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10 publication(s) since Avril 2010:

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10/2018 | plant j   IF 5.8
The multistress-induced Translocator protein (TSPO) differentially modulates storage lipids metabolism in seeds and seedlings.
Jurkiewicz P, Melser S, Maucourt M, Ayeb H, Veljanovski V, Maneta-Peyret L, Hooks M, Rolin D, Moreau P, Batoko H

Translocator proteins (TSPO) are conserved membrane proteins extensively studied in mammals, but their function is still unclear. Angiosperm TSPO are transiently induced by abiotic stresses in vegetative tissues. We showed previously that constitutive expression of the Arabidopsis TSPO (AtTSPO) could be detrimental to the cell. Degradation of AtTSPO requires an active autophagy pathway. We show here that genetic modifications of TSPO expression in plant and yeast cells reduce the levels of cytoplasmic lipid droplets (LD). Transgenic Arabidopsis seedlings overexpressing AtTSPO contain less LD as compared with wild type (WT). LD levels were increased in Arabidopsis AtTSPO knockout (KO) seedlings. Deletion of the Schizosaccharomyces pombe TSPO resulted in an increase in LD level in the cell. As compared with the WT, the mutant strain was more sensitive to cerulenin, an inhibitor of fatty acids and sterol biosynthesis. We found that in contrast with seedlings, overexpression of AtTSPO (OE) resulted in an up to 50% increase in seeds fatty acids as compared with WT. A time course experiment revealed that after 4 days of seed imbibition, the levels of triacylglycerol (TAG) was still higher in the OE seeds as compared with WT or KO seeds. However, the de novo synthesis of phospholipids and TAG after 24 h of imbibition was substantially reduced in OE seeds as compared with WT or KO seeds. Our findings support a plant TSPO role in energy homeostasis in a tissue-specific manner, enhancing fatty acids and LD accumulation in mature seeds and limiting LD levels in seedlings.

07/09/2018 | Sci Rep   IF 4.1
The Arabidopsis RNA Polymerase II Carboxyl Terminal Domain (CTD) Phosphatase-Like1 (CPL1) is a biotic stress susceptibility gene.
Thatcher LF, Foley R, Casarotto HJ, Gao LL, Kamphuis LG, Melser S, Singh KB

Crop breeding for improved disease resistance may be achieved through the manipulation of host susceptibility genes. Previously we identified multiple Arabidopsis mutants known as enhanced stress response1 (esr1) that have defects in a KH-domain RNA-binding protein and conferred increased resistance to the root fungal pathogen Fusarium oxysporum. Here, screening the same mutagenized population we discovered two further enhanced stress response mutants that also conferred enhanced resistance to F. oxysporum. These mutants also have enhanced resistance to a leaf fungal pathogen (Alternaria brassicicola) and an aphid pest (Myzus persicae), but not to the bacterial leaf pathogen Pseudomonas syringae. The causal alleles in these mutants were found to have defects in the ESR1 interacting protein partner RNA Polymerase II Carboxyl Terminal Domain (CTD) Phosphatase-Like1 (CPL1) and subsequently given the allele symbols cpl1-7 and cpl1-8. These results define a new role for CPL1 as a pathogen and pest susceptibility gene. Global transcriptome analysis and oxidative stress assays showed these cpl1 mutants have increased tolerance to oxidative stress. In particular, components of biotic stress responsive pathways were enriched in cpl1 over wild-type up-regulated gene expression datasets including genes related to defence, heat shock proteins and oxidative stress/redox state processes.

05/06/2018 | Cell Rep   IF 8
Ubiquitin-Dependent Degradation of Mitochondrial Proteins Regulates Energy Metabolism.
Lavie J, De Belvalet H, Sonon S, Ion AM, Dumon E, Melser S, Lacombe D, Dupuy JW, Lalou C, Benard G

The ubiquitin proteasome system (UPS) regulates many cellular functions by degrading key proteins. Notably, the role of UPS in regulating mitochondrial metabolic functions is unclear. Here, we show that ubiquitination occurs in different mitochondrial compartments, including the inner mitochondrial membrane, and that turnover of several metabolic proteins is UPS dependent. We specifically detailed mitochondrial ubiquitination and subsequent UPS-dependent degradation of succinate dehydrogenase subunit A (SDHA), which occurred when SDHA was minimally involved in mitochondrial energy metabolism. We demonstrate that SDHA ubiquitination occurs inside the organelle. In addition, we show that the specific inhibition of SDHA degradation by UPS promotes SDHA-dependent oxygen consumption and increases ATP, malate, and citrate levels. These findings suggest that the mitochondrial metabolic machinery is also regulated by the UPS.

2015 | Biochim Biophys Acta   IF 3.7
Mitochondrial degradation and energy metabolism
Melser S, Lavie J, Benard G

Mitochondria are intracellular power plants that feed most eukaryotic cells with the ATP produced by the oxidative phosphorylation (OXPHOS). Mitochondrial energy production is controlled by many regulatory mechanisms. The control of mitochondrial mass through both mitochondrial biogenesis and degradation has been proposed to be one of the most important regulatory mechanisms. Recently, autophagic degradation of mitochondria has emerged as an important mechanism involved in the regulation of mitochondrial quantity and quality. In this review, we highlight the intricate connections between mitochondrial energy metabolism and mitochondrial autophagic degradation by showing the importance of mitochondrial bioenergetics in this process and illustrating the role of mitophagy in mitochondrial patho-physiology. Furthermore, we discuss how energy metabolism could coordinate the biogenesis and degradation of this organelle.

2015 | bmc plant biol   IF 3.9
Analysis of conglutin seed storage proteins across lupin species using transcriptomic, protein and comparative genomic approaches.
Foley RC, Jimenez-Lopez JC, Kamphuis LG, Hane JK, Melser S, Singh KB

BACKGROUND: The major proteins in lupin seeds are conglutins that have primary roles in supplying carbon, sulphur and nitrogen and energy for the germinating seedling. They fall into four families; alpha, beta, gamma and delta. Interest in these conglutins is growing as family members have been shown to have beneficial nutritional and pharmaceutical properties. RESULTS: An in-depth transcriptome and draft genome from the narrow-leafed lupin (NLL; Lupinus angustifolius) variety, Tanjil, were examined and 16 conglutin genes were identified. Using RNAseq data sets, the structure and expression of these 16 conglutin genes were analysed across eight lupin varieties from five lupin species. Phylogenic analysis suggest that the alpha and gamma conglutins diverged prior to lupin speciation while beta and delta members diverged both prior and after speciation. A comparison of the expression of the 16 conglutin genes was performed, and in general the conglutin genes showed similar levels of RNA expression among varieties within species, but quite distinct expression patterns between lupin species. Antibodies were generated against the specific conglutin families and immunoblot analyses were used to compare the levels of conglutin proteins in various tissues and during different stages of seed development in NLL, Tanjil, confirming the expression in the seed. This analysis showed that the conglutins were expressed highly at the mature seed stage, in all lupin species, and a range of polypeptide sizes were observed for each conglutin family. CONCLUSIONS: This study has provided substantial information on the complexity of the four conglutin families in a range of lupin species in terms of their gene structure, phylogenetic relationships as well as their relative RNA and protein abundance during seed development. The results demonstrate that the majority of the heterogeneity of conglutin polypeptides is likely to arise from post-translational modification from a limited number of precursor polypeptides rather than a large number of different genes. Overall, the results demonstrate a high degree of plasticity for conglutin expression during seed development in different lupin species.

07/05/2013 | Cell Metab   IF 20.6
Rheb Regulates Mitophagy Induced by Mitochondrial Energetic Status
Melser S, Hebert-Chatelain E, Lavie J, et al., Benard G

Mitophagy has been recently described as a mechanism of elimination of damaged organelles. Although the regulation of the amount of mitochondria is a core issue concerning cellular energy homeostasis, the relationship between mitochondrial degradation and energetic activity has not yet been considered. Here, we report that the stimulation of mitochondrial oxidative phosphorylation enhances mitochondrial renewal by increasing its degradation rate. Upon high oxidative phosphorylation activity, we found that the small GTPase Rheb is recruited to the mitochondrial outer membrane. This mitochondrial localization of Rheb promotes mitophagy through a physical interaction with the mitochondrial autophagic receptor Nix and the autophagosomal protein LC3-II. Thus, Rheb-dependent mitophagy contributes to the maintenance of optimal mitochondrial energy production. Our data suggest that mitochondrial degradation contributes to a bulk renewal of the organelle in order to prevent mitochondrial aging and to maintain the efficiency of oxidative phosphorylation.

03/2013 | Antioxid Redox Signal   IF 6.5
Mitoplasticity: adaptation biology of the mitochondrion to the cellular redox state in physiology and carcinogenesis
Jose C, Melser S, Benard G, Rossignol R

Adaptation and transformation biology of the mitochondrion to redox status is an emerging domain of physiology and pathophysiology. Mitochondrial adaptations occur in response to accidental changes in cellular energy demand or supply while mitochondrial transformations are a part of greater program of cell metamorphosis. The possible role of mitochondrial adaptations and transformations in pathogenesis remains unexplored, and it has become critical to decipher the stimuli and the underlying molecular pathways. Immediate activation of mitochondrial function was described during acute exercise, respiratory chain injury, Endoplasmic Reticulum stress, genotoxic stress, or environmental toxic insults. Delayed adaptations of mitochondrial form, composition, and functions were evidenced for persistent changes in redox status as observed in endurance training, in fibroblasts grown in presence of respiratory chain inhibitors or in absence of glucose, in the smooth muscle of patients with severe asthma, or in the skeletal muscle of patients with a mitochondrial disease. Besides, mitochondrial transformations were observed in the course of human cell differentiation, during immune response activation, or in cells undergoing carcinogenesis. Little is known on the signals and downstream pathways that govern mitochondrial adaptations and transformations. Few adaptative loops, including redox sensors, kinases, and transcription factors were deciphered, but their implication in physiology and pathology remains elusive. Mitoplasticity could play a protective role against aging, diabetes, cancer, or neurodegenerative diseases. Research on adaptation and transformation could allow the design of innovative therapies, notably in cancer

07/2012 | anal bioanal chem   IF 3.3
Rapid nanoscale quantitative analysis of plant sphingolipid long-chain bases by GC-MS.
Cacas JL, Melser S, Domergue F, Joubes J, Bourdenx B, Schmitter JM, Mongrand S

In eukaryotic organisms, sphingolipids are major structural lipids of biological membranes and perform additional essential functions as signalling molecules. While long-chain bases (LCB), the common precursor to all sphingolipid classes, is represented by only one major molecular species in animals and fungi, up to nine LCB have been found in plants. In the absence of genuine plant sphingolipid references required for proper quantification, we have reinvestigated and optimized a protocol destined to the quantification of total plant LCB that relies on the use of gas chromatography-mass spectrometry (GC-MS). This rapid three-step protocol sequentially involves (1) the release of LCB from biological samples using barium hydroxide solution, (2) their oxidation into aldehydes by metaperiodate, and (3) the subsequent identification/quantification of these aldehydes by GC-MS. It is simple and reliable and enables separation of aldehydes upon their stero-specificity. It further enables the quantification of total LCB from a wide variety of samples including yeast and animal cell cultures.

02/2011 | plant cell rep   IF 3
Links between lipid homeostasis, organelle morphodynamics and protein trafficking in eukaryotic and plant secretory pathways.
Melser S, Molino D, Batailler B, Peypelut M, Laloi M, Wattelet-Boyer V, Bellec Y, Faure JD, Moreau P

The role of lipids as molecular actors of protein transport and organelle morphology in plant cells has progressed over the last years through pharmacological and genetic investigations. The manuscript is reviewing the roles of various lipid families in membrane dynamics and trafficking in eukaryotic cells, and summarizes some of the related physicochemical properties of the lipids involved. The article also focuses on the specific requirements of the sphingolipid glucosylceramide (GlcCer) in Golgi morphology and protein transport through the plant secretory pathway. The use of a specific inhibitor of plant glucosylceramide synthase and selected Arabidopsis thaliana RNAi lines stably expressing several markers of the plant secretory pathway, establishes specific steps sensitive to GlcCer biosynthesis. Collectively, data of the literature demonstrate the existence of links between protein trafficking, organelle morphology, and lipid metabolism/homeostasis in eukaryotic cells including plant cells.

04/2010 | traffic   IF 4.4
Glucosylceramide biosynthesis is involved in Golgi morphology and protein secretion in plant cells.
Melser S, Batailler B, Peypelut M, Poujol C, Bellec Y, Wattelet-Boyer V, Maneta-Peyret L, Faure JD, Moreau P

Lipids have an established role as structural components of membranes or as signalling molecules, but their role as molecular actors in protein secretion is less clear. The complex sphingolipid glucosylceramide (GlcCer) is enriched in the plasma membrane and lipid microdomains of plant cells, but compared to animal and yeast cells, little is known about the role of GlcCer in plant physiology. We have investigated the influence of GlcCer biosynthesis by glucosylceramide synthase (GCS) on the efficiency of protein transport through the plant secretory pathway and on the maintenance of normal Golgi structure. We determined that GlcCer is synthesized at the beginning of the plant secretory pathway [mainly endoplasmic reticulum (ER)] and that D,L-threo-1-phenyl-2-decanoyl amino-3-morpholino-propanol (PDMP) is a potent inhibitor of plant GCS activity in vitro and in vivo. By an in vivo confocal microscopy approach in tobacco leaves infiltrated with PDMP, we showed that the decrease in GlcCer biosynthesis disturbed the transport of soluble and membrane secretory proteins to the cell surface, as these proteins were partly retained intracellularly in the ER and/or Golgi. Electron microscopic observations of Arabidopsis thaliana root cells after high-pressure freezing and freeze substitution evidenced strong morphological changes in the Golgi bodies, pointing to a link between decreased protein secretion and perturbations of Golgi structure following inhibition of GlcCer biosynthesis in plant cells.