Two Related RNA-editing Proteins Target the Same Sites in Mitochondria of Arabidopsis thaliana

The facilitators for specific cytosine-to-uridine RNA-editing events in plant mitochondria and plastids are pentatricopeptide repeat (PPR)-containing proteins with specific additional C-terminal domains. Here we report the related PPR proteins mitochondrial editing factor 8 (MEF8) and MEF8S with only five such repeats each to be both involved in RNA editing at the same two sites in mitochondria of Arabidopsis thaliana. Mutants of MEF8 show diminished editing in leaves but not in pollen, whereas mutants of the related protein MEF8S show reduced RNA editing in pollen but not in leaves. Overexpressed MEF8 or MEF8S both increase editing at the two target sites in a mef8 mutant. Double mutants of MEF8 and MEF8S are not viable although both identified target sites are in mRNAs for nonessential proteins. This suggests that MEF8 and MEF8S may have other essential functions beyond these two editing sites in complex I mRNAs.     

A Case of Gene Fragmentation in Plant Mitochondria Fixed by the Selection of a Compensatory Restorer of Fertility-Like PPR Gene

The high mutational load of mitochondrial genomes combined with their uniparental inheritance and high polyploidy favors the maintenance of deleterious mutations within populations. How cells compose and adapt to the accumulation of disadvantageous mitochondrial alleles remains unclear. Most harmful changes are likely corrected by purifying selection, however, the intimate collaboration between mitochondria- and nuclear-encoded gene products offers theoretical potential for compensatory adaptive changes. In plants, cytoplasmic male sterilities are known examples of nucleo-mitochondrial coadaptation situations in which nuclear-encoded restorer of fertility (Rf) genes evolve to counteract the effect of mitochondria-encoded cytoplasmic male sterility (CMS) genes and restore fertility. Most cloned Rfs belong to a small monophyletic group, comprising 26 pentatricopeptide repeat genes in Arabidopsis, called Rf-like (RFL). In this analysis, we explored the functional diversity of RFL genes in Arabidopsis and found that the RFL8 gene is not related to CMS suppression but essential for plant embryo development. In vitro-rescued rfl8 plantlets are deficient in the production of the mitochondrial heme–lyase complex. A complete ensemble of molecular and genetic analyses allowed us to demonstrate that the RFL8 gene has been selected to permit the translation of the mitochondrial ccmF_N2 gene encoding a heme–lyase complex subunit which derives from the split of the ccmF_N gene, specifically in Brassicaceae plants. This study represents thus a clear case of nuclear compensation to a lineage-specific mitochondrial genomic rearrangement in plants and demonstrates that RFL genes can be selected in response to other mitochondrial deviancies than CMS suppression.     

Properties of the C-terminal Tail of Human Mitochondrial Inner Membrane Protein Oxa1L and Its Interactions with Mammalian Mitochondrial Ribosomes

In humans the mitochondrial inner membrane protein Oxa1L is involved in the biogenesis of membrane proteins and facilitates the insertion of both mitochondrial- and nuclear-encoded proteins from the mitochondrial matrix into the inner membrane. The C-terminal ∼100-amino acid tail of Oxa1L (Oxa1L-CTT) binds to mitochondrial ribosomes and plays a role in the co-translational insertion of mitochondria-synthesized proteins into the inner membrane. Contrary to suggestions made for yeast Oxa1p, our results indicate that the C-terminal tail of human Oxa1L does not form a coiled-coil helical structure in solution. The Oxa1L-CTT exists primarily as a monomer in solution but forms dimers and tetramers at high salt concentrations. The binding of Oxa1L-CTT to mitochondrial ribosomes is an enthalpy-driven process with a K_d of 0.3–0.8 μm and a stoichiometry of 2. Oxa1L-CTT cross-links to mammalian mitochondrial homologs of the bacterial ribosomal proteins L13, L20, and L28 and to mammalian mitochondrial specific ribosomal proteins MRPL48, MRPL49, and MRPL51. Oxa1L-CTT does not cross-link to proteins decorating the conventional exit tunnel of the bacterial large ribosomal subunit (L22, L23, L24, and L29).     

A Combined N-terminomics and Shotgun Proteomics Approach to Investigate the Responses of Human Cells to Rapamycin and Zinc at the Mitochondrial Level

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Highlights

• •Rapamycin and zinc induce moderate but significant mitochondrial proteome changes.
• •The mitochondrial proteins processing system is robust under subtoxic conditions.
• •Rapamycin and zinc perturb the mitochondrial proteins processing system.
• •Rapamycin and zinc perturb the mitochondrial proteins homeostasis.

     

LETM Proteins Play a Role in the Accumulation of Mitochondrially Encoded Proteins in Arabidopsis thaliana and AtLETM2 Displays Parent of Origin Effects

The Arabidopsis thaliana genome contains two genes with homology to the mitochondrial protein LETM1 (leucine zipper-EF-hand-containing transmembrane protein). Inactivation of both genes, Atletm1 and Atletm2, together is lethal. Plants that are hemizygous for AtLETM2 and homozygous for Atletm1 (letm1(−/−) LETM2(+/−)) displayed a mild retarded growth phenotype during early seedling growth. It was shown that accumulation of mitochondrial proteins was reduced in hemizygous (letm1(−/−) LETM2(+/−)) plants. Examination of respiratory chain proteins by Western blotting, blue native PAGE, and enzymatic activity assays revealed that the steady state level of ATP synthase was reduced in abundance, whereas the steady state levels of other respiratory chain proteins remained unchanged. The absence of a functional maternal AtLETM2 allele in an Atletm1 mutant background resulted in early seed abortion. Reciprocal crosses revealed that maternally, but not paternally, derived AtLETM2 was absolutely required for seed development. This requirement for a functional maternal allele of AtLETM2 was confirmed using direct sequencing of reciprocal crosses of Col-0 and Ler accessions. Furthermore, AtLETM2 promoter β-glucuronidase constructs displayed exclusive maternal expression patterns.     

Quantitative Proteomics of the Mitotic Chromosome Scaffold Reveals the Association of BAZ1B with Chromosomal Axes,

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Highlights

• •Quantitative proteomics of mitotic chromosome scaffold isolated from chicken DT40 cells.
• •BAZ1B identified in the isolated mitotic chromosome scaffold localizes to mitotic chromosome axes.
• •BAZ1B knockout caused prophase delay because of altered chromosome condensation timing and impaired mitosis progression.
• •BAZ1B knockout did not affect prometaphase chromosome structure.

     

干旱胁迫对3种不同光合类型荒漠植物叶绿体和线粒体超微结构的影响

以荒漠木本C_3植物天山猪毛菜、C_3-C_4中间型植物松叶猪毛菜、C_4植物木本猪毛菜为研究对象,采用盆栽控水试验,设置正常供水和轻度、中度和重度干旱处理(土壤含水量分别为田间持水量的80%、60%、45%和35%),研究不同程度干旱胁迫对3种不同光合类型荒漠植物叶片超微结构的影响。结果表明:(1)正常水分条件下,叶肉细胞中各细胞器结构完整。(2)轻度干旱胁迫下,3种植物叶片超微结构未受损伤,无明显变化。(3)中度干旱胁迫下,天山猪毛菜和松叶猪毛菜叶肉细胞壁界限不清晰,类囊体片层扩张且排列不紧密,不同之处在于,天山猪毛菜线粒体最先出现降解,内含物流失,而松叶猪毛菜线粒体外膜轮廓变形,嵴减少;木本猪毛菜线粒体无明显变化,叶绿体轻微扩张。(4)重度干旱胁迫下,天山猪毛菜和松叶猪毛菜叶绿体受损且结构混乱,线粒体出现降解;木本猪毛菜叶绿体出现膨胀,线粒体外膜轮廓模糊,嵴减少且结构模糊不清楚。研究认为,不同程度干旱胁迫下木本猪毛菜叶绿体和线粒体的受损程度都最低;干旱胁迫下天山猪毛菜和松叶猪毛菜叶绿体的受损程度大致相似;松叶猪毛菜和木本猪毛菜线粒体对干旱胁迫的耐受力要比叶绿体强。     

HIGD2A is Required for Assembly of the COX3 Module of Human Mitochondrial Complex IV

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Highlights

• •Quantitative proteomics reveals HIGD2A is required for assembly of the COX3 module.
• •Pulse-SILAC demonstrates that HIGD2A is involved in COX3 biogenesis.
• •Supercomplexes in HIGD2A knockout cells are depleted of COX3.
• •HIGD2A is the first assembly factor identified for the COX3 module of Complex IV.

     

Novel Proteomic Profiling of Epididymal Extracellular Vesicles in the Domestic Cat Reveals Proteins Related to Sequential Sperm Maturation with Differences Observed between Normospermic and Teratospermic Individuals

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Highlights

• •Several proteins were found to be unique to each male type.
• •Expression levels of seven proteins trended downward in teratospermic males.
• •Several proteins were related to sperm motility and subsequent oocyte binding.

     

Hepatic Mitochondrial Defects in a Nonalcoholic Fatty Liver Disease Mouse Model Are Associated with Increased Degradation of Oxidative Phosphorylation Subunits

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Highlights

• •Stability of oxidative phosphorylation subunits are reduced in a diet-induced mouse model of NAFLD.
• •These changes are associated with impaired activities of electron transport chain complexes and ATP synthesis.
• •Increased mitophagy contributed to enhanced degradation of mitochondrial proteins.

     

The Secretome Profiling of a Pediatric Airway Epithelium Infected with hRSV Identified Aberrant Apical/Basolateral Trafficking and Novel Immune Modulating (CXCL6, CXCL16, CSF3) and Antiviral (CEACAM1) Proteins

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Highlights

• •Proteome of airway secretions derived from mock- and hRSV-infected WD-PBEC cultures.
• •A polarised secretome in uninfected WD-PBECs, skewed in hRSV-infected cultures.
• •CXCL6, CXCL16, CECACAM1 and CSF3 induced only upon hRSV-infection.
• •Detection of CXCL6, CXCL16 and CSF3 in NPAs from hRSV-positive children.

     

Characterizing Patients with Recurrent Urinary Tract Infections in Vesicoureteral Reflux: A Pilot Study of the Urinary Proteome

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Highlights

• •Urinary proteomes of patients with recurrent UTI, renal scarring, and VUR.
• •80 proteins differentially expressed, compared to healthy controls.
• •62 proteins may be indicative of susceptibility for UTI.
• •Altered acute phase response, extracellular matrix and carbohydrate metabolism.

     

Analysis of the Solvent Accessibility of Cysteine Residues on Maize rayado fino virus Virus-like Particles Produced in Nicotiana benthamiana Plants and Cross-linking of Peptides to VLPs

Mimicking and exploiting virus properties and physicochemical and physical characteristics holds promise to provide solutions to some of the world''s most pressing challenges. The sheer range and types of viruses coupled with their intriguing properties potentially give endless opportunities for applications in virus-based technologies. Viruses have the ability to self- assemble into particles with discrete shape and size, specificity of symmetry, polyvalence, and stable properties under a wide range of temperature and pH conditions. Not surprisingly, with such a remarkable range of properties, viruses are proposed for use in biomaterials ⁹, vaccines ^{14, 15}, electronic materials, chemical tools, and molecular electronic containers^{4, 5, 10, 11, 16, 18, 12}.In order to utilize viruses in nanotechnology, they must be modified from their natural forms to impart new functions. This challenging process can be performed through several mechanisms including genetic modification of the viral genome and chemically attaching foreign or desired molecules to the virus particle reactive groups ⁸. The ability to modify a virus primarily depends upon the physiochemical and physical properties of the virus. In addition, the genetic or physiochemical modifications need to be performed without adversely affecting the virus native structure and virus function. Maize rayado fino virus (MRFV) coat proteins self-assemble in Escherichia coli producing stable and empty VLPs that are stabilized by protein-protein interactions and that can be used in virus-based technologies applications ⁸. VLPs produced in tobacco plants were examined as a scaffold on which a variety of peptides can be covalently displayed ¹³. Here, we describe the steps to 1) determine which of the solvent-accessible cysteines in a virus capsid are available for modification, and 2) bioconjugate peptides to the modified capsids. By using native or mutationally-inserted amino acid residues and standard coupling technologies, a wide variety of materials have been displayed on the surface of plant viruses such as, Brome mosaic virus ³, Carnation mottle virus ¹², Cowpea chlorotic mottle virus ⁶, Tobacco mosaic virus ¹⁷, Turnip yellow mosaic virus ¹, and MRFV ¹³.