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Identification of novel in vivo MAP kinase substrates in Arabidopsis thaliana through use of tandem metal oxide affinity chromatography.

ABSTRACT: Mitogen-activated protein kinase (MPK) cascades are important for eukaryotic signal transduction. They convert extracellular stimuli (e.g. some hormones, growth factors, cytokines, microbe- or damage-associated molecular patterns) into intracellular responses while at the same time amplifying the transmitting signal. By doing so, they ensure proper performance, and eventually survival, of a given organism, for example in times of stress. MPK cascades function via reversible phosphorylation of cascade components MEKKs, MEKs, and MPKs. In plants the identity of most MPK substrates remained elusive until now. Here, we provide a robust and powerful approach to identify and quantify, with high selectivity, site-specific phosphorylation of MPK substrate candidates in the model plant Arabidopsis thaliana. Our approach represents a two-step chromatography combining phosphoprotein enrichment using Al(OH)(3)-based metal oxide affinity chromatography, tryptic digest of enriched phosphoproteins, and TiO(2)-based metal oxide affinity chromatography to enrich phosphopeptides from complex protein samples. When applied to transgenic conditional gain-of-function Arabidopsis plants supporting in planta activation of MPKs, the approach allows direct measurement and quantification ex vivo of site-specific phosphorylation of several reported and many yet unknown putative MPK substrates in just a single experiment.

SUBMITTER: Hoehenwarter W

PROVIDER: S-EPMC3567860 | biostudies-literature | 2013 Feb

REPOSITORIES: biostudies-literature

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Identification of novel in vivo MAP kinase substrates in Arabidopsis thaliana through use of tandem metal oxide affinity chromatography.

Hoehenwarter Wolfgang W Thomas Martin M Nukarinen Ella E Egelhofer Volker V Röhrig Horst H Weckwerth Wolfram W Conrath Uwe U Beckers Gerold J M GJ

Molecular & cellular proteomics : MCP 20121120 2

Mitogen-activated protein kinase (MPK) cascades are important for eukaryotic signal transduction. They convert extracellular stimuli (e.g. some hormones, growth factors, cytokines, microbe- or damage-associated molecular patterns) into intracellular responses while at the same time amplifying the transmitting signal. By doing so, they ensure proper performance, and eventually survival, of a given organism, for example in times of stress. MPK cascades function via reversible phosphorylation of ca ...[more]

PMID: 23172892

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Project description:Plant Growth and Treatment. Seedlings of Arabidopsis thaliana GVG::FLAG-NtMEK2DD were grown in 50 ml of half-strength Murashige and Skoog medium at 22°C under continuous light (70 µE/m2/sec). Twelve-day-old seedlings were treated with DEX (1 µM) or ethanol (control) and collected 6 h after treatment. Protein Extraction and MOAC Enrichment of Phosphoproteins. Protein extraction from seedlings and enrichment of phosphoprotein. The concentration of protein in extracts was determined using the Bio-Rad protein assay kit with BSA as the standard. Western Blotting Analysis and Immunodetection. Protein samples were subjected to SDS-PAGE, transferred to nitrocellulose, and used for immunodetection. Mouse monoclonal anti-Flag M2 antibodies were purchased from Sigma-Aldrich; all other antibodies were from New England Biolabs. Chemiluminescence detection of antigen-antibody complexes was done with Immobilon™ Western substrate (Millipore). Enrichment of Phosphopeptides by MOAC. For in-solution protein digestion, total proteins or MOAC-enriched phosphoproteins were predigested for 5 h with endoproteinase Lys-C (1/100 w/w) followed by trypsin digestion (Poroszyme immobilized trypsin (1/100 v/w)) overnight. Protein digests were desalted using a SPEC C-18 96-well plate (Varian) according to the manufacturer’s instructions. TiO2 beads were purchased from Glygen Inc. Mass Spectrometry and Protein Identification. Peptides were analyzed using an Orbitrap XL mass spectrometer (Thermo Scientific). Chromatography was performed using a Chromolith CapRod C18 monolithic column with 0.1% (v/v) formic acid (FA) in ultrapure H2O and 0.1% (v/v) FA in 90% (v/v) acetonitrile (ACN) in ultrapure H20 as mobile phases and a gradient from 10% to 35% organic phase in 120 min with a flow rate of 500 nl/min. Multistage activation/pseudoMS3 was enabled for acquisition of CID tandem MS (MS/MS) mass spectra of phosphopeptides with a neutral loss mass list of 97.97, 48.999, 32.66 and 24.49 Da. Database search was performed with the Proteome Discoverer Software version 1.2. using the SEQUEST algorithm.

Project description:BackgroundIn plants, the shoot apical meristem (SAM) has two main functions, involving the production of all aerial organs on the one hand and self-maintenance on the other, allowing the production of organs during the entire post-embryonic life of the plant. Transcription factors, microRNA, hormones, peptides and forces have been involved in meristem function. Whereas phosphatidylinositol phosphates (PIPs) have been involved in almost all biological functions, including stem cell maintenance and organogenesis in animals, the processes in meristem biology to which PIPs contribute still need to be delineated.ResultsUsing biosensors for PI4P and PI(4,5)P2, the two most abundant PIPs at the plasma membrane, we reveal that meristem functions are associated with a stereotypical PIP tissue-scale pattern, with PI(4,5)P2 always displaying a more clear-cut pattern than PI4P. Using clavata3 and pin-formed1 mutants, we show that stem cell maintenance is associated with reduced levels of PIPs. In contrast, high PIP levels are signatures for organ-meristem boundaries. Interestingly, this pattern echoes that of cortical microtubules and stress anisotropy at the meristem. Using ablations and pharmacological approaches, we further show that PIP levels can be increased when the tensile stress pattern is altered. Conversely, we find that katanin mutant meristems, with increased isotropy of microtubule arrays and slower response to mechanical perturbations, exhibit reduced PIP gradients within the SAM. Comparable PIP pattern defects were observed in phospholipase A3β overexpressor lines, which largely phenocopy katanin mutants at the whole plant level.ConclusionsUsing phospholipid biosensors, we identified a stereotypical PIP accumulation pattern in the SAM that negatively correlates with stem cell maintenance and positively correlates with organ-boundary establishment. While other cues are very likely to contribute to the final PIP pattern, we provide evidence that the patterns of PIP, cortical microtubules and mechanical stress are positively correlated, suggesting that the PIP pattern, and its reproducibility, relies at least in part on the mechanical status of the SAM.

Dataset Information

Identification of novel in vivo MAP kinase substrates in Arabidopsis thaliana through use of tandem metal oxide affinity chromatography.

Publications

Identification of novel in vivo MAP kinase substrates in Arabidopsis thaliana through use of tandem metal oxide affinity chromatography.

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