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Publikation

Furlan, G., Nakagami, H., Eschen-Lippold, L., Jiang, X., Majovsky, P., Kowarschik, K., Hoehenwarter, W., Lee, J. & Trujillo, M. Changes in PUB22 ubiquitination modes triggered by MITOGEN-ACTIVATED PROTEIN KINASE3 dampen the immune response Plant Cell 29, 726-745, (2017) DOI: 10.1105/tpc.16.00654

Crosstalk between post-translational modifications such as ubiquitination and phosphorylation play key roles in controlling the duration and intensity of signalling events to ensure cellular homeostasis. However, the molecular mechanisms underlying the regulation of negative feedback loops remain poorly understood. Here we uncover a pathway in Arabidopsis thaliana by which a negative feedback loop involving the E3 ubiquitin ligase PUB22 that dampens the immune response is triggered by MITOGEN-ACTIVATED PROTEIN KINASE3 (MPK3), best known for its function in the activation of signalling. PUB22's stability is controlled by MPK3-mediated phosphorylation of residues localized in and adjacent to the E2 docking domain. We show that phosphorylation is critical for stabilization by inhibiting PUB22 oligomerization and thus autoubiquitination. The activity switch allows PUB22 to dampen the immune response. This regulatory mechanism also suggests that autoubiquitination, which is inherent to most single unit E3s in vitro, can function as a self-regulatory mechanism in vivo. 
Publikation

Winkler, M., Niemeyer, M., Hellmuth, A., Janitza, P., Christ, G., Samodelov, S. L., Wilde, V., Majovsky, P., Trujillo, M., Zurbriggen, M. D., Hoehenwarter, W., Quint, M. & Calderón Villalobos, L. I. A. Variation in auxin sensing guides AUX/IAA transcriptional repressor ubiquitylation and destruction. Nature Commun. 8, 15706, (2017) DOI: 10.1038/ncomms15706

Auxin is a small molecule morphogen that bridges SCFTIR1/AFB-AUX/IAA co-receptor interactions leading to ubiquitylation and proteasome-dependent degradation of AUX/IAA transcriptional repressors. Here, we systematically dissect auxin sensing by SCFTIR1-IAA6 and SCFTIR1-IAA19 co-receptor complexes, and assess IAA6/IAA19 ubiquitylation in vitro and IAA6/IAA19 degradation in vivo. We show that TIR1-IAA19 and TIR1-IAA6 have distinct auxin affinities that correlate with ubiquitylation and turnover dynamics of the AUX/IAA. We establish a system to track AUX/IAA ubiquitylation in IAA6 and IAA19 in vitro and show that it occurs in flexible hotspots in degron-flanking regions adorned with specific Lys residues. We propose that this signature is exploited during auxin-mediated SCFTIR1-AUX/IAA interactions. We present evidence for an evolving AUX/IAA repertoire, typified by the IAA6/IAA19 ohnologues, that discriminates the range of auxin concentrations found in plants. We postulate that the intrinsic flexibility of AUX/IAAs might bias their ubiquitylation and destruction kinetics enabling specific auxin responses.
Publikationen in Druck

Rajaraman, J., Douchkov, D., Lueck, S., Hensel, G., Nowara, D., Pogoda, M., Rutten, T., Meitzel, T., Hoefle, C., Hueckelhoven, R., Klinkenberg, J., Trujillo, M., Bauer, E., Schmutzer, T., Himmelbach, A., Mascher, M., Lazzari, B., Stein, N., Kumlehn, J. & Schweizer, P. The partial duplication of an E3-ligase gene in Triticeae species mediates resistance to powdery mildew fungi.  bioRxiv (2017) DOI: 10.1101/190728

In plant-pathogen interactions, components of the plant ubiquitination machinery are preferred targets of pathogen-encoded effectors suppressing defense responses or co-opting host cellular functions for accommodation. Here, we employed transient and stable gene silencing- and over-expression systems in Hordeum vulgare (barley) to study the function of HvARM1 (for H. vulgare Armadillo 1), a partial gene duplicate of the U-box/armadillo-repeat E3 ligase HvPUB15 (for H. vulgare Plant U-Box 15). The partial ARM1 gene was derived from an ancient gene-duplication event in a common ancestor of the Triticeae tribe of grasses comprising the major crop species H. vulgare, Triticum aestivum and Secale cereale. The barley gene HvARM1 contributed to quantitative host as well as nonhost resistance to the biotrophic powdery mildew fungus Blumeria graminis, and allelic variants were found to be associated with powdery mildew-disease severity. Both HvPUB15 and HvARM1 proteins interacted in yeast and plant cells with the susceptibility-related, plastid- localized barley homologs of THF1 (for Thylakoid formation 1 ) and of ClpS1 (for Clp-protease adaptor S1) of Arabidopsis thaliana. The results suggest a neo-functionalization HvARM1 to increase resistance against powdery mildew and provide a link to plastid function in susceptibility to biotrophic pathogen attack.
Publikation

Matsui, H., Nomura, Y., Egusa, M., Hamada, T., Hyon, G.-S., Kaminaka, H., Watanabe, Y., Ueda, T., Trujillo, M., Shirasu, K. & Nakagami, H. The GYF domain protein PSIG1 dampens the induction of cell death during plant-pathogen interactions. PLoS Genet. 13(10), e1007037, (2017) DOI: 10.1371/journal.pgen.1007037

The induction of rapid cell death is an effective strategy for plants to restrict biotrophic and hemi-biotrophic pathogens at the infection site. However, activation of cell death comes at a high cost, as dead cells will no longer be available for defense responses nor general metabolic processes. In addition, necrotrophic pathogens that thrive on dead tissue, take advantage of cell death-triggering mechanisms. Mechanisms by which plants solve this conundrum remain described. Here, we identify PLANT SMY2-TYPE ILE-GYF DOMAIN-CONTAINING PROTEIN 1 (PSIG1) and show that PSIG1 helps to restrict cell death induction during pathogen infection. Inactivation of PSIG1 does not result in spontaneous lesions, and enhanced cell death in psig1 mutants is independent of salicylic acid (SA) biosynthesis or reactive oxygen species (ROS) production. Moreover, PSIG1 interacts with SMG7, which plays a role in nonsense-mediated RNA decay (NMD), and the smg7-4 mutant allele mimics the cell death phenotype of the psig1 mutants. Intriguingly, the psig1 mutants display enhanced susceptibility to the hemi-biotrophic bacterial pathogen. These findings point to the existence and importance of the SA- and ROS-independent cell death constraining mechanism as a part of the plant immune system.
Publikationen in Druck

Kowarschik, K., Hoehenwarter, W., Marillonnet, S. & Trujillo, M.  UbiGate: a synthetic biology toolbox to analyse ubiquitination. New Phytol. (2017) DOI: 10.1111/nph.14900

   Ubiquitination is mediated by an enzymatic cascade that results in the modification of substrate proteins, redefining their fate. This post-translational modification is involved in most cellular processes, yet its analysis faces manifold obstacles due to its complex and ubiquitous nature. Reconstitution of the ubiquitination cascade in bacterial systems circumvents several of these problems and was shown to faithfully recapitulate the process.
    Here, we present UbiGate − a synthetic biology toolbox, together with an inducible bacterial expression system – to enable the straightforward reconstitution of the ubiquitination cascades of different organisms in Escherichia coli by ‘Golden Gate’ cloning.
    This inclusive toolbox uses a hierarchical modular cloning system to assemble complex DNA molecules encoding the multiple genetic elements of the ubiquitination cascade in a predefined order, to generate polycistronic operons for expression.
    We demonstrate the efficiency of UbiGate in generating a variety of expression elements to reconstitute autoubiquitination by different E3 ligases and the modification of their substrates, as well as its usefulness for dissecting the process in a time- and cost-effective manner.
Bücher und Buchkapitel

Furlan, G. & Trujillo, M. In vitro ubiquitination activity assays in plant immune responses.. In: Plant Pattern Recognition Receptors: Methods and Protocols (L. Shan, et al.). Meth. Mol. Biol. 1578, 109-121, (2017) ISBN: 978-1-4939-6859-6 DOI: 10.1007/978-1-4939-6859-6_8

Ubiquitination is a central posttranslational modification that impinges on the fate of proteins. While attachment of K48-linked chains onto soluble proteins marks them for proteolysis via the 26S proteasome, mono-ubiquitination or K63-linked chains result in the endocytosis and sorting through the endomembrane system of integral membrane proteins, such as pattern recognition receptors. In vitro ubiquitination assays allow the biochemical analysis of all individual components of the ubiquitination machinery and its potential substrates. Here, we describe how to reconstitute the ubiquitination cascade in vitro and detail different variations of the assay, the required controls and how to interpret the obtained results.

Bücher und Buchkapitel

Trujillo, M. Analysis of the lmmunity-Related Oxidative Bursts by a Luminol-Based Assay. In: Environmental Responses in Plants Meth Mol Biol 1398, 323-329, (2016) ISBN: 978-1-4939-3354-9 DOI: 10.1007/978-1-4939-3356-3_26

The rapid production of reactive oxygen species (ROS) in response to biotic and abiotic cues is a conserved hallmark of plant responses. The detection and quantification of ROS generation during immune responses is an excellent readout to analyze signaling triggered by the perception of pathogens. The assay described here is easy to employ and versatile, allowing its use in a multitude of variations. For example, ROS production can be analyzed using different tissues including whole seedlings, roots, leaves, protoplasts, and cultured cells, which can originate from different ecotypes or mutants. Samples can be tested in combination with any ROS-inducing elicitors, such as the FLS2-activating peptide flg22, but also lipids or even abiotic stresses. Furthermore, early (PAMP-triggered) and late (effector-triggered) ROS production induced by virulent and avirulent bacteria, respectively, can also be assayed.

Publikation

Majovsky, P., Naumann, C., Lee, C.-W., Lassowskat, I., Trujillo, M., Dissmeyer, N. & Hoehenwarter, W. Targed proteomics analysis of protein degradation in plant signaling on an LTO-Orbitrap mass spectrometer J Proteome Res 13, 4246–4258, (2014) DOI: 10.1021/pr500164j

Targeted proteomics has become increasingly popular recently because of its ability to precisely quantify selected proteins in complex cellular backgrounds. Here, we demonstrated the utility of an LTQ-Orbitrap Velos Pro mass spectrometer in targeted parallel reaction monitoring (PRM) despite its unconventional dual ion trap configuration. We evaluated absolute specificity (>99%) and sensitivity (100 amol on column in 1 μg of total cellular extract) using full and mass range scans as survey scans together with data-dependent (DDA) and targeted MS/MS acquisition. The instrument duty cycle was a critical parameter limiting sensitivity, necessitatingpeptide retention time scheduling. We assessed synthetic peptide and recombinant peptide standards to predict or experimentally determine target peptide retention times. We applied optimized PRM to protein degradation in signaling regulation, an area that is receiving increased attention in plant physiology. We quantified relative abundance of selected proteins in plants that are mutant for enzymatic components of the N-end rule degradation (NERD) pathway such as the two tRNA-arginyl-transferases ATE1 and ATE2 and the two E3 ubiquitin ligases PROTEOLYSIS1 and 6. We found a number of upregulated proteins, which might represent degradation targets. We also targeted FLAGELLIN SENSITIVE2 (FLS2), a pattern recognition receptor responsible for pathogen sensing, in ubiquitin ligase mutants to assay the attenuation of plant immunity by degradation of the receptor.

Publikation

Dörmann, P., Kim, H., Ott,T., Schulze-Lefert, P., Trujillo, M., Wewer, V. & Hückelhoven, R. Cell-autonomous defense, re-organization and trafficking of membranes in plant–microbe interaction New Phytologist 204, 815–822, (2014) DOI: 10.1111/nph.12978

Plant cells dynamically change their architecture and molecular composition following encounters with beneficial or parasitic microbes, a process referred to as host cell reprogramming. Cell-autonomous defense reactions are typically polarized to the plant cell periphery underneath microbial contact sites, including de novo cell wall biosynthesis. Alternatively, host cell reprogramming converges in the biogenesis of membrane-enveloped compartments for accommodation of beneficial bacteria or invasive infection structures of filamentous microbes. Recent advances have revealed that, in response to microbial encounters, plasma membrane symmetry is broken, membrane tethering and SNARE complexes are recruited, lipid composition changes and plasma membrane-to-cytoskeleton signaling is activated, either for pre-invasive defense or for microbial entry. We provide a critical appraisal on recent studies with a focus on how plant cells re-structure membranes and the associated cytoskeleton in interactions with microbial pathogens, nitrogen-fixing rhizobia and mycorrhiza fung

Publikation

Stegmann, M., Anderson, R. G., Westphal, L., Rosahl, S., McDowell, J. M. & Trujillo, M. The exocyst subunit Exo70B1 is involved in the immune response of Arabidopsis thaliana to different pathogens and cell death Plant Signal. & Behavior 8, e27421, (2013) DOI: org/10.4161/psb.27421

Components of the vesicle trafficking machinery are central to the immune response in plants. The role of vesicle trafficking during pre-invasive penetration resistance has been well documented. However, emerging evidence also implicates vesicle trafficking in early immune signaling. Here we report that Exo70B1, a subunit of the exocyst complex which mediates early tethering during exocytosis is involved in resistance. We show that exo70B1 mutants display pathogen-specific immuno-compromised phenotypes. We also show that exo70B1 mutants display lesion-mimic cell death, which in combination with the reduced responsiveness to pathogen-associated molecular patterns (PAMPs) results in complex immunity-related phenotypes.

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