Competition between two HUSH complexes orchestrates the immune response to retroelement invasion.

The human silencing hub (HUSH) preserves genome integrity through the epigenetic repression of invasive genetic elements. However, despite our understanding of HUSH as an obligate complex of three subunits, only loss of MPP8 or Periphilin, but not TASOR, triggers interferon signaling following derepression of endogenous retroelements. Here, we resolve this paradox by characterizing a second HUSH complex that shares MPP8 and Periphilin but assembles around TASOR2, an uncharacterized paralog of TASOR. Whereas HUSH represses LINE-1 retroelements marked by the repressive histone modification H3K9me3, HUSH2 is recruited by the transcription factor IRF2 to repress interferon-stimulated genes. Mechanistically, HUSH-mediated retroelement silencing sequesters the limited pool of the shared subunits MPP8 and Periphilin, preventing TASOR2 from forming HUSH2 complexes and hence relieving the HUSH2-mediated repression of interferon-stimulated genes. Thus, competition between two HUSH complexes intertwines retroelement silencing with the induction of an immune response, coupling epigenetic and immune aspects of genome defense.

Separating Golgi Proteins from Cis to Trans Reveals Underlying Properties of Cisternal Localization.

The order of enzymatic activity across Golgi cisternae is essential for complex molecule biosynthesis. However, an inability to separate Golgi cisternae has meant that the cisternal distribution of most resident proteins, and their underlying localization mechanisms, are unknown. Here, we exploit differences in surface charge of intact cisternae to perform separation of early to late Golgi subcompartments. We determine protein and glycan abundance profiles across the Golgi; over 390 resident proteins are identified, including 136 new additions, with over 180 cisternal assignments. These assignments provide a means to better understand the functional roles of Golgi proteins and how they operate sequentially. Protein and glycan distributions are validated in vivo using high-resolution microscopy. Results reveal distinct functional compartmentalization among resident Golgi proteins. Analysis of transmembrane proteins shows several sequence-based characteristics relating to pI, hydrophobicity, Ser abundance, and Phe bilayer asymmetry that change across the Golgi. Overall, our results suggest that a continuum of transmembrane features, rather than discrete rules, guide proteins to earlier or later locations within the Golgi stack.

Mass spectrometry approaches to study plant endomembrane trafficking.

Intracellular proteins reside in highly controlled microenvironments in which they perform context specific functions. Trafficking pathways have evolved that enable proteins to be precisely delivered to the correct location but also to re-locate in response to environmental perturbation. Trafficking of membrane proteins to their correct endomembrane location is especially important to enable them to carry out their function. Although a considerable amount of knowledge about membrane protein trafficking in plants has been delivered by years of dedicated research, there are still significant gaps in our understanding of this process. Further knowledge of endomembrane trafficking is dependent on thorough characterization of the subcellular components that constitute the endomembrane system. Such studies are challenging for a number of reasons including the complexity of the plant endomembrane system, inability to purify individual constituents, discrimination protein cargo for full time residents of compartments, and the fact that many proteins function at more than one location. In this review, we describe the components of the secretory pathway and focus on how mass spectrometry based proteomics methods have helped elucidation of this pathway. We demonstrate that the combination of targeted and untargeted approaches is allowing research into new areas of the secretory pathway investigation. Finally we describe new enabling technologies that will impact future studies in this area.

Multiple marker abundance profiling: combining selected reaction monitoring and data-dependent acquisition for rapid estimation of organelle abundance in subcellular samples.

Measuring changes in protein or organelle abundance in the cell is an essential, but challenging aspect of cell biology. Frequently-used methods for determining organelle abundance typically rely on detection of a very few marker proteins, so are unsatisfactory. In silico estimates of protein abundances from publicly available protein spectra can provide useful standard abundance values but contain only data from tissue proteomes, and are not coupled to organelle localization data. A new protein abundance score, the normalized protein abundance scale (NPAS), expands on the number of scored proteins and the scoring accuracy of lower-abundance proteins in Arabidopsis. NPAS was combined with subcellular protein localization data, facilitating quantitative estimations of organelle abundance during routine experimental procedures. A suite of targeted proteomics markers for subcellular compartment markers was developed, enabling independent verification of in silico estimates for relative organelle abundance. Estimation of relative organelle abundance was found to be reproducible and consistent over a range of tissues and growth conditions. In silico abundance estimations and localization data have been combined into an online tool, multiple marker abundance profiling, available in the SUBA4 toolbox (http://suba.live).

In-depth characterization of the tomato fruit pericarp proteome.

Since the genome of Solanum lycopersicum L. was published in 2012, some studies have explored its proteome although with a limited depth. In this work, we present an extended characterization of the proteome of the tomato pericarp at its ripe red stage. Fractionation of tryptic peptides generated from pericarp proteins by off-line high-pH reverse-phase phase chromatography in combination with LC-MS/MS analysis on a Fisher Scientific Q Exactive and a Sciex Triple-TOF 6600 resulted in the identification of 8588 proteins with a 1% FDR both at the peptide and protein levels. Proteins were mapped through GO and KEGG databases and a large number of the identified proteins were associated with cytoplasmic organelles and metabolic pathways categories. These results constitute one of the most extensive proteome datasets of tomato so far and provide an experimental confirmation of the existence of a high number of theoretically predicted proteins. All MS data are available in the ProteomeXchange repository with the dataset identifiers PXD004947 and PXD004932.

Spectral Libraries for SWATH-MS Assays for Drosophila melanogaster and Solanum lycopersicum.

Quantitative proteomics methods have emerged as powerful tools for measuring protein expression changes at the proteome level. Using MS-based approaches, it is now possible to routinely quantify thousands of proteins. However, prefractionation of the samples at the protein or peptide level is usually necessary to go deep into the proteome, increasing both MS analysis time and technical variability. Recently, a new MS acquisition method named SWATH is introduced with the potential to provide good coverage of the proteome as well as a good measurement precision without prior sample fractionation. In contrast to shotgun-based MS however, a library containing experimental acquired spectra is necessary for the bioinformatics analysis of SWATH data. In this study, spectral libraries for two widely used models are built to study crop ripening or animal embryogenesis, Solanum lycopersicum (tomato) and Drosophila melanogaster, respectively. The spectral libraries comprise fragments for 5197 and 6040 proteins for S. lycopersicum and D. melanogaster, respectively, and allow reproducible quantification for thousands of peptides per MS analysis. The spectral libraries and all MS data are available in the MassIVE repository with the dataset identifiers MSV000081074 and MSV000081075 and the PRIDE repository with the dataset identifiers PXD006493 and PXD006495.

Free-Flow Electrophoresis of Plasma Membrane Vesicles Enriched by Two-Phase Partitioning Enhances the Quality of the Proteome from Arabidopsis Seedlings.

The plant plasma membrane is the interface between the cell and its environment undertaking a range of important functions related to transport, signaling, cell wall biosynthesis, and secretion. Multiple proteomic studies have attempted to capture the diversity of proteins in the plasma membrane using biochemical fractionation techniques. In this study, two-phase partitioning was combined with free-flow electrophoresis to produce a population of highly purified plasma membrane vesicles that were subsequently characterized by tandem mass spectroscopy. This combined high-quality plasma membrane isolation technique produced a reproducible proteomic library of over 1000 proteins with an extended dynamic range including plasma membrane-associated proteins. The approach enabled the detection of a number of putative plasma membrane proteins not previously identified by other studies, including peripheral membrane proteins. Utilizing multiple data sources, we developed a PM-confidence score to provide a value indicating association to the plasma membrane. This study highlights over 700 proteins that, while seemingly abundant at the plasma membrane, are mostly unstudied. To validate this data set, we selected 14 candidates and transiently localized 13 to the plasma membrane using a fluorescent tag. Given the importance of the plasma membrane, this data set provides a valuable tool to further investigate important proteins. The mass spectrometry data are available via ProteomeXchange, identifier PXD001795.

Preparation of Highly Enriched ER Membranes Using Free-Flow Electrophoresis.

Free-flow electrophoresis (FFE) is a technique for separation of proteins, peptides, organelles, and cells. With zone electrophoresis (ZE-FFE), organelles are separated according to surface charge. The ER is the only remaining major cellular compartment in Arabidopsis not to have been isolated using density centrifugation, immune-isolation, or any other method previously applied to purification of plant membranes. By using continuous-flow electrophoresis, ER vesicles of similar surface charge, which may have been fragmented during cell lysis, can be focused. A large portion of these vesicles are of sufficiently different surface charge that separation from the majority of Golgi and other contaminants is possible. Here we adapt an earlier ZE-FFE Golgi isolation protocol for the isolation of highly pure ER vesicles and for tracking the migration of peripheral ER vesicles. Isolating ER vesicles of homogeneous surface charge allows multi-omic analyses to be performed on the ER. This facilitates investigations into structure-function relationships within the ER.

Isolation and proteomic characterization of the Arabidopsis Golgi defines functional and novel components involved in plant cell wall biosynthesis.

The plant Golgi plays a pivotal role in the biosynthesis of cell wall matrix polysaccharides, protein glycosylation, and vesicle trafficking. Golgi-localized proteins have become prospective targets for reengineering cell wall biosynthetic pathways for the efficient production of biofuels from plant cell walls. However, proteomic characterization of the Golgi has so far been limited, owing to the technical challenges inherent in Golgi purification. In this study, a combination of density centrifugation and surface charge separation techniques have allowed the reproducible isolation of Golgi membranes from Arabidopsis (Arabidopsis thaliana) at sufficiently high purity levels for in-depth proteomic analysis. Quantitative proteomic analysis, immunoblotting, enzyme activity assays, and electron microscopy all confirm high purity levels. A composition analysis indicated that approximately 19% of proteins were likely derived from contaminating compartments and ribosomes. The localization of 13 newly assigned proteins to the Golgi using transient fluorescent markers further validated the proteome. A collection of 371 proteins consistently identified in all replicates has been proposed to represent the Golgi proteome, marking an appreciable advancement in numbers of Golgi-localized proteins. A significant proportion of proteins likely involved in matrix polysaccharide biosynthesis were identified. The potential within this proteome for advances in understanding Golgi processes has been demonstrated by the identification and functional characterization of the first plant Golgi-resident nucleoside diphosphatase, using a yeast complementation assay. Overall, these data show key proteins involved in primary cell wall synthesis and include a mixture of well-characterized and unknown proteins whose biological roles and importance as targets for future research can now be realized.

Proteomic analysis of circulating immune cells identifies cellular phenotypes associated with COVID-19 severity.

Certain serum proteins, including C-reactive protein (CRP) and D-dimer, have prognostic value in patients with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Nonetheless, these factors are non-specific, providing limited mechanistic insight into the peripheral blood mononuclear cell (PBMC) populations that drive the pathogenesis of severe COVID-19. To identify cellular phenotypes associated with disease, we performed a comprehensive, unbiased analysis of total and plasma-membrane PBMC proteomes from 40 unvaccinated individuals with SARS-CoV-2, spanning the whole disease spectrum. Combined with RNA sequencing (RNA-seq) and flow cytometry from the same donors, we define a comprehensive multi-omic profile for each severity level, revealing that immune-cell dysregulation progresses with increasing disease. The cell-surface proteins CEACAMs1, 6, and 8, CD177, CD63, and CD89 are strongly associated with severe COVID-19, corresponding to the emergence of atypical CD3+CD4+CEACAM1/6/8+CD177+CD63+CD89+ and CD16+CEACAM1/6/8+ mononuclear cells. Utilization of these markers may facilitate real-time patient assessment by flow cytometry and identify immune populations that could be targeted to ameliorate immunopathology.

Alternative pathways of dehydroascorbic acid degradation in vitro and in plant cell cultures: novel insights into vitamin C catabolism.

L-Ascorbate catabolism involves reversible oxidation to DHA (dehydroascorbic acid), then irreversible oxidation or hydrolysis. The precursor-product relationships and the identity of several major DHA breakdown products remained unclear. In the presence of added H2O2, DHA underwent little hydrolysis to DKG (2,3-dioxo-L-gulonate). Instead, it yielded OxT (oxalyl L-threonate), cOxT (cyclic oxalyl L-threonate) and free oxalate (~6:1:1), essentially simultaneously, suggesting that all three product classes independently arose from one reactive intermediate, proposed to be cyclic-2,3-O-oxalyl-L-threonolactone. Only with plant apoplastic esterases present were the esters significant precursors of free oxalate. Without added H2O2, DHA was slowly hydrolysed to DKG. Downstream of DKG was a singly ionized dicarboxy compound (suggested to be 2-carboxy-L-xylonolactone plus 2-carboxy-L-lyxonolactone), which reversibly de-lactonized to a dianionic carboxypentonate. Formation of these lactones and acid was minimized by the presence of residual unreacted ascorbate. In vivo, the putative 2-carboxy-L-pentonolactones were relatively stable. We propose that DHA is a branch-point in ascorbate catabolism, being either oxidized to oxalate and its esters or hydrolysed to DKG and downstream carboxypentonates. The oxidation/hydrolysis ratio is governed by reactive oxygen species status. In vivo, oxalyl esters are enzymatically hydrolysed, but the carboxypentonates are stable. The biological roles of these ascorbate metabolites invite future exploration.

Review of Ireland's First Year of the COVID-19 Pandemic Impact on People Affected by Eating Disorders: 'Behind Every Screen There Was a Family Supporting a Person with an Eating Disorder'.

Irish society went into one of the most stringent lockdowns in March 2020 due to the COVID-19 pandemic, and barring a few weeks, remains highly restricted at time of writing. This has produced a wide range of challenges for those affected by eating disorders, as well as treatment services and Bodywhys, The Eating Disorders Association of Ireland. Current research indicates that COVID-19 has impacted across three key areas-the experience of those with an eating disorder, the experience of service provision, and the impact on the family situation. Drawing on monitoring and evaluation data gathered by Bodywhys, this paper details the challenges faced by those affected by eating disorders in Ireland and how the organisation responded to these challenges, providing support in various forms to people with eating disorders and their families.

Reactive oxygen species-induced release of intracellular ascorbate in plant cell-suspension cultures and evidence for pulsing of net release rate.

SUMMARY: *Apoplastic ascorbate has been proposed to confer resistance to oxidative stresses, e.g. ozone. We investigated reactive oxygen species (ROS)-induced secretion and catabolism of ascorbate. *Late-growth-phase cultured cells of rose and Arabidopsis were preloaded with [(14)C]ascorbate. Radiolabelled metabolites and secretion products were analysed by high-voltage electrophoresis. *In both species, exogenous 1 mM hydrogen peroxide (H(2)O(2)) rapidly stimulated [(14)C]ascorbate and [(14)C]dehydroascorbate accumulation in the medium (apoplast). Net (14)C export was most rapid within 100 s of washing, and often showed superimposed pulses, of c. 10-s duration, whose amplitude was greater after H(2)O(2) treatment. Oxidative stress did not cause indiscriminate metabolite leakage from the cells. H(2)O(2) caused c. 20-40% of the intracellular [(14)C]ascorbate to be irreversibly catabolized to [(14)C]oxalyl-threonate and related products; however, the great majority of the extracellular radioactivity remained as [(14)C]ascorbate and [(14)C]dehydroascorbate. Much of the apoplastic dehydroascorbate was probably reabsorbed by the cells and reduced back to ascorbate. *The data show that exported ascorbate can serve an apoplastic antioxidant role in these late-growth-phase cells without being irreversibly lost, whereas in early-growth-phase cells most extracellular ascorbate is irreversibly degraded. In conclusion, cultured plant cells can respond actively to oxidative stress by reversibly exporting ascorbate into the apoplast.

Preparation of Highly Enriched ER Membranes Using Free-Flow Electrophoresis.

Free-flow electrophoresis (FFE) is a technique for separation of proteins, peptides, organelles, and cells. With zone electrophoresis (ZE-FFE), organelles are separated according to surface charge. The ER is the only remaining major cellular compartment in Arabidopsis not to have been isolated using density centrifugation, immune-isolation, or any other method previously applied to purification of plant membranes. By using continuous-flow electrophoresis ER vesicles of similar surface charge, which may have been fragmented during cell lysis, can be focused. A large portion of these vesicles are of sufficiently different surface charge that separation from the majority of Golgi and other contaminants is possible. Here we adapt an earlier ZE-FFE Golgi isolation protocol for the isolation of highly pure ER vesicles and for tracking the migration of peripheral ER vesicles. Isolating ER vesicles of homogenous surface charge allows multi-'omic analyses to be performed on the ER. This facilitates investigations into structure-function relationships within the ER.

Ethylene Receptors, CTRs and EIN2 Target Protein Identification and Quantification Through Parallel Reaction Monitoring During Tomato Fruit Ripening.

Ethylene, the plant ripening hormone of climacteric fruit, is perceived by ethylene receptors which is the first step in the complex ethylene signal transduction pathway. Much progress has been made in elucidating the mechanism of this pathway, but there is still a lot to be done in the proteomic quantification of the main proteins involved, particularly during fruit ripening. This work focuses on the mass spectrometry based identification and quantification of the ethylene receptors (ETRs) and the downstream components of the pathway, CTR-like proteins (CTRs) and ETHYLENE INSENSITIVE 2 (EIN2). We used tomato as a model fruit to study changes in protein abundance involved in the ethylene signal transduction during fruit ripening. In order to detect and quantify these low abundant proteins located in the membrane of the endoplasmic reticulum, we developed a workflow comprising sample fractionation and MS analysis using parallel reaction monitoring. This work shows the feasibility of the identification and absolute quantification of all seven ethylene receptors, three out of four CTRs and EIN2 in four ripening stages of tomato. In parallel, gene expression was analyzed through real-time qPCR. Correlation between transcriptomic and proteomic profiles during ripening was only observed for three of the studied proteins, suggesting that the other signaling proteins are likely post-transcriptionally regulated. Based on our quantification results we were able to show that the protein levels of SlETR3 and SlETR4 increased during ripening, probably to control ethylene sensitivity. The other receptors and CTRs showed either stable levels that could sustain, or decreasing levels that could promote fruit ripening.

Enrichment of Golgi Membranes from Triticum aestivum (Wheat) Seedlings.

The Golgi apparatus is an essential component in the plant secretory pathway. The enrichment of Golgi membranes from plant tissue is fundamental to the study of this structurally complex organelle. The utilization of density centrifugation for the enrichment of Golgi membranes is still the most widely employed isolation technique. Generally, the procedure requires optimization depending on the plant tissue being employed. Here we provide a detailed enrichment procedure that has previously been used to characterize cell wall biosynthetic complexes from wheat seedlings. We also outline several downstream analyses procedures, including nucleoside diphosphatase assays, immunoblotting, and finally localization of putative Golgi proteins by fluorescent tags.

Identification and evolution of a plant cell wall specific glycoprotein glycosyl transferase, ExAD.

Extensins are plant cell wall glycoproteins that act as scaffolds for the deposition of the main wall carbohydrate polymers, which are interlocked into the supramolecular wall structure through intra- and inter-molecular iso-di-tyrosine crosslinks within the extensin backbone. In the conserved canonical extensin repeat, Ser-Hyp4, serine and the consecutive C4-hydroxyprolines (Hyps) are substituted with an α-galactose and 1-5 ß- or α-linked arabinofuranoses (Arafs), respectively. These modifications are required for correct extended structure and function of the extensin network. Here, we identified a single Arabidopsis thaliana gene, At3g57630, in clade E of the inverting Glycosyltransferase family GT47 as a candidate for the transfer of Araf to Hyp-arabinofuranotriose (Hyp-ß1,4Araf-ß1,2Araf-ß1,2Araf) side chains in an α-linkage, to yield Hyp-Araf4 which is exclusively found in extensins. T-DNA knock-out mutants of At3g57630 showed a truncated root hair phenotype, as seen for mutants of all hitherto characterized extensin glycosylation enzymes; both root hair and glycan phenotypes were restored upon reintroduction of At3g57630. At3g57630 was named Extensin Arabinose Deficient transferase, ExAD, accordingly. The occurrence of ExAD orthologs within the Viridiplantae along with its' product, Hyp-Araf4, point to ExAD being an evolutionary hallmark of terrestrial plants and charophyte green algae.

Corrigendum: Identification and evolution of a plant cell wall specific glycoprotein glycosyl transferase, ExAD.

This corrects the article DOI: 10.1038/srep45341.

'Everyone here wants everyone else to get better': The role of social identity in eating disorder recovery.

Retention of a positively valued illness identity contributes to poor outcomes for individuals with eating disorders (EDs). Consequently, dis-identification from the illness identity and the adoption of a recovery identity are vital for successful recovery. While social identity processes have been shown to influence ED maintenance, their role in recovery is rarely considered. This study explores how a sense of shared identity helps individuals with EDs manage their condition and promotes recovery. Transcripts from 18 online support sessions involving 75 participants were thematically analysed. Our findings suggest that the illness identity initially operates as a social identity that forms the basis for connections with similar others. For those wishing to recover, identity-based support is then perceived to be more effective than that found outside the group. Online interactions also facilitate construction of a new shared recovery identity which promotes a shift from the illness identity as a primary source of definition and endorses group norms of illness disclosure and treatment engagement. While in the clinical literature, ED identity is seen as problematic and interventions are targeted at challenging an individual's self-concept, we suggest that interventions could instead harness identity resources to support a transition to a recovery identity.

Beyond the Western front: targeted proteomics and organelle abundance profiling.

The application of westerns or immunoblotting techniques for assessing the composition, dynamics, and purity of protein extracts from plant material has become common practice. While the approach is reproducible, can be readily applied and is generally considered robust, the field of plant science suffers from a lack of antibody variety against plant proteins. The development of approaches that employ mass spectrometry to enable both relative and absolute quantification of many hundreds of proteins in a single sample from a single analysis provides a mechanism to overcome the expensive impediment in having to develop antibodies in plant science. We consider it an opportune moment to consider and better develop the adoption of multiple reaction monitoring (MRM)-based analyses in plant biochemistry.