Papers by Christophe Laloi
Plant Journal, Dec 1, 2006
Vitamin B6 is an essential coenzyme for numerous metabolic enzymes and is a potent antioxidant. I... more Vitamin B6 is an essential coenzyme for numerous metabolic enzymes and is a potent antioxidant. In plants, very little is known about its contribution to viability, growth and development. The de novo pathway of vitamin B6 biosynthesis has only been described recently and involves the protein PDX1 (pyridoxal phosphate synthase protein). Arabidopsis thaliana has three homologs of PDX1, two of which, PDX1.1 and PDX1.3, have been demonstrated as functional in vitamin B6 biosynthesis in vitro and by yeast complementation. In this study, we show that the spatial and temporal expression patterns of PDX1.1 and PDX1.3, investigated at the transcript and protein level, largely overlap, but PDX1.3 is more abundant than PDX1.1. Development of single pdx1.1 and pdx1.3 mutants is partially affected, whereas disruption of both genes causes embryo lethality at the globular stage. Detailed examination of the single mutants, in addition to those that only have a single functional copy of either gene, indicates that although these genes are partially redundant in vitamin B6 synthesis, PDX1.3 is more requisite than PDX1.1. Developmental distinctions correlate with the vitamin B6 content. Furthermore, we provide evidence that in addition to being essential for plant growth and development, vitamin B6 also plays a role in stress tolerance and photoprotection of plants.
Proceedings of the National Academy of Sciences of the United States of America, Jun 27, 2022
The organization of the genome into transcriptionally active and inactive chromatin domains requi... more The organization of the genome into transcriptionally active and inactive chromatin domains requires well-delineated chromatin boundaries and insulator functions in order to maintain the identity of adjacent genomic loci with antagonistic chromatin marks and functionality. In plants that lack known chromatin insulators, the mechanisms that prevent heterochromatin spreading into euchromatin remain to be identified. Here, we show that DNA Topoisomerase VI participates in a chromatin boundary function that safeguards the expression of genes in euchromatin islands within silenced heterochromatin regions. While some transposable elements are reactivated in mutants of the Topoisomerase VI complex, genes insulated in euchromatin islands within heterochromatic regions of the Arabidopsis thaliana genome are specifically down-regulated. H3K9me2 levels consistently increase at euchromatin island loci and decrease at some transposable element loci. We further show that Topoisomerase VI physically interacts with S-adenosylmethionine synthase methionine adenosyl transferase 3 (MAT3), which is required for H3K9me2. A Topoisomerase VI defect affects MAT3 occupancy on heterochromatic elements and its exclusion from euchromatic islands, thereby providing a possible mechanistic explanation to the essential role of Topoisomerase VI in the delimitation of chromatin domains.
Plant Journal, Oct 1, 2009
Shortly after the release of singlet oxygen ((1)O(2)) in chloroplasts, changes in nuclear gene ex... more Shortly after the release of singlet oxygen ((1)O(2)) in chloroplasts, changes in nuclear gene expression occur in the conditional flu mutant of Arabidopsis that reveal a rapid transfer of signals from the plastid to the nucleus. Extensive genetic screens aimed at identifying constituents involved in (1)O(2)-mediated plastid-to-nucleus signaling have failed to identify extraplastidic signaling components. This finding suggests that (1)O(2)-mediated signals are not translocated to the nucleus via a single linear pathway, but rather through a signaling network that is difficult to block by single mutations. The complexity of this signaling network has been tackled by mutagenizing a transgenic flu line expressing the luciferase reporter gene under the control of the promoter of a (1)O(2)-responsive AAA-ATPase gene (At3g28580) and isolating second site mutants that constitutively express the reporter gene at a high level. One of the mutants was shown by map-based cloning and sequencing to contain a single amino acid change in the PLEIOTROPIC RESPONSE LOCUS 1 (PRL1) protein. PRL1 suppresses the expression of AAA-ATPase and other (1)O(2)-responsive genes. PRL1 seems to play a major role in modulating responses of plants to environmental changes by interconnecting (1)O(2)-mediated retrograde signaling with other signaling pathways.
The Plant Journal, 2006
Vitamin B6 is an essential coenzyme for numerous metabolic enzymes and is a potent antioxidant. I... more Vitamin B6 is an essential coenzyme for numerous metabolic enzymes and is a potent antioxidant. In plants, very little is known about its contribution to viability, growth and development. The de novo pathway of vitamin B6 biosynthesis has only been described recently and involves the protein PDX1 (pyridoxal phosphate synthase protein). Arabidopsis thaliana has three homologs of PDX1, two of which, PDX1.1 and PDX1.3, have been demonstrated as functional in vitamin B6 biosynthesis in vitro and by yeast complementation. In this study, we show that the spatial and temporal expression patterns of PDX1.1 and PDX1.3, investigated at the transcript and protein level, largely overlap, but PDX1.3 is more abundant than PDX1.1. Development of single pdx1.1 and pdx1.3 mutants is partially affected, whereas disruption of both genes causes embryo lethality at the globular stage. Detailed examination of the single mutants, in addition to those that only have a single functional copy of either gene, indicates that although these genes are partially redundant in vitamin B6 synthesis, PDX1.3 is more requisite than PDX1.1. Developmental distinctions correlate with the vitamin B6 content. Furthermore, we provide evidence that in addition to being essential for plant growth and development, vitamin B6 also plays a role in stress tolerance and photoprotection of plants.
Biochemical Journal, 2013
Mia40 is a highly conserved mitochondrial protein that plays an essential role in the import and ... more Mia40 is a highly conserved mitochondrial protein that plays an essential role in the import and oxidative folding of many proteins of the mitochondrial intermembrane space. Mia40 uses its redox active CPC motif to shuttle disulfides between its client proteins (newly imported proteins) and the thiol oxidase Erv1. As a thiol oxidoreductase, no cofactor was found in Mia40, nor is a cofactor required for this function. In the present study we, for the first time based on both in vitro and in vivo studies, show that yeast Mia40 can exist as an Fe–S (iron–sulfur) protein as well. We show that Mia40 binds a [2Fe–2S] cluster in a dimer form with the cluster co-ordinated by the cysteine residues of the CPC motifs. The biological relevance of the cofactor binding was confirmed in vivo by cysteine redox state and iron uptake analyses, which showed that a significant amount of cellular Mia40 binds iron in vivo. Furthermore, our oxygen consumption results suggested that the Fe–S-containing Mia...
Proceedings of the National Academy of Sciences of the United States of America, Nov 20, 2001
Plants possess two well described thioredoxin systems: a cytoplasmic system including several thi... more Plants possess two well described thioredoxin systems: a cytoplasmic system including several thioredoxins and an NADPH-dependent thioredoxin reductase and a specific chloroplastic system characterized by a ferredoxin-dependent thioredoxin reductase. On the basis of biochemical activities, plants also are supposed to have a mitochondrial thioredoxin system as described in yeast and mammals, but no gene encoding plant mitochondrial thioredoxin or thioredoxin reductase has been identified yet. We report the characterization of a plant thioredoxin system located in mitochondria. Arabidopsis thaliana genome sequencing has revealed numerous thioredoxin genes among which we have identified AtTRX-o1, a gene encoding a thioredoxin with a potential mitochondrial transit peptide. AtTRX-o1 and a second gene, AtTRX-o2, define, on the basis of the sequence and intron positions, a new thioredoxin type up to now specific to plants. We also have characterized AtNTRA, a gene encoding a protein highly similar to the previously described cytosolic NADPH-dependent thioredoxin reductase AtNTRB but with a putative presequence for import into mitochondria. Western blot analysis of A. thaliana subcellular and submitochondrial fractions and in vitro import experiments show that AtTRX-o1 and AtNTRA are targeted to the mitochondrial matrix through their cleavable N-terminal signal. The two proteins truncated to the estimated mature forms were produced in Escherichia coli; AtTRX-o1 efficiently reduces insulin in the presence of DTT and is reduced efficiently by AtNTRA and NADPH. Therefore, the thioredoxin and the NADPH-dependent thioredoxin reductase described here are proposed to constitute a functional plant mitochondrial thioredoxin system.
Plant Methods
Background The bimolecular fluorescence complementation (BiFC) assay has emerged as one of the mo... more Background The bimolecular fluorescence complementation (BiFC) assay has emerged as one of the most popular methods for analysing protein–protein interactions (PPIs) in plant biology. This includes its increasing use as a tool for dissecting the molecular mechanisms of chloroplast function. However, the construction of chloroplast fusion proteins for BiFC can be difficult, and the availability and selection of appropriate controls is not trivial. Furthermore, the challenges of performing BiFC in restricted cellular compartments has not been specifically addressed. Results Here we describe the development of a flexible modular cloning-based toolkit for BiFC (MoBiFC) and proximity labelling in the chloroplast and other cellular compartments using synthetic biology principles. We used pairs of chloroplast proteins previously shown to interact (HSP21/HSP21 and HSP21/PTAC5) and a negative control (HSP21/ΔPTAC5) to develop standardised Goldengate-compatible modules for the assembly of pro...
SummaryIn plants adverse environmental conditions can induce the accumulation of reactive oxygen ... more SummaryIn plants adverse environmental conditions can induce the accumulation of reactive oxygen species, such as singlet oxygen or hydrogen peroxide, at the level of the photosynthetic apparatus. The coordinated action of nucleus-encoded genes is required for containing the deleterious effects of reactive oxygen species. The regulation of such genes follows a molecular signalling process between the chloroplast and the nucleus called retrograde signalling. Previously, we proposed that the Topoisomerase VI (Topo VI) complex participates in the singlet oxygen stress response by regulating the expression of specific subsets of nuclear genes. However, the underlying molecular mechanisms remain unresolved. In this study, we demonstrate that the Topo VI subunit BIN4 interacts with the cohesin subunit AtSMC3. We also show that, similarly to Topo VI mutants, a line suppressing AtSMC3 shows constitutive activation of singlet oxygen response genes and enhanced tolerance to photooxidative str...
bioRxiv (Cold Spring Harbor Laboratory), Apr 23, 2022
Communication between organelles and the nucleus is referred to as anterograde (nucleus to organe... more Communication between organelles and the nucleus is referred to as anterograde (nucleus to organelle) and retrograde (organelle to nucleus) signalling. In plants, the pentatricopeptide repeat (PPR) proteins represent a large family of nuclear-encoded proteins that are required for post-transcriptional control of chloroplast and mitochondria gene expression, and hence play a central role in the nuclear anterograde control of organelle genome expression. How PPR gene expression is controlled and regulated by retrograde signals is, however, still unknown. Here, we report a significant role for the general transcription factor TFIIF αsubunit (TFIIFα) in controlling PPR gene expression in Arabidopsis. First, we found that TFIIFα interacts with the BIN4 subunit of the Topoisomerase VI (Topo VI). Transcriptome analysis of TFIIF and Topo VI mutant lines then revealed that many PLS-type PPR genes involved in RNA editing are reciprocally controlled by TFIIF and Topo VI. The misexpression of CLB19 and DYW1 genes in two allelic tfIIfα mutants was associated with editing impairments in their plastid target RNAs rpoA and ndhD, respectively. Interestingly, we also detected a change in NDH activity in tfIIfα plants. We also show that TFIIF and Topo VI coordinate the expression of NDH subunits encoded by the nuclear and plastid genomes. These results reveal the crucial role of the nuclear TFIIFα and Topo VI complexes in controlling plastid genome expression at multiple levels of regulation, including the particular regulation of PPR gene expression.
Frontiers in Plant Science
As in other eukaryotes, the plant genome is functionally organized in two mutually exclusive chro... more As in other eukaryotes, the plant genome is functionally organized in two mutually exclusive chromatin fractions, a gene-rich and transcriptionally active euchromatin, and a gene-poor, repeat-rich, and transcriptionally silent heterochromatin. In Drosophila and humans, the molecular mechanisms by which euchromatin is preserved from heterochromatin spreading have been extensively studied, leading to the identification of insulator DNA elements and associated chromatin factors (insulator proteins), which form boundaries between chromatin domains with antagonistic features. In contrast, the identity of factors assuring such a barrier function remains largely elusive in plants. Nevertheless, several genomic elements and associated protein factors have recently been shown to regulate the spreading of chromatin marks across their natural boundaries in plants. In this minireview, we focus on recent findings that describe the spreading of chromatin and propose avenues to improve the underst...
TOULOUSE3-BU Sciences (315552104) / SudocSudocFranceF
Frontiers in Plant Science, 2020
Plants use solar radiation as energy source for photosynthesis. They also take advantage of the i... more Plants use solar radiation as energy source for photosynthesis. They also take advantage of the information provided by the varying properties of sunlight, such as wavelength, orientation, and periodicity, to trigger physiological and developmental adaptations to a changing environment. After more than a century of research efforts in plant photobiology, multiple light signaling pathways converging onto chromatin-based mechanisms have now been identified, which in some instances play critical roles in plant phenotypic plasticity. In addition to locus-specific changes linked to transcription regulation, light signals impact higher-order chromatin organization. Here, we summarize current knowledge on how light can affect the global composition and the spatial distribution of chromatin domains. We introduce emerging questions on the functional links between light signaling and the epigenome, and further discuss how different chromatin regulatory layers may interconnect during plant adaptive responses to light.
The organization of the genome into transcriptionally active and inactive chromatin domains requi... more The organization of the genome into transcriptionally active and inactive chromatin domains requires well-delineated chromatin boundaries and insulator functions in order to maintain the identity of adjacent genomic loci with antagonistic chromatin marks and functionality. In plants that lack known chromatin insulators, the mechanisms that prevent heterochromatin spreading into euchromatin remain to be identified. Here, we show that DNA Topoisomerase VI participates in a chromatin boundary function that safeguards the expression of genes in euchromatin islands within silenced heterochromatin regions. While some transposable elements are reactivated in mutants of the Topoisomerase VI complex, genes insulated in euchromatin islands within heterochromatic regions of theArabidopsis thalianagenome are specifically downregulated. H3K9me2 levels consistently increase at euchromatin island loci and decrease at some TE loci. We further show that Topoisomerase VI physically interacts with S-a...
Journal of Visualized Experiments, 2016
Photosynthesis Research, 2004
Thioredoxins, by reducing disulfide bridges are one of the main participants that regulate cellul... more Thioredoxins, by reducing disulfide bridges are one of the main participants that regulate cellular redox balance. In plants, the thioredoxin system is particularly complex. The most well-known thioredoxins are the chloroplastic ones, that participate in the regulation of enzymatic activities during the transition between light and dark phases. The mitochondrial system composed of NADPH-dependent thioredoxin reductase and type o thioredoxin has only recently been described. The type h thioredoxin group is better known. Yeast complementation experiments demonstrated that Arabidopsis thaliana thioredoxins h have divergent functions, at least in Saccharomyces cerevisiae. They have diverse affinities for different target proteins, most probably because of structural differences. However, plant thioredoxin h functions still have to be defined.
Cellular and Molecular Life Sciences, 2015
Exposure of plants to adverse environmental conditions leads to extensive transcriptional changes... more Exposure of plants to adverse environmental conditions leads to extensive transcriptional changes. Genome-wide approaches and gene function studies have revealed the importance of chromatin-level control in the regulation of stress-responsive gene expression. Advances in understanding chromatin modifications implicated in plant stress response and identifying proteins involved in chromatin-mediated transcriptional responses to stress are briefly presented in this review. We then highlight how chromatin-mediated gene expression changes can be coupled to the metabolic status of the cell, since many of the chromatin-modifying proteins involved in transcriptional regulation depend on cofactors and metabolites that are shared with enzymes in basic metabolism. Lastly, we discuss the stability and heritability of stress-induced chromatin changes and the potential of chromatin-based strategies for increasing stress tolerance of crops.
Frontiers in Plant Science, 2015
The Plant Journal, 2009
Shortly after the release of singlet oxygen ((1)O(2)) in chloroplasts, changes in nuclear gene ex... more Shortly after the release of singlet oxygen ((1)O(2)) in chloroplasts, changes in nuclear gene expression occur in the conditional flu mutant of Arabidopsis that reveal a rapid transfer of signals from the plastid to the nucleus. Extensive genetic screens aimed at identifying constituents involved in (1)O(2)-mediated plastid-to-nucleus signaling have failed to identify extraplastidic signaling components. This finding suggests that (1)O(2)-mediated signals are not translocated to the nucleus via a single linear pathway, but rather through a signaling network that is difficult to block by single mutations. The complexity of this signaling network has been tackled by mutagenizing a transgenic flu line expressing the luciferase reporter gene under the control of the promoter of a (1)O(2)-responsive AAA-ATPase gene (At3g28580) and isolating second site mutants that constitutively express the reporter gene at a high level. One of the mutants was shown by map-based cloning and sequencing to contain a single amino acid change in the PLEIOTROPIC RESPONSE LOCUS 1 (PRL1) protein. PRL1 suppresses the expression of AAA-ATPase and other (1)O(2)-responsive genes. PRL1 seems to play a major role in modulating responses of plants to environmental changes by interconnecting (1)O(2)-mediated retrograde signaling with other signaling pathways.
The Plant Journal, 2009
The conditional flu mutant of Arabidopsis thaliana generates singlet oxygen (1 O 2) in plastids d... more The conditional flu mutant of Arabidopsis thaliana generates singlet oxygen (1 O 2) in plastids during a darkto-light shift. Seedlings of flu bleach and die, whereas mature plants stop growing and develop macroscopic necrotic lesions. Several suppressor mutants, dubbed singlet oxygen-linked death activator (soldat), were identified that abrogate 1 O 2-mediated cell death of flu seedlings. One of the soldat mutations, soldat10, affects a gene encoding a plastid-localized protein related to the human mitochondrial transcription termination factor mTERF. As a consequence of this mutation, plastid-specific rRNA levels decrease and protein synthesis in plastids of soldat10 is attenuated. This disruption of chloroplast homeostasis in soldat10 seedlings affects communication between chloroplasts and the nucleus and leads to changes in the steady-state concentration of nuclear gene transcripts. The soldat10 seedlings suffer from mild photo-oxidative stress, as indicated by the constitutive up-regulation of stress-related genes. Even though soldat10/flu seedlings overaccumulate the photosensitizer protochlorophyllide in the dark and activate the expression of 1 O 2-responsive genes after a dark-to-light shift they do not show a 1 O 2-dependent cell death response. Disturbance of chloroplast homeostasis in emerging soldat10/flu seedlings seems to antagonize a subsequent 1 O 2-mediated cell death response without suppressing 1 O 2-dependent retrograde signaling. The results of this work reveal the unexpected complexity of what is commonly referred to as 'plastid signaling'.
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Papers by Christophe Laloi