New clues for a cold case: nitric oxide response to low temperature

International audienceLow temperature is among the most frequent stresses met by plants during their lifespan, and a plant's ability to cold-acclimate is a determinant for further growth and development. Although intensive research has provided a good picture of the molecular and metabolic changes triggered by cold, the underlying regulatory mechanisms remain elusive and are thus being actively sought. Recent studies have shed light on the importance of nitric oxide (NO), a ubiquitous signalling molecule in eukaryotes, for plant tolerance to chilling and freezing. Indeed, NO formation following cold exposure has been reported in a range of plant species, and a series of proteins targeted by NO-based post-translational modifications have been identified. Moreover, key cold-regulated genes have been characterized as NO-dependent, suggesting the crucial importance of NO signalling for cold-responsive gene expression. This review provides a picture of our current understanding of the function of NO in the context of plant response to cold. Particular attention is dedicated to the open questions left by the fragmented data currently available concerning NO formation, transduction and biological significance for plant adaptation to low temperature. Although nitric oxide (NO) is now recognized as a versatile actor of stress signalling networks in plants, its involvement in cold stress responses emerged very recently. During the past few years, the identification of proteins and genes targeted by NO signalling, together with the key functions of these targets for cold tolerance, supported the importance of NO for establishing tolerance to low temperature. This review summarizes our current knowledge on this topic by addressing different aspects of NO signalling (generation and removal, impact on protein function and gene expression, overall impact on cold response) and proposing directions for future investigations

Etude de l'expression des gènes de l'acyl-CoA élongase au cours du développement de la graine de colza (Brassica napus)

Le but de cette étude était de comprendre la régulation de la synthèse des acides gras à très longues chaînes, et, plus particulièrement, de l'acide érucique, pendant le développement de la graine de colza. L'acyl-CoA élongase qui synthétise l'acide érucique est un complexe enzymatique constitué de quatre enzymes catalysant des réactions successives. Seuls les gènes codant la 3-cétoacyl-CoA synthase, la première enzyme du complexe, étaient connus. Deux ADNc complets, BN-KCR 1 et BN-KCR 2, codant putativement pour la 3-cétoacyl-CoA réductase ont donc été clonés par le criblage d'une banque d'ADNc d'embryons de graine de colza. Nous avons montré, lors du développement de la graine, que l'expression de la 3-cétoacyl-CoA synthase étai régulée au niveau post-transcriptionnel alors que celle de la 3-cétoacyl-CoA réductase l'était principalement au niveau transcriptionnel. De plus, les ARNm BN-KCR sont exprimés dans tous les tissus avec une expression majoritaire dans les graines.BORDEAUX2-BU Santé (330632101) / SudocSudocFranceF

Physiological and Environmental Regulation of Seed Germination: From Signaling Events to Molecular Responses

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Dual Targeting of Arabidopsis HOLOCARBOXYLASE SYNTHETASE1: A Small Upstream Open Reading Frame Regulates Translation Initiation and Protein Targeting.

Protein biotinylation is an original and very specific posttranslational modification, compartmented in plants, between mitochondria, plastids, and the cytosol. This reaction modifies and activates few carboxylases committed in key metabolisms and is catalyzed by holocarboxylase synthetase (HCS). The molecular bases of this complex compartmentalization and the relative function of each of the HCS genes, HCS1 and HCS2, identified in Arabidopsis (Arabidopsis thaliana) are mainly unknown. Here, we showed by reverse genetics that the HCS1 gene is essential for plant viability, whereas disruption of the HCS2 gene in Arabidopsis does not lead to any obvious phenotype when plants are grown under standard conditions. These findings strongly suggest that HCS1 is the only protein responsible for HCS activity in Arabidopsis cells, including the cytosolic, mitochondrial, and plastidial compartments. A closer study of HCS1 gene expression enabled us to propose an original mechanism to account for this multiplicity of localizations. Located in the HCS1 messenger RNA 5'-untranslated region, an upstream open reading frame regulates the translation initiation of HCS1 and the subsequent targeting of HCS1 protein. Moreover, an exquisitely precise alternative splicing of HCS1 messenger RNA can regulate the presence and absence of this upstream open reading frame. The existence of these complex and interdependent mechanisms creates a rich molecular platform where different parameters and factors could control HCS targeting and hence biotin metabolism

Tyrosine and Phenylalanine Are Synthesized within the Plastids in Arabidopsis1[W]

While the presence of a complete shikimate pathway within plant plastids is definitively established, the existence of a cytosolic postchorismate portion of the pathway is still debated. This question is alimented by the presence of a chorismate mutase (CM) within the cytosol. Until now, the only known destiny of prephenate, the product of CM, is incorporation into tyrosine (Tyr) and/or phenylalanine (Phe). Therefore, the presence of a cytosolic CM suggests that enzymes involved downstream of CM in Tyr or Phe biosynthesis could be present within the cytosol of plant cells. It was thus of particular interest to clarify the subcellular localization of arogenate dehydrogenases (TYRAs) and arogenate dehydratases (ADTs), which catalyze the ultimate steps in Tyr and Phe biosynthesis, respectively. The aim of this study was to address this question in Arabidopsis (Arabidopsis thaliana) by analysis of the subcellular localization of the two TYRAAts and the six AtADTs. This article excludes the occurrence of a spliced TYRAAt1 transcript encoding a cytosolic TYRA protein. Transient expression analyses of TYRA- and ADT-green fluorescent protein fusions reveal that the two Arabidopsis TYRA proteins and the six ADT proteins are all targeted within the plastid. Accordingly, TYRA and ADT proteins were both immunodetected in the chloroplast soluble protein fraction (stroma) of Arabidopsis. No TYRA or ADT proteins were immunodetected in the cytosol of Arabidopsis cells. Taken together, all our data exclude the possibility of Tyr and/or Phe synthesis within the cytosol, at least in green leaves and Arabidopsis cultured cells

Dynamics of Protein Phosphorylation during Arabidopsis Seed Germination

Seed germination is critical for early plantlet development and is tightly controlled by environmental factors. Nevertheless, the signaling networks underlying germination control remain elusive. In this study, the remodeling of Arabidopsis seed phosphoproteome during imbibition was investigated using stable isotope dimethyl labeling and nanoLC-MS/MS analysis. Freshly harvested seeds were imbibed under dark or constant light to restrict or promote germination, respectively. For each light regime, phosphoproteins were extracted and identified from dry and imbibed (6 h, 16 h, and 24 h) seeds. A large repertoire of 10,244 phosphopeptides from 2546 phosphoproteins, including 110 protein kinases and key regulators of seed germination such as Delay Of Germination 1 (DOG1), was established. Most phosphoproteins were only identified in dry seeds. Early imbibition led to a similar massive downregulation in dormant and non-dormant seeds. After 24 h, 411 phosphoproteins were specifically identified in non-dormant seeds. Gene ontology analyses revealed their involvement in RNA and protein metabolism, transport, and signaling. In addition, 489 phosphopeptides were quantified, and 234 exhibited up or downregulation during imbibition. Interaction networks and motif analyses revealed their association with potential signaling modules involved in germination control. Our study provides evidence of a major role of phosphosignaling in the regulation of Arabidopsis seed germination

Synergistic toxicity between glyphosate and 2,4-dinitrophenol on budding yeast is not due to H₂O₂-mediated oxidative stress

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Constitutive salicylic acid accumulation in pi4kIII beta 1 beta 2 Arabidopsis plants stunts rosette but not root growth

International audiencePhospholipids have recently been found to be integral elements of hormone signalling pathways. An Arabidopsis thaliana double mutant in two type III phosphatidylinositol-4-kinases (PI4Ks), pi4kIII beta 1 beta 2, displays a stunted rosette growth. The causal link between PI4K activity and growth is unknown. Using microarray analysis, quantitative reverse transcription polymerase chain reaction (RT-qPCR) and multiple phytohormone analysis by LC-MS we investigated the mechanism responsible for the pi4kIII beta 1 beta 2 phenotype. The pi4kIII beta 1 beta 2 mutant accumulated a high concentration of salicylic acid (SA), constitutively expressed SA marker genes including PR-1, and was more resistant to Pseudomonas syringae. pi4kIII beta 1 beta 2 was crossed with SA signalling mutants eds1 and npr1 and SA biosynthesis mutant sid2 and NahG. The dwarf phenotype of pi4kIII beta 1 beta 2 rosettes was suppressed in all four triple mutants. Whereas eds1 pi4kIII beta 1 beta 2, sid2 pi4kIII beta 1 beta 2 and NahG pi4kIII beta 1 beta 2 had similar amounts of SA as the wild-type (WT), npr1pi4kIII beta 1 beta 2 had more SA than pi4kIII beta 1 beta 2 despite being less dwarfed. This indicates that PI4KIII beta 1 and PI4KIII beta 2 are genetically upstream of EDS1 and need functional SA biosynthesis and perception through NPR1 to express the dwarf phenotype. The slow root growth phenotype of pi4kIII beta 1 beta 2 was not suppressed in any of the triple mutants. The pi4kIII beta 1 beta 2 mutations together cause constitutive activation of SA signalling that is responsible for the dwarf rosette phenotype but not for the short root phenotype

The Arabidopsis DREB2 genetic pathway is constitutively repressed by basal phosphoinositide-dependent phospholipase C coupled to diacylglycerol kinase

International audiencePhosphoinositide-dependent phospholipases C (PI-PLCs) are activated in response to various stimuli. They utilize substrates provided by type III-Phosphatidylinositol-4 kinases (PI4KIII) to produce inositol triphosphate and diacylglycerol (DAG) that is phosphorylated into phosphatidic acid (PA) by DAG-kinases (DGKs). The roles of PI4KIIIs, PI-PLCs, and DGKs in basal signaling are poorly understood. We investigated the control of gene expression by basal PI-PLC pathway in Arabidopsis thaliana suspension cells. A transcriptome-wide analysis allowed the identification of genes whose expression was altered by edelfosine, 30 μM wortmannin, or R59022, inhibitors of PI-PLCs, PI4KIIIs, and DGKs, respectively. We found that a gene responsive to one of these molecules is more likely to be similarly regulated by the other two inhibitors. The common action of these agents is to inhibit PA formation, showing that basal PI-PLCs act, in part, on gene expression through their coupling to DGKs. Amongst the genes up-regulated in presence of the inhibitors, were some DREB2 genes, in suspension cells and in seedlings. The DREB2 genes encode transcription factors with major roles in responses to environmental stresses, including dehydration. They bind to C-repeat motifs, known as Drought-Responsive Elements that are indeed enriched in the promoters of genes up-regulated by PI-PLC pathway inhibitors. PA can also be produced by phospholipases D (PLDs). We show that the DREB2 genes that are up-regulated by PI-PLC inhibitors are positively or negatively regulated, or indifferent, to PLD basal activity. Our data show that the DREB2 genetic pathway is constitutively repressed in resting conditions and that DGK coupled to PI-PLC is active in this process, in suspension cells and seedlings. We discuss how this basal negative regulation of DREB2 genes is compatible with their stress-triggered positive regulation