Determining the temperature acclimation capacity of Australian rainforest trees growing in warm and cool climates

The effect of climate warming on rainforest trees, including temperate, subtropical and tropical rainforests is poorly understood. Tropical rainforest tree species are particularly threatened by climate warming and may experience a decline of growth in the future, which would be a major problem given their importance in the global carbon budget and in regulating global climate. Hence, we need to predict the response of rainforests in a future warmer world. To make such projections, we need to quantify the physiological and ecological responses of rainforest tree species to warming, particularly in tropical species, and determine their physiological thermal limits. My broad goal in this thesis is to investigate the mechanisms underpinning the various physiological responses by which rainforest tree species from different latitudes adjust to warming, including heatwaves. Overall, this thesis provides a mechanistic understanding of the physiological processes that change in response to warming in rainforest tree species from different biomes. Tropical tree species can clearly cope with less warming compared to temperate tree species. This has implications for predicting rainforest responses to warming along a latitudinal gradient, including potentially reduced carbon uptake in tropical ecosystems in a future, warmer world

Gene expression studies in isolated mitochondria: Solanum tuberosum rps10 is recognized by cognate potato but not by the transcription, splicing and editing machinery of wheat mitochondria

The complex gene expression mechanisms that occur in plant mitochondria, such as RNA editing and splicing, are not yet well understood. RNA editing in higher plant mitochondria is a highly specific process which modifies mRNA sequences by C-to-U conversions. It has been suggested that in some cases this process is required for splicing. Here, we use an experimental model based on the introduction of DNA into isolated mitochondria by electroporation to study organellar gene expression events. Our aim was to compare processing and editing of potato small ribosomal protein 10 gene (rps10) transcripts in heterologous (wheat mitochondria) and homologous (potato mitochondria) contexts. rps10 is a suitable model because it contains a group II intron, is absent in wheat mitochondria but is actively expressed in potato mitochondria, where transcripts are spliced and undergo five C-to-U editing events. For this purpose, conditions for electroporating isolated potato mitochondria were established. rps10 was placed under the control of either potato or wheat cox2 promoters. We found that rps10 was only transcribed under the control of a cognate promoter. In wheat mitochondria, rps10 transcripts were neither spliced nor edited while they are correctly processed in potato mitochondria. Interestingly, a wheat editing site grafted into rps10 was not recognized by wheat mitochondria but was correctly edited in potato mitochondria. Taken together, these results suggest that editing might occur only when the transcripts are engaged in processing and that they would not be available to editing factors outside of a putative RNA maturation machinery complex

Intron RNA editing is essential for splicing in plant mitochondria

Most plant mitochondria messenger RNAs (mRNAs) undergo editing through C-to-U conversions located mainly in exon sequences. However, some RNA editing events are found in non-coding regions at critical positions in the predicted secondary and tertiary structures of introns, suggesting that RNA editing could be important for splicing. Here, we studied the relationships between editing and splicing of the mRNA encoding the ribosomal protein S10 (rps10), which has a group II intron and five editing sites. Two of them, C2 and C3, predicted to stabilize the folded structure of the intron necessary for splicing, were studied by using rps10 mutants introduced into isolated potato mitochondria by electroporation. While mutations of C2 involved in EBS2/IBS2 interactions did not affect splicing, probably by the presence of an alternative EBS2′ region in domain I of the intron, the edition of site C3 turned out to be critical for rps10 mRNA splicing; only the edited (U) form of the transcript was processed. Interestingly, RNA editing was strongly reduced in transcripts from two different intronless genes, rps10 from potato and cox2 from wheat, suggesting that efficient RNA processing may require a close interaction of factors engaged in different maturation processes. This is the first report linking editing and splicing in conditions close to the in vivo situation

Intron RNA editing is essential for splicing in plant mitochondria

Most plant mitochondria messenger RNAs (mRNAs) undergo editing through C-to-U conversions located mainly in exon sequences. However, some RNA editing events are found in non-coding regions at critical positions in the predicted secondary and tertiary structures of introns, suggesting that RNA editing could be important for splicing. Here, we studied the relationships between editing and splicing of the mRNA encoding the ribosomal protein S10 (rps10), which has a group II intron and five editing sites. Two of them, C2 and C3, predicted to stabilize the folded structure of the intron necessary for splicing, were studied by using rps10 mutants introduced into isolated potato mitochondria by electroporation. While mutations of C2 involved in EBS2/IBS2 interactions did not affect splicing, probably by the presence of an alternative EBS2 0 region in domain I of the intron, the edition of site C3 turned out to be critical for rps10 mRNA splicing; only the edited (U) form of the transcript was processed. Interestingly, RNA editing was strongly reduced in transcripts from two different intronless genes, rps10 from potato and cox2 from wheat, suggesting that efficient RNA processing may require a close interaction of factors engaged in different maturation processes. This is the first report linking editing and splicing in conditions close to the in vivo situation

The RNA Editing Pattern of cox2 mRNA Is Affected by Point Mutations in Plant Mitochondria

The mitochondrial transcriptome from land plants undergoes hundreds of specific C-to-U changes by RNA editing. These events are important since most of them occur in the coding region of mRNAs. One challenging question is to understand the mechanism of recognition of a selected C residue (editing sites) on the transcript. It has been reported that a short region surrounding the target C forms the cis-recognition elements, but individual residues on it do not play similar roles for the different editing sites. Here, we studied the role of the −1 and +1 nucleotide in wheat cox2 editing site recognition using an in organello approach. We found that four different recognition patterns can be distinguished: (a) +1 dependency, (b) −1 dependency, (c) +1/−1 dependency, and (d) no dependency on nearest neighbor residues. A striking observation was that whereas a 23 nt cis region is necessary for editing, some mutants affect the editing efficiency of unmodified distant sites. As a rule, mutations or pre-edited variants of the transcript have an impact on the complete set of editing targets. When some Cs were changed into Us, the remaining editing sites presented a higher efficiency of C-to-U conversion than in wild type mRNA. Our data suggest that the complex response observed for cox2 mRNA may be a consequence of the fate of the transcript during mitochondrial gene expression

Synthèse d’hétérocycles mixtes soufrés et azotés de taille moyenne par des réactions métallo-catalysées

The aim of this thesis was to develop new metal-catalyzed reactions allowing access to original mixed sulfur and nitrogen medium-sized heterocycles of original, containing several stereogenic centers. The strategy was based on an intramolecular C-N or C-S bond formation from 1,3-aminothioethers precursors, with suitable functionalization on heteroatoms, depending on the type of cyclization and on the metal envisaged.First, a copper-catalyzed intramolecular N-arylation reaction was developed from 1,3-aminothioethers containing iodobenzene attached to the sulfur atom. This coupling allowed the synthesis of a new family of benzothiazocines containing two or three stereogenic centers on the eight-membered heterocycle.The second method developed involed a gold-catalyzed intramolecular carbothiolation of a triple bond. Starting from S-allyl N-propargyl 1,3-aminothioethers, this reaction gave access to a variety of thiazepines containing two or three stereogenic centers on the seven-membered heterocycle. In addition, from the N-propargylated thiazepines obtained, a gold-catalyzed cycloisomerization of 1,6-enynes led to original bridged polycyclic structures.L’objectif de cette thèse a été de développer de nouvelles réactions métallo-catalysées permettant d’accéder à des hétérocycles mixtes soufrés et azotés de taille moyenne originaux, comportant plusieurs centres stéréogènes. La stratégie a été basée sur la formation intramoléculaire d'une liaison C-N ou C-S à partir de précurseurs 1,3-aminothioéthers dont la fonctionnalisation des hétéroatomes a été adaptée au type de cyclisation et au métal envisagés.Dans un premier temps, une réaction de N-arylation intramoléculaire catalysée au cuivre a été développée à partir de 1,3-aminothioéthers contenant un iodobenzène lié à l’atome de soufre. Ce couplage a permis de synthétiser une nouvelle famille de benzothiazocines comportant deux ou trois centres stéréogènes sur l’hétérocycle à huit chaînons.La deuxième méthode développée a consisté en une carbothiolation intramoléculaire d'une triple liaison catalysée à l’or. A partir de S-allyle N-propargyle 1,3-aminothioéthers, cette réaction a donné accès à une variété de thiazépines comportant deux ou trois centres stéréogènes sur l’hétérocycle à sept chaînons. De plus, à partir des thiazépines N-propargylées obtenues, une cycloisomérisation d’énynes-1,6 catalysée à l’or a conduit à des structures polycycliques pontés originales

Synthesis of medium-sized N,S-heterocycles by metal-catalyzed reactions

L’objectif de cette thèse a été de développer de nouvelles réactions métallo-catalysées permettant d’accéder à des hétérocycles mixtes soufrés et azotés de taille moyenne originaux, comportant plusieurs centres stéréogènes. La stratégie a été basée sur la formation intramoléculaire d'une liaison C-N ou C-S à partir de précurseurs 1,3-aminothioéthers dont la fonctionnalisation des hétéroatomes a été adaptée au type de cyclisation et au métal envisagés.Dans un premier temps, une réaction de N-arylation intramoléculaire catalysée au cuivre a été développée à partir de 1,3-aminothioéthers contenant un iodobenzène lié à l’atome de soufre. Ce couplage a permis de synthétiser une nouvelle famille de benzothiazocines comportant deux ou trois centres stéréogènes sur l’hétérocycle à huit chaînons.La deuxième méthode développée a consisté en une carbothiolation intramoléculaire d'une triple liaison catalysée à l’or. A partir de S-allyle N-propargyle 1,3-aminothioéthers, cette réaction a donné accès à une variété de thiazépines comportant deux ou trois centres stéréogènes sur l’hétérocycle à sept chaînons. De plus, à partir des thiazépines N-propargylées obtenues, une cycloisomérisation d’énynes-1,6 catalysée à l’or a conduit à des structures polycycliques pontés originales.The aim of this thesis was to develop new metal-catalyzed reactions allowing access to original mixed sulfur and nitrogen medium-sized heterocycles of original, containing several stereogenic centers. The strategy was based on an intramolecular C-N or C-S bond formation from 1,3-aminothioethers precursors, with suitable functionalization on heteroatoms, depending on the type of cyclization and on the metal envisaged.First, a copper-catalyzed intramolecular N-arylation reaction was developed from 1,3-aminothioethers containing iodobenzene attached to the sulfur atom. This coupling allowed the synthesis of a new family of benzothiazocines containing two or three stereogenic centers on the eight-membered heterocycle.The second method developed involed a gold-catalyzed intramolecular carbothiolation of a triple bond. Starting from S-allyl N-propargyl 1,3-aminothioethers, this reaction gave access to a variety of thiazepines containing two or three stereogenic centers on the seven-membered heterocycle. In addition, from the N-propargylated thiazepines obtained, a gold-catalyzed cycloisomerization of 1,6-enynes led to original bridged polycyclic structures

Etude de l'édition des ARN mitochondriaux de plantes supèrieures (éléments de reconnaissance en cis et relation avec les autres processus de maturation)

Le travail présenté décrit les éléments en cis requis pour la reconnaissance des sites d'édition dans les plantes supérieures. Pour deux sites, nous avons confirmé qu'une région de 23 nucléotides est nécessaire pour l'édition. Ces régions ne possèdent pas de séquence consensus. Ainsi, bien que les éléments en cis aient une taille identique et une même localisation, les mécanismes de reconnaissance peuvent différer. Ces observations constituent un argument selon lequel les sites sont reconnus par des facteurs trans différents. Nous avons montré, paar électroporation avec des gènes issus de deux espèces, que des sites peuvent être reconnus dans un contexte hétérologue. Les facteurs trans de ces sites sont donc, soit conservés après la perte du site cible, soit communs à d'autres sites. L'ARN rps 10 de pomme de terre n'est pas reconnu dans le blé. Cela indique qu'il y existerait un point de contrôle permettant d'engager ou non l'ARN dans les voies de maturation.This work describes the cis-recognition elements required for RNA editing in higher plants. We confirm for two editing sites that a minimal region of 23 nucleotides was necessary for editing. Studies of this region indicated that they are not consensus sequences. Suggesting that, notwithstanding a similar extent and location of cis-elements, the editing site recognition mechanisms may differ in plant mitochondria. This is an argument that both sites are recognized by different trans-acting factors. Chimeric constructs from either potatoe or wheat were used in electroporation experiments. We found that some editing sites were recognized in the heterologous context suggesting that those sites the putative trans-acting factors were conserved after the lost of the editing substrate or may recognize different sites. In wheat mitochondria, the potatoe rps 10 RNA was not recognized by wheat mitochondria. These results suggest the existence of a check point in the RNA maturation machinery.BORDEAUX2-BU Santé (330632101) / SudocSudocFranceF