC is reduced in LSFC cells, and this results in decreased steady-state levels of most mitochondrial mRNAs, but not rRNAs or tRNAs, a phenotype that can be reproduced by siRNA-mediated knockdown of LRPPRC in control cells. Processing of the primary transcripts appears normal. The resultant defect in mitochondrial protein synthesis in LSFC cells disproportionately affects the COX subunits, leading to an isolated COX assembly defect. Further knockdown of LRPPRC produces a generalized assembly defect in all oxidative phosphorylation complexes containing mtDNA-encoded subunits, due to a severe decrease in all mitochondrial mRNAs. LRPPRC exists in a high-molecular-weight complex, and it coimmunoprecipitates with SLIRP, a stem-loop RNA-binding protein. Although this interaction does not depend on mitochondrial mRNA, both proteins show reduced stability in its absence. These results implicate LRPPRC in posttranscriptional mitochondrial gene expression as part of a ribonucleoprotein complex that regulates the stability and handling of mature mRNAs.

A homozygous mutation in the SCO2 gene causes a spinal muscular atrophy like presentation with stridor and respiratory insufficiency

Infants with deficiency of cytochrome c oxidase (COX) due to SCO2 mutations observed so far usually demonstrated early cardiomyopathy, encephalopathy and lactic acidosis. Milder spinal muscular atrophy-like (SMA-like) phenotype was also rarely reported. The aim is to present 18 Polish patients with SCO2 mutations. Molecular study revealed p.E140K mutation in all cases (on 32 alleles); p.Q53X mutation and novel p.M177T change were identified in single patients. In three families no second mutation was found. Thirteen p.E140K homozygotes presented in infancy with floppiness and remarkable stridor. Survival motor neuron ( SMN) gene deletion was excluded. Mild to moderate lactic academia was found. Neurological involvement manifested as spasticity and psychomotor retardation. In some patients strabismus, ptosis and episodes of seizures were seen. During second half of the year chronic respiratory failure with artificial respiration dependency appeared in all homozygotes. Heart involvement was never present at the beginning. Rapidly progressive hypertrophic cardiomyopathy developed in several patients at the terminal stage. The stridor was constant and striking feature. Skeletal muscle biopsy was performed in 16 patients including 11 homozygotes. Four pathological patterns were discerned – from neurogenic muscle changes, including spinal muscular atrophy (SMA) to unspecific findings. Histochemical cytochrome c oxidase (COX) deficit was not a constant feature. Significant decrease in respiratory chain complex IV activity was detected in muscle homogenate by spectrophotometric method only in 7 out of 12 examined cases. Conclusions 1/Mutations of SCO2 gene should be considered as a possible cause of neurogenic skeletal muscle features (including SMA-like) in infants with encephalomyopathy even in the absence of heart involvement and COX deficit; 2/Inspiratory stridor may be symptomatic of SCO2 gene mutation(s).

Cardiac Cytochrome c Oxidase Activity and Contents of Subunits 1 and 4 Are Altered in Offspring by Low Prenatal Copper Intake by Rat Dams

It has been reported previously that the offspring of rat dams consuming low dietary copper (Cu) during pregnancy and lactation experience a deficiency in cardiac cytochrome c oxidase (CCO) characterized by reduced catalytic activity and mitochondrial and nuclear subunit content after postnatal d 10. The present study was undertaken to determine whether the cardiac CCO deficiency was caused directly by low postnatal Cu intake or whether it was a prenatal effect of low Cu intake by the dams that became manifest postnatally. Dams were fed either a Cu-adequate diet (6 mg Cu/kg) or Cu-deficient diet (1 mg Cu/kg) beginning 3 wk before conception and throughout gestation and lactation. One day following parturition, several litters from Cu-adequate dams were cross fostered to Cu-deficient dams and several litters from Cu-deficient dams were cross fostered to Cu-adequate dams. Litters that remained with their birth dams served as controls. CCO activity, the content of the mitochondrial-encoded CCO subunit 1 (COX1), and the content of the nuclear-encoded subunit COX4 in cardiac mitochondria were reduced in the 21-d-old offspring of Cu-deficient dams. COX1 content was normal in the 21-d-old cross-fostered offspring of Cu-deficient dams, but CCO activity and COX4 were reduced. Cross fostering the offspring of Cu-adequate dams to Cu-deficient dams did not significantly affect CCO activity, COX1 content, or COX4 content in cardiac mitochondria of 21-d-old offspring. These data indicate that low prenatal Cu intake by dams was the determinant of CCO activity in cardiac mitochondria of the 21-d-old offspring and may have led to the assembly of a less-than-fully active holoenzyme.

A mitochondrial myopathy characterised by a deficiency in reducible cytochrome b. By JA Morgan-Hughes, P Darveniza, SN Kahn, DN Langdon, RM Sherratt, JM Land and JB Clark (From the Institute of Neurology, Queen Square, London WC1 and the Biochemistry Department, St Bartholomew's Hospital Medical College, London EC1) Brain 1977; 100: 617-640.

Hitherto, morphological changes seen in mitochondria obtained from samples of skeletal muscle in a variety of neuromuscular disorders have not been correlated with functional abnormalities and so have not been considered significant for the pathogenesis of these conditions. But more recently, investigators from Cornell University have linked these same ultrastructural features to a primary biochemical abnormality of mitochondrial function. The evidence hints at a disturbance of cellular respiration in the presence of various substrates. In Luft's disease, hyper-metabolism (not of thyroid origin) is observed but, for the rest, insights into the disease mechanisms are lacking. Now that situation changes. ‘The present paper reports the findings in a man whose weakness and striking muscular fatigability appeared to be due to a primary disturbance of mitochondrial function. Biochemical studies of isolated mitochondrial fractions have shown a specific deficiency of reducible cytochrome b’. N.T., now aged 38 years, has had weakness and muscle fatigue since early childhood and has not been able to run or play games from his mid-teens. Nor was he able to continue his apprenticeship as a tailor through inability to work the foot-operated treadle of a sewing machine. Later, some bulbar symptoms emerged. Cold and alcohol seem to make him worse. On examination, he is short in stature with normal appearing if somewhat wasted muscles but showing weakness of the face (sparing the eyelids and eye movements), neck, and shoulder and pelvic girdles. The tendon reflexes are absent in the legs. ‘The most striking abnormality was a marked and progressive increase in muscle weakness during sustained activity … or repetitive manoeuvres … after a few minutes of complete rest, muscle strength returned to its pre-exercise level’. Screening investigations show only an excess of urinary lactate and pyruvate. Routine electromyography is equally unremarkable although his ability to exert maximal voluntary …

Prenatal copper deficiency in rat dams causes persistent reduction in nuclear‐encoded cytochrome c oxidase subunits in cardiac mitochondria of the first generation

Previous studies have shown that the offspring of rat dams having low copper (Cu) intake during pregnancy and lactation experience a deficiency in cardiac cytochrome c oxidase (CCO) after postnatal day 10. The present study was undertaken to determine the relative influences of pre‐and postnatal Cu intake on CCO subunit content in cardiac mitochondria by cross fostering pups from dams fed AIN93G diet containing 1 mg Cu/kg (CuD dams) to dams fed diet containing 6 mg Cu/kg (CuA dams) and vice versa on postnatal day (PND) 1. Pups that remained with their birth dams served as controls. All dams began dietary treatment with either CuD or CuA diets 3 weeks before conception and remained on their respective diets until PND 21. On PND 21, no differences in the content of the mitochondrial‐encoded COX1 subunit occurred between the offspring of CuA dams, offspring of CuA dams cross fostered to CuD dams and offspring of CuD dams cross fostered to CuA dams. However, COX1 content was reduced 42% in the non‐cross fostered offspring of CuD dams. The content of the nuclear‐encoded COX4 subunit was reduced 28% in the offspring of CuD dams and the offspring of CuD dams cross fostered to CuA dams. These findings indicate that low prenatal Cu intake causes a persistent reduction in nuclear‐, but not mitochondrial‐encoded, CCO subunits in cardiac mitochondria in the F1 generation.

Early Developmental Pathology Due to Cytochrome c Oxidase Deficiency Is Revealed by a New Zebrafish Model

Deficiency of cytochrome c oxidase (COX) is associated with significant pathology in humans. However, the consequences for organogenesis and early development are not well understood. We have investigated these issues using a zebrafish model. COX deficiency was induced using morpholinos to reduce expression of CoxVa, a structural subunit, and Surf1, an assembly factor, both of which impaired COX assembly. Reduction of COX activity to 50% resulted in developmental defects in endodermal tissue, cardiac function, and swimming behavior. Cellular investigations revealed different underlying mechanisms. Apoptosis was dramatically increased in the hindbrain and neural tube, and secondary motor neurons were absent or abnormal, explaining the motility defect. In contrast, the heart lacked apoptotic cells but showed increasingly poor performance over time, consistent with energy deficiency. The zebrafish model has revealed tissue-specific responses to COX deficiency and holds promise for discovery of new therapies to treat mitochondrial diseases in humans.

Light and electron microscopy characteristics of the muscle of patients with SURF1 gene mutations associated with Leigh disease

Aims:Leigh syndrome (LS) is characterised by almost identical brain changes despite considerable causal heterogeneity. SURF1 gene mutations are among the most frequent causes of LS. Although deficiency of cytochrome c...

Deficiency of cytochrome c oxidase has severe consequences for development in zebrafish

Deficiency of cytochrome c oxidase has severe consequences for development in zebrafish

Cytochrome b gene structure and consequences for resistance to Qo inhibitor fungicides in plant pathogens

The cytochrome b (cyt b) gene structure was characterized for different agronomically important plant pathogens, such as Puccinia recondita f sp tritici (Erikss) CO Johnston, P graminis f sp tritici Erikss and Hennings, P striiformis f sp tritici Erikss, P coronata f sp avenae P Syd & Syd, P hordei GH Otth, P recondita f sp secalis Roberge, P sorghi Schwein, P horiana Henn, Uromyces appendiculatus (Pers) Unger, Phakopsora pachyrhizi Syd & P Syd, Hemileia vastatrix Berk & Broome, Alternaria solani Sorauer, A alternata (Fr) Keissl and Plasmopara viticola (Berk & Curt) Berlese & de Toni. The sequenced fragment included the two hot spot regions in which mutations conferring resistance to QoI fungicides may occur. The cyt b gene structure of these pathogens was compared with that of other species from public databases, including the strobilurin-producing fungus Mycena galopoda (Pers) P Kumm, Saccharomyces cerevisiae Meyer ex Hansen, Venturia inaequalis (Cooke) Winter and Mycosphaerella fijiensis Morelet. In all rust species, as well as in A solani, resistance to QoI fungicides caused by the mutation G143A has never been reported. A type I intron was observed directly after the codon for glycine at position 143 in these species. This intron was absent in pathogens such as A alternata, Blumeria graminis (DC) Speer, Pyricularia grisea Sacc, Mycosphaerella graminicola (Fuckel) J Schröt, M fijiensis, V inaequalis and P viticola, in which resistance to QoI fungicides has occurred and the glycine is replaced by alanine at position 143 in the resistant genotype. The present authors predict that a nucleotide substitution in codon 143 would prevent splicing of the intron, leading to a deficient cytochrome b, which is lethal. As a consequence, the evolution of resistance to QoI fungicides based on G143A is not likely to evolve in pathogens carrying an intron directly after this codon.