An mTRAN-mRNA interaction mediates mitochondrial translation initiation in plants

Plant mitochondria represent the largest group of respiring organelles on the planet. Plant mitochondrial messenger RNAs (mRNAs) lack Shine-Dalgarno-like ribosome-binding sites, so it is unknown how plant mitoribosomes recognize mRNA. We show that “mitochondrial translation factors” mTRAN1 and mTRAN2 are land plant–specific proteins, required for normal mitochondrial respiration chain biogenesis. Our studies suggest that mTRANs are noncanonical pentatricopeptide repeat (PPR)–like RNA binding proteins of the mitoribosomal “small” subunit. We identified conserved Adenosine (A)/Uridine (U)-rich motifs in the 5′ regions of plant mitochondrial mRNAs. mTRAN1 binds this motif, suggesting that it is a mitoribosome homing factor to identify mRNAs. We demonstrate that mTRANs are likely required for translation of all plant mitochondrial mRNAs. Plant mitochondrial translation initiation thus appears to use a protein-mRNA interaction that is divergent from bacteria or mammalian mitochondria

Diversité fonctionnelle au sein d'une famille de protéines de type ribosomique chez Arabidopsis thaliana

L'expression des ARN mitochondriaux et chloroplastiques des plantes implique un grand nombre de modifications post-transcriptionnelles, parmi lesquelles l'épissage des introns est un processus essentiel. Sur la base de leur structure et des mécanismes d'épissage associés, les introns peuvent être classés en deux familles et ceux présents dans les organites des plantes appartiennent au groupe II. Les introns mitochondriaux et chloroplastiques de groupe II sont fortement dégénérés et ont perdu la capacité de s'auto-épisser in vivo. Leur élimination nécessite l’action de nombreux facteurs protéiques codés dans le noyau et importés dans les organites. Les protéines de liaison à l'ARN jouent un rôle prédominant dans ce processus complexe. Les protéines ribosomales sont des protéines abondantes se liant à l'ARN et peuvent être recrutées pour remplir diverses fonctions annexes. Au cours de ma thèse, j’ai étudié la fonction des protéines de type uL18 chez Arabidopsis, qui comprend 8 membres. Ces protéines partagent un domaine uL18 plutôt dégénéré, mais dont la structure est conservée, et dont la fonction initiale est de permettre l’association avec l’ARNr 5S. Nos résultats ont montré que cinq protéines de type uL18 sont adressées aux mitochondries et trois aux chloroplastes. Deux d’entre elles correspondent à de véritables protéines ribosomales uL18 associées aux ribosomes des organites, tandis que deux autres (uL18-L1 et uL18-L8) se sont transformées en facteurs d'épissage et sont nécessaires à l'élimination d’introns mitochondriaux ou chloroplastiques spécifiques. L'analyse d'un troisième membre de la famille, uL18-L5, a révélé qu'il participait à l'épissage de nombreux introns mitochondriaux. Mes résultats ont permis de révéler que les facteurs dérivés des protéines ribosomales uL18 jouent un rôle essentiel dans l’épissage des introns du groupe II mitochondriaux ou chloroplastiques chez les végétaux et que ces fonctions ciblent sot un seul intron ou bien plusieurs d’entre eux.RNA expression in plant organelles implies a large number of post-transcriptional modifications in which intron splicing is an essential process. Based on RNA structures and splicing mechanisms, introns can be classified into two families and organellar introns of seed plants are categorized as group II. Organellar group II introns are highly degenerate and have lost the ability to self-splice in vivo. Their removal from transcripts is thus facilitated by numerous nuclear-encoded proteins that are post-translationaly imported into organelles. Among them, RNA binding proteins play predominant roles in this complex process. Ribosomal proteins are abundant RNA-binding proteins and could be recruited to carry out multifarious auxiliary functions. During my thesis, I investigated the function of the uL18 ribosomal-like protein family in Arabidopsis that comprises 8 members. The members of this protein family share a rather degenerate but structurally conserved uL18 domain whose original function is to permit association with the 5S rRNA. Our results showed that five uL18-Like proteins are targeted to mitochondria and three to chloroplasts. Two of these proteins correspond to real ribosomal uL18 proteins that incorporate into organellar ribosomes, while two other members (uL18-L1 and uL18-L8) have turned into splicing factors and are required for the removal of specific mitochondrial or plastid group II introns. The analysis of a third member, uL18-L5, revealed that it participated in the splicing of numerous mitochondrial introns. Our results revealed that uL18-like factors play essential roles in group II intron splicing in both mitochondria and plastids of plants and that these functions could target a single or multiple introns

Three new pentatricopeptide repeat proteins facilitate the splicing of mitochondrial transcripts and complex I biogenesis in Arabidopsis

Group II introns are common features of most angiosperm mitochondrial genomes. Intron splicing is thus essential for the expression of mitochondrial genes and is facilitated by numerous nuclear-encoded proteins. However, the molecular mechanism and the protein cofactors involved in this complex process have not been fully elucidated. In this study, we characterized three new pentatricopeptide repeat (PPR) genes, called MISF26, MISF68, and MISF74, of Arabidopsis and showed they all function in group II intron splicing and plant development. The three PPR genes encode P-type PPR proteins that localize in the mitochondrion. Transcript analysis revealed that the splicing of a single intron is altered in misf26 mutants, while several mitochondrial intron splicing defects were detected in misf68 and misf74 mutants. To our knowledge, MISF68 and MISF74 are the first two PPR proteins implicated in the splicing of more than one intron in plant mitochondria, suggesting that they may facilitate splicing differently from other previously identified PPR splicing factors. The splicing defects in the misf mutants induce a significant decrease in complex I assembly and activity, and an overexpression of mRNAs of the alternative respiratory pathway. These results therefore reveal that nuclear encoded proteins MISF26, MISF68, and MISF74 are involved in splicing of a cohort of mitochondria! group II introns and thereby required for complex I biogenesis

The complete mitochondrial genome and phylogenetic analysis of Tipula (Yamatotipula) nova Walker, 1848 (Diptera, Tipulidae) from Qingdao, Shandong, China

The genus Tipula Linnaeus, is a large group of crane flies with more than 2400 known species from 41 subgenera. In this study, we report the first complete mitochondrial (mt) genome sequence of the subgenus Tipula (Yamatotipula), which is a circular molecule of 15,668 bp with an AT content of 77.2%. The mt genome contains 13 protein-coding genes, 22 tRNA genes, 2 rRNA genes, and a long non-coding region. Three conserved overlapping regions, 8 bp between tRNATrp and tRNACys, 7 bp between ATP8 and ATP6, and 7 bp between ND4 and ND4L, are found. Phylogenetic analysis reveals that the Tipulomorpha includes the family Trichoceridae and the Trichoceridae is sister-group to the remaining Tipulomorpha

Sn promoted BaFeO3-delta catalysts for N2O decomposition: Optimization of CrossMark Fe active centers

A series of BaFe1-xSnxO3-delta catalysts were prepared by sol-gel method and tested for N2O decomposition to shed light on the effect of B-site substitution on the catalytic behavior of perovskite catalysts. Sn-119 and Fe-57 Mossbauer results confirmed that the 5-fold coordinated Fe3+ cations with one adjacent oxygen vacancy (Fe3+-O-5) were the main active centers for N2O decomposition. Doping of Sn cations can significantly improve the percentage of Fe3+-O-5 from 30% (x = 0) to 68% (x = 0.8). More importantly, the valence state of Fe could be gradually reduced due to weakening of Fe-O bond with increasing the Sn content, which was attributed to the stronger force of Sn than Fe in Fe-O Sn structure to draw the oxygen anion and expansion of unit cell volume. Such change of Fe chemical state favored the oxygen mobility of the catalyst, leading to reduction in activation energy for N2O decomposition from ca. 241 (x = 0) to 178 kJ moL(-1) (x = 0.8). BaFe0.2Sn0.8O3-delta,5 catalyst exhibited the highest intrinsic rate of 1.49 s(-1) (550 degrees C), nearly 4 times larger than that of BaFeO3-delta (0.43 s(-1)). (C) 2017 Elsevier Inc. All rights reserved

A molten carbonate shell modified perovskite redox catalyst for anaerobic oxidative dehydrogenation of ethane

Acceptor-doped, redox-active perovskite oxides such as La0.8Sr0.2FeO3 (LSF) are active for ethane oxidation to CO X but show poor selectivity to ethylene. This article reports molten Li2CO3 as an effective "promoter" to modify LSF for chemical looping-oxidative dehydrogenation (CL-ODH) of ethane. Under the working state, the redox catalyst is composed of a molten Li2CO3 layer covering the solid LSF substrate. The molten layer facilitates the transport of active peroxide (O-2(2-)) species formed on LSF while blocking the nonselective sites. Spectroscopy measurements and density functional theory calculations indicate that Fe4+ -> Fe3+ transition is responsible for the peroxide formation, which results in both exothermic ODH and air reoxidation steps. With >90% ethylene selectivity, up to 59% ethylene yield, and favorable heat of reactions, the core-shell redox catalyst has an excellent potential to be effective for intensified ethane conversion. The mechanistic findings also provide a generalized approach for designing CL-ODH redox catalysts

Preparation of BaSnO3 and Ba(0.9)6La(0.04)SnO(3) by reactive core-shell precursor: formation process, CO sensitivity, electronic and optical properties analysis

We propose a facile and economic strategy for preparing BaSnO3 particles from a room-temperature fabricated BaCO3@SnO2 core-shell precursor. The core-shell structure promoted the mixing degree of the reactants and effectively suppressed sintering of the particles, therefore, pure BaSnO3 was obtained at 800 degrees C, nearly 400 degrees C lower than traditional solid-state reaction (SSR) method, and showed better CO sensitivity than BaSnO3 prepared by SSR route. The phase transformation, morphology changes, and structure evolution from the precursor to the final BaSnO3 were systematically investigated, and a clear picture of the formation mechanism of BaSnO3 was given. Slightly La doped BaSnO3 was prepared through the same procedure as BaSnO3, which proved the availability of this method for synthesis of slightly doped BaSnO3 materials. The optical properties and total conductivity of pure and La doped BaSnO3 were compared. The results showed that the band gap of the La-doped sample was slightly increased, while the resistivity was more than six orders of magnitude lower than that of pure BaSnO3. The underlying reason was studied for the first time by directly monitoring the electron structure of Sn cations at the atomic scale using Sn-119 Mossbauer spectroscopy. It was found that the introduction of La in BaSnO3 solid solution would induce electron donating to the 5s orbital of Sn4+, and Sn cations were slightly reduced. This result gave clear evidence of conduction band filling in La-doped BaSnO3, which accounted for the change in the electric and optical properties