Implication des protéines tyrosine phosphatases dans la signalisation de l' acide abscissique chez Arabidopsis thaliana

PARIS-BIUSJ-Thèses (751052125) / SudocPARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceF

Characterization of three hormone mutants of Nicotiana plumbaginifolia: evidence for a common ABA deficiency

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The response to auxin of rapeseed (Brassica napus L.) roots displaying reduced gravitropism due to transformation by Agrobacterium rhizogenes

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HPLC-Elisa and MS as complementary techniques to study plant hormone metabolites

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Induction of Abscisic Acid-Regulated Gene Expression by Diacylglycerol Pyrophosphate Involves Ca(2+) and Anion Currents in Arabidopsis Suspension Cells

Diacylglycerol pyrophosphate (DGPP) was recently shown to be a possible intermediate in abscisic acid (ABA) signaling. In this study, reverse transcription-PCR of ABA up-regulated genes was used to evaluate the ability of DGPP to trigger gene expression in Arabidopsis (Arabidopsis thaliana) suspension cells. At5g06760, LTI30, RD29A, and RAB18 were stimulated by ABA and also specifically expressed in DGPP-treated cells. Use of the Ca(2+) channel blockers fluspirilene and pimozide and the Ca(2+) chelator EGTA showed that Ca(2+) was required for ABA induction of DGPP formation. In addition, Ca(2+) participated in DGPP induction of gene expression via stimulation of anion currents. Hence, a sequence of Ca(2+), DGPP, and anion currents, constituting a core of early ABA-signaling events necessary for gene expression, is proposed

The mitogen-activated protein kinase phosphatase PHS1 regulates flowering in Arabidopsis thaliana

International audienceArabidopsis PHS1, initially known as an actor of cytoskeleton organization, is a positive regulator of flowering in the photoperiodic and autonomous pathways by modulating both CO and FLC mRNA levels. Protein phosphorylation and dephosphorylation is a major type of post-translational modification, controlling many biological processes. In Arabidopsis thaliana, five genes encoding MAPK phosphatases (MKP)-like proteins have been identified. Among them, PROPYZAMIDE HYPERSENSITIVE 1 (PHS1) encoding a dual-specificity protein tyrosine phosphatase (DsPTP) has been shown to be involved in microtubule organization, germination and ABA-regulated stomatal opening. Here, we demonstrate that PHS1 also regulates flowering under long-day and short-day conditions. Using physiological, genetic and molecular approaches, we have shown that the late flowering phenotype of the knock-out phs1-5 mutant is linked to a higher expression of FLOWERING LOCUS C (FLC). In contrast, a decline of both CONSTANS (CO) and FLOWERING LOCUS T (FT) expression is observed in the knock-out phs1-5 mutant, especially at the end of the light period under long-day conditions when the induction of flowering occurs. We show that this partial loss of sensitivity to photoperiodic induction is independent of FLC. Our results thus indicate that PHS1 plays a dual role in flowering, in the photoperiodic and autonomous pathways, by modulating both CO and FLC mRNA levels. Our work reveals a novel actor in the complex network of the flowering regulation

Tl-DNA transformation decreases ABA level

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Auxin metabolism and rooting in young and mature clones of Sequoia sempervirens

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Proline oxidation fuels mitochondrial respiration during dark-induced leaf senescence in Arabidopsis thaliana

International audienceLeaf senescence is a form of developmentally programmed cell death that allows the remobilization of nutrients and cellular materials from leaves to sink tissues and organs. Among the catabolic reactions that occur upon senescence, little is known about the role of proline catabolism. In this study, the involvement in dark-induced senescence of pro-line dehydrogenases (ProDHs), which catalyse the first and rate-limiting step of proline oxidation in mitochondria, was investigated using prodh single-and double-mutants with the help of biochemical, proteomic, and metabolomic approaches. The presence of ProDH2 in mitochondria was confirmed by mass spectrometry and immunogold labelling in dark-induced leaves of Arabidopsis. The prodh1 prodh2 mutant exhibited enhanced levels of most tricarb-oxylic acid cycle intermediates and free amino acids, demonstrating a role of ProDH in mitochondrial metabolism. We also found evidence of the involvement and the importance of ProDH in respiration, with proline as an alternative substrate, and in remobilization of proline during senescence to generate glutamate and energy that can then be exported to sink tissues and organs

Acyl Chains of Phospholipase D Transphosphatidylation Products in Arabidopsis Cells: A Study Using Multiple Reaction Monitoring Mass Spectrometry

<div><h3>Background</h3><p>Phospholipases D (PLD) are major components of signalling pathways in plant responses to some stresses and hormones. The product of PLD activity is phosphatidic acid (PA). PAs with different acyl chains do not have the same protein targets, so to understand the signalling role of PLD it is essential to analyze the composition of its PA products in the presence and absence of an elicitor.</p> <h3>Methodology/Principal findings</h3><p>Potential PLD substrates and products were studied in <em>Arabidopsis thaliana</em> suspension cells treated with or without the hormone salicylic acid (SA). As PA can be produced by enzymes other than PLD, we analyzed phosphatidylbutanol (PBut), which is specifically produced by PLD in the presence of <em>n</em>-butanol. The acyl chain compositions of PBut and the major glycerophospholipids were determined by multiple reaction monitoring (MRM) mass spectrometry. PBut profiles of untreated cells or cells treated with SA show an over-representation of 160/18∶2- and 16∶0/18∶3-species compared to those of phosphatidylcholine and phosphatidylethanolamine either from bulk lipid extracts or from purified membrane fractions. When microsomal PLDs were used in <em>in vitro</em> assays, the resulting PBut profile matched exactly that of the substrate provided. Therefore there is a mismatch between the acyl chain compositions of putative substrates and the <em>in vivo</em> products of PLDs that is unlikely to reflect any selectivity of PLDs for the acyl chains of substrates.</p> <h3>Conclusions</h3><p>MRM mass spectrometry is a reliable technique to analyze PLD products. Our results suggest that PLD action in response to SA is not due to the production of a stress-specific molecular species, but that the level of PLD products <em>per se</em> is important. The over-representation of 160/18∶2- and 16∶0/18∶3-species in PLD products when compared to putative substrates might be related to a regulatory role of the heterogeneous distribution of glycerophospholipids in membrane sub-domains.</p> </div