1,720,962 research outputs found
Stress-inducible and constitutive phosphoinositide pools have distinctive fatty acid patterns in Arabidopsis thaliana
No full textFunction and development of eukaryotic cells require tight control of diverse physiological processes. Numerous cellular processes are regulated by polyphosphoinositides, which interact with protein partners or mediate release of the second messenger, inositol 1,4,5-trisphosphate (InsP3). Emerging evidence suggests that different regulatory or signaling functions of polyphosphoinositides may be orchestrated by the establishment of distinct subcellular pools; the principles underlying pool-formation are, however, not understood. Arabidopsis plants exhibit transient increases in polyphosphoinositides with hyperosmotic stress, providing a model for comparing constitutive and stress-inducible polyphosphoinositide pools. Using a combination of thin-layer-chromatography and gaschromatography, phospholipids from stressed and nonstressed Arabidopsis plants were analyzed for their associated fatty acids. Under nonstress conditions structural phospholipids and phosphatidylinositol contained 50-70 mol% polyunsaturated fatty acids (PUFA), whereas polyphosphoinositides were more saturated (10-20 mol% PUFA). With hyperosmotic stress polyphosphoinositides with up to 70 mol% PUFA were formed that differed from constitutive species and coincided with a transient loss in unsaturated phosphatidylinositol. The patterns indicate inducible turnover of an unsaturated phosphatidylinositol pool, which accumulates under standard conditions and is primed for phosphorylation on stimulation. Metabolic analysis of wild-type and transgenic plants disturbed in phosphoinositide metabolism suggests that, in contrast to saturated species, unsaturated polyphosphoinositides are channeled toward InsP3-production
Oxylipin Signaling and Plant Growth
No full textOxylipins are derived from the oxidation of polyunsaturated fatty acids. Further conversion of the resulting fatty acid hydroperoxides gives rise to a multitude of oxylipin classes, including hydroxy-, oxo-, or keto fatty acids, volatile aldehydes, and the phytohormone, jasmonic acid (JA). Oxylipins may be structurally further diversified by esterification, i.e., to plastidial glycolipids, Arabidopsides, or conjugation to amino acids. Oxylipin research so far has focused mainly on the investigation of jasmonates and their roles in wound signaling and plant development. In contrast, the physiological roles of other oxylipins are by far less well understood, in part because enzymes responsible for their formation are not well characterized. This chapter aims at giving an overview of plant oxylipin signaling, highlighting recent discoveries of new roles for different oxylipins in the regulation of developmental or adaptational processes
Determination of content and fatty acid composition of unlabeled phosphoinositide species by thin-layer chromatography and gas chromatography
No full textRecent advances in research on the physiological roles of phosphoinositides in eukaryotic organisms indicate a need to distinguish molecular phosphoinositide species on the basis of their characteristic head groups as well as their glycerolipid moieties. Accurate identification of phosphoinositide species in biological samples poses an analytical challenge, because structurally similar inositol phosphate head groups must be resolved, as must lipid-associated fatty acids. Although intact phosphoinositide species have been successfully analyzed, such analyses employ state-of-the-art liquid chromatography/mass spectrometry and require expensive equipment not accessible to many researchers. Described here is a cost-efficient and reliable alternative developed by adaptation of a combination of classic methods for lipid analysis, thin-layer chromatography and gas chromatography. (C) 2008 Elsevier Inc. All rights reserved
Jasmonic acid perception by COI1 involves inositol polyphosphates in Arabidopsis thaliana
No full textPlant responses to wounding are part of their defense responses against insects, and are tightly regulated. The isoleucin conjugate of jasmonic acid (JA-IIe) is a major regulatory molecule. We have previously shown that inositol polyphosphate signals are required for defense responses in Arabidopsis; however, the way in which inositol polyphosphates contribute to plant responses to wounding has so far remained unclear. Arabidopsis F-box proteins involved in the perception of JA-IIe (COI1) and auxin (TIR1) are structurally similar. Because TIR1 has recently been shown to contain inositol hexakisphosphate (InsP(6)) as a co-factor of unknown function, here we explored the possibility that InsP(6) or another inositol polyphosphate is required for COI1 function. In support of this hypothesis, COI1 variants with changes in putative inositol polyphosphate coordinating residues exhibited a reduced interaction with the COI1 target, JAZ9, in yeast two-hybrid tests. The equivalent COI1 variants displayed a reduced capability to rescue jasmonate-mediated root growth inhibition or silique development in Arabidopsis col1 mutants. Yeast two-hybrid tests using wild-type COI1 in an ipk1 Delta yeast strain exhibiting increased levels of inositol pentakisphosphate (InsP(5)) and reduced levels of InsP(6) indicate an enhanced COI1/JAZ9 interaction. Consistent with these findings, Arabidopsis ipk1-1 mutants, also with increased InsP(5) and reduced InsP(6) levels, showed increased defensive capabilities via COI1-mediated processes, including wound-induced gene expression, defense against caterpillars or root growth inhibition by jasmonate. The combined data from experiments using mutated COI1 variants, as well as yeast and Arabidopsis backgrounds altered in inositol polyphosphate metabolism, indicate that an inositol polyphosphate, and probably InsP(5), contributes to COI1 function
Phosphoinositide and inositolpolyphosphate signalling in defense responses of Arabidopsis thaliana challenged by mechanical wounding
No full textVarious biochemical signals are implicated in Arabidopsis wound signalling, including jasmonic acid (JA), salicylic acid, auxin, and Ca2+. Here, we report on cross-talk of phytohormones with phosphoinositide signals not previously implicated in plant wound responses. Within 30 min of mechanical wounding of Arabidopsis rosette-leaves, the levels of the lipid-derived soluble inositolpolyphosphate, inositol 1,4,5-trisphosphate (InsP(3)), increased four to five-fold. Concomitantly, the precursor lipids, phosphatidylinositol 4,5-bisphosphate, phosphatidylinositol 4-phosphate and phosphatidylinositol transiently depleted, followed by re-synthesis after 30-60 min of stimulation. Increased InsP(3) levels with wounding coincided with JA increases over the first hours of stimulation. In dde2-2-mutant plants deficient in JA biosynthesis, no InsP(3) increase was observed upon wounding, indicating that JA was required for InsP(3) formation, and InsP(3) levels increased in wild-type plants challenged with sorbitol, increasing endogenous JA levels. In InsP 5-ptase plants with attenuated phosphoinositide signalling, the induction of wounding-inducible genes was diminished compared with wildtype plants, suggesting a role for phosphoinositide signalling in mediating plant wound responses. The gene-expression patterns suggest that phosphoinositides contribute to both JA-dependent and JA-independent aspects of wound signalling. Weight gain of Plutella xylostella caterpillars feeding on InsP 5-ptase plants was increased compared with that of caterpillars feeding on wild-type plants. The ecophysiological relevance of phosphoinositide signals in plant defense responses to herbivory is discussed in light of recent findings of inositolpolyphosphate involvement in phytohormone-receptor function.German Research Foundation [He3424/1-3
Phosphatidylinositol-4,5-bisphosphate influences Nt-Rac5-mediated cell expansion in pollen tubes of Nicotiana tabacum
No full textP>The regulation of pollen tube growth by the phospholipid phosphatidylinositol-4,5-bisphosphate (PtdIns(4,5)P(2)) is not well understood. The Arabidopsis genome encodes two type A phosphatidylinositol-4-phosphate (PI4P) 5-kinases, PIP5K10 and PIP5K11, which are exclusively expressed in pollen and produce PtdIns(4,5)P(2)in vitro. Fluorescence-tagged PIP5K10 and PIP5K11 localized to lateral subapical plasma membrane microdomains in tobacco pollen tubes in a pattern closely resembling the distribution of PtdIns(4,5)P(2,) with the exception of notably weaker association at the extreme apex. Overexpression of PIP5K10 or PIP5K11 in tobacco pollen tubes resulted in severe tip swelling and altered actin fine structure similar to that reported for overexpression of tobacco Nt-Rac5, a monomeric GTPase known to regulate the actin cytoskeleton. Increased sensitivity of Arabidopsis pip5k10 pip5k11 double mutant pollen tubes to Latrunculin B (LatB) further supports a role for type A PI4P 5-kinases in controlling the actin cytoskeleton. Despite the disruption of both its type A PI4P 5-kinases, the pip5k10 pip5k11 double mutant was fertile, indicating that one of the remaining type B PI4P 5-kinase isoforms might be functionally redundant with PIP5K10 and PIP5K11. Antagonistic effects of PIP5K11 and the Nt-Rac5-specific guanine nucleotide dissociation inhibitor, Nt-RhoGDI2, on tip swelling observed in coexpression-titration experiments indicate a link between PtdIns(4,5)P(2) and Rac-signaling in pollen tubes. The data suggest that type A PI4P 5-kinases influence the actin cytoskeleton in pollen tubes in part by counteracting Nt-RhoGDI2, possibly contributing to the control of the pool of plasma membrane-associated Nt-Rac5.German Research Foundation (DFG) [He3424/1
MarVis-Pathway: integrative and exploratory pathway analysis of non-targeted metabolomics data
No full textA central aim in the evaluation of non-targeted metabolomics data is the detection of intensity patterns that differ between experimental conditions as well as the identification of the underlying metabolites and their association with metabolic pathways. In this context, the identification of metabolites based on non-targeted mass spectrometry data is a major bottleneck. In many applications, this identification needs to be guided by expert knowledge and interactive tools for exploratory data analysis can significantly support this process. Additionally, the integration of data from other omics platforms, such as DNA microarray-based transcriptomics, can provide valuable hints and thereby facilitate the identification of metabolites via the reconstruction of related metabolic pathways. We here introduce the MarVis-Pathway tool, which allows the user to identify metabolites by annotation of pathways from cross-omics data. The analysis is supported by an extensive framework for pathway enrichment and meta-analysis. The tool allows the mapping of data set features by ID, name, and accurate mass, and can incorporate information from adduct and isotope correction of mass spectrometry data. MarVis-Pathway was integrated in the MarVis-Suite (http://marvis.gobics.de), which features the seamless highly interactive filtering, combination, clustering, and visualization of omics data sets. The functionality of the new software tool is illustrated using combined mass spectrometry and DNA microarray data. This application confirms jasmonate biosynthesis as important metabolic pathway that is upregulated during the wound response of Arabidopsis plants
Die Rolle von Phosphoinositol-Signalen in der Verwundungsantwort von Arabidopsis thaliana
No full textDie pflanzliche Wundantwort ist in der Verteidigung gegen Fraßfeinde von zentraler Bedeutung und daher streng reguliert. Das Isoleucinkonjugat der Jasmonsäure (JA-Ile) ist dabei eines der wichtigsten regulatorischen Moleküle. In dieser Dissertation wurden Phosphoinositide (PI), die vorher nicht als Wundsignale bekannt waren, untersucht und als neue aktive Komponenten des Signalnetzwerkes der pflanzlichen Verteidigungsantwort beschrieben. Transgene InsP 5-ptase-Pflanzen mit gestörter PI-Signalleitung zeigten abgeschwächte wundinduzierte Genexpression und verminderte Abwehr gegen Raupenfraß. Diese Ergebnisse zeigen, dass wundinduzierte Akkumulation von PI-Signalen für eine vollständige Wund- und Abwehrreaktion benötigt wird. Neben der abgeschwächten Abwehr zeigten InsP 5-ptase-Pflanzen eine JA-Ile-Akkumulazion in ähnlichen Mustern wie JA-insensitive coi1-Mutanten. Diese Daten deuten darauf hin, dass InsP 5-ptase-Pflanzen wenigstens teilweise insensitiv gegenüber JA-Ile sind. Um das Zusammenspiel von PI-Signalen und JA-Ile-Wahrnehmung zu erklären, wurde der Arabidopsis JA-Ile-Rezeptor COI1 mit dem Auxin-Rezeptor TIR1, der ein Inositol-Hexakisphosphat (InsP6) als Kofaktor enthält, verglichen. Aufgrund der strukturellen Ähnlichkeit zwischen COI1 und TIR1 wurde die Hypothese getestet, dass ein Inositolpolyphosphat-Kofaktor für die COI1-Funktion benötigt wird. COI1-Varianten, in denen putative Inositolpolyphosphat-koordinierende Aminosäuren gegen Alanine ausgetauscht wurden, zeigten in Yeast-two-hybrid-Interaktionstests eine abgeschwächte Interaktion mit dem COI1-Zielprotein, JAZ9. Übereinstimmend damit zeigten die gleichen COI1-Varianten eine verminderte Fähigkeit, Jasmonat-vermittelte Prozesse, wie Inhibierung von Wurzelwachstum oder Schotenentwicklung, in Arabidopsis coi1-Mutanten wiederherzustellen. Weitere Yeast-two-hybrid-Interaktionstest mit Wildtyp-COI1 in einem ipk1Δ-Hefestamm mit erhöhten Inositolpentakisphosphat (InsP5)- und erniedrigten InsP6-Niveaus zeigten eine verstärkte COI1/JAZ9-Interaktion. Übereinstimmend mit diesen Daten zeigten Arabidopsis ipk1-1-Mutanten, ebenfalls mit erhöhten InsP5- und erniedrigten InsP6-Niveaus, eine verstärkte Abwehr durch COI1-vermittelte Prozesse, wie wundinduzierte Genexpression und Verteidigung gegen Raupenfraß, oder Inhibierung von Wurzelwachstum durch Jasmonat. Die Kombination der Daten aus Hefe- und Arabidopsis-Experimenten zeigt, dass ein Inositolpolyphosphat, wahrscheinlic h InsP5, für die COI1-Funktion in Arabidopsis benötigt wird. Experimente mit Salicylsäure (SA)-defizienten Arabidopsis Mutanten deuteten eine weiteres Zusammenspiel zwischen SA- und PI-Signalen in der Wundantwort an, was PI-Signalen eine tragende Rolle als zentrale Komponente des regulatorischen Netzwerkes der Arabidopsis-Wundantwort zuweist.Plant responses to wounding are of central importance during defence against herbivores and therefore tightly regulated. Hereby the isoleucin conjugate of jasmonic acid (JA-Ile) is a major regulatory molecule. In this thesis, phosphoinositide (PI) signals not previously implicated in plant wound responses have been studied and are introduced as new components active in the signalling network regulating plant defence responses. Transgenic Arabidopsis InsP 5-ptase plants that are attenuated in PI signalling exhibited decreased wound-induced gene expression as well as reduced defence against caterpillar feeding. These results indicate that wound-induced accumulation of PI signals is required for full wounding and defence responses. Besides their attenuated defence, InsP 5-ptase plants accumulated JA-Ile in a pattern also found for JA-insensitive Arabidopsis coi1 mutants. These data suggest that InsP 5-ptase plants are partially insensitive towards JA-Ile. To explain the interdependency of PI-derived signals and JA-Ile perception, the Arabidopsis JA-Ile receptor, COI1, was compared with the auxin receptor, TIR1, which contains an inositol hexakisphosphate (InsP6) cofactor. Based on the structural similarity of COI1 and TIR1 the possibility was explored that an inositol polyphosphate cofactor is required for COI1 function. COI1 variants, in which putative inositol polyphosphate coordinating amino acids were exchanged for alanines, exhibited reduced interaction with the COI1 target, JAZ9, in yeast two-hybrid tests. Consistent with the yeast two-hybrid data, the same COI1 variants displayed reduced capability to rescue jasmonate-mediated root growth inhibition or silique development in Arabidopsis coi1 mutants. Further yeast two-hybrid tests using wild type COI1 in an ipk1Δ yeast strain with increased levels of inositol pentakisphosphate (InsP5) and reduced levels of InsP6 indicated an enhanced COI1/JAZ9 interaction. Consistent with these findings, Arabidopsis ipk1-1 mutants, also with increased InsP5 and reduced InsP6 levels, showed increased defensive capabilities via COI1-mediated processes, including wound-induced gene expression, defence against caterpillars, or root growth inhibition by jasmonate. The combined data from yeast and Arabidopsis experiments indicate that an inositol polyphosphate and likely InsP5 is required for COI1 function in Arabidopsis. Experiments on salicylic acid (SA)-deficient Arabidopsis mutants suggest a furthe r interrelation between SA and PI signals in wounding responses, establishing PI-derived signals as a central component of the regulatory network controlling Arabidopsis responses to wounding
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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