Concerted Action of Evolutionarily Ancient and Novel SNARE Complexes in Flowering-Plant Cytokinesis

Membrane vesicles delivered to the cell-division plane fuse with one another to form the partitioning membrane during plant cytokinesis, starting in the cell center. In Arabidopsis, this requires SNARE complexes involving the cytokinesis-specific Qa-SNARE KNOLLE. However, cytokinesis still occurs in knolle mutant embryos, suggesting contributions from KNOLLE-independent SNARE complexes. Here we show that Qa-SNARE SYP132, having counterparts in lower plants, functionally overlaps with the flowering plant-specific KNOLLE. SYP132 mutation causes cytokinesis defects, knolle syp132 double mutants consist of only one or a few multi-nucleate cells, and SYP132 has the same SNARE partners as KNOLLE. SYP132 and KNOLLE also have non-overlapping functions in secretion and in cellularization of the embryo-nourishing endosperm resulting from double fertilization unique to flowering plants. Evolutionarily ancient non-specialized SNARE complexes originating in algae were thus amended by the appearance of cytokinesis-specific SNARE complexes, meeting the high demand for membrane-fusion capacity during endosperm cellularization in angiosperms. In plant cytokinesis, SNARE complexes mediate vesicle fusion for partitioning membrane formation. Park et al. show that evolutionarily ancient Qa-SNARE SYP132 functionally overlaps with flowering plant- and cytokinesis-specific Qa-SNARE KNOLLE. KNOLLE acquisition may have been due to high demand for membrane-fusion capacity during endosperm cellularization in flowering plants

The SRG/eROSITA all-sky survey: First X-ray catalogues and data release of the western Galactic hemisphere

The eROSITA telescope array aboard the Spektrum Roentgen Gamma (SRG) satellite began surveying the sky in December 2019, with the aim of producing all-sky X-ray source lists and sky maps of an unprecedented depth. Here we present catalogues of both point-like and extended sources using the data acquired in the first six months of survey operations (eRASS1; completed June 2020) over the half sky whose proprietary data rights lie with the German eROSITA Consortium. We describe the observation process, the data analysis pipelines, and the characteristics of the X-ray sources. With nearly 930 000 entries detected in the most sensitive 0.2- 2.3 keV energy range, the eRASS1 main catalogue presented here increases the number of known X-ray sources in the published literature by more than 60%, and provides a comprehensive inventory of all classes of X-ray celestial objects, covering a wide range of physical processes. A smaller catalogue of 5466 sources detected in the less sensitive but harder 2.3- 5 keV band is the result of the first true imaging survey of the entire sky above 2 keV. We present methods to identify and flag potential spurious sources in the catalogues, which we applied for this work, and we tested and validated the astrometric accuracy via cross-comparison with other X-ray and multi-wavelength catalogues. We show that the number counts of X-ray sources in eRASSl are consistent with those derived over narrower fields by past X-ray surveys of a similar depth, and we explore the number counts variation as a function of the location in the sky. Adopting a uniform all-sky flux limit (at 50% completeness) of F05- 2 keV > 5 × 10-14 erg s-1 cm-2, we estimate that the eROSITA all-sky survey resolves into individual sources about 20% of the cosmic X-ray background in the 1- 2 keV range. The catalogues presented here form part of the first data release (DR1) of the SRG/eROSITA all-sky survey. Beyond the X-ray catalogues, DR1 contains all detected and calibrated event files, source products (light curves and spectra), and all-sky maps. Illustrative examples of these are provided

Cryofixation and Freeze-Substitution Combined with Cryosection Immunolabelling according to Tokuyasu: Improved Preservation of Ultrastructure and Antigenicity of Plant, Nematode, and Insect Tissue

Immunogold labelling on ultrathin cryosections prepared according to Tokuyasu is one of the most powerful methods for ultrastructural localization of intracellular antigens [1]. Antigens remain in an aqueous environment prior to immunolabelling and the accessibility of antigens in the thawed cryosection is better when compared to resin section labelling. The initial conventional chemical fixation step is a prerequisite in order to stabilize the ultrastructure prior to cryoprotection (sucrose infiltration), freezing, cryosectioning, thawing and immunolabelling. A severe disadvantage is that conventional chemical fixation is a relatively slow and selective process and therefore a possible source of artifacts. Here we present a hybrid technique combining the advantages of thawed cryosection labelling with the advantages of cryofixation: after cryofixation, the sample was freeze- substituted and rehydrated prior to conventional cryoprotectant infiltration, freezing, cryosectioning and labelling [2,3,4]. Immunofluorescence and immunogold labelling demonstrate the potentials of this method, especially for antigens/structures in tissues that are sensitive to aldehydes and/or cannot be fixed fast enough by conventional chemical fixation like plant tissue (ovules, anthers), nematodes and Drosophila embryos. They are well preserved after cryofixation, freeze-substitution and rehydration, even after treatment with osmium tetroxide, uranyl acetate and glutaraldehyde during freeze-substitution [4]

Endocytosis and secretion in trypanosomatid parasites - Tumultuous traffic in a pocket

Trypanosomatids are flagellated protozoan parasites of invertebrates, vertebrates and plants. Some species, found in the subtropics and tropics, cause chronic diseases in humans and domestic animals. The surface of the trypanosomatid provides a shield against environmental challenges, ligands for interaction with host cells, as well as receptors and transporters for the uptake of nutrients. Communication between the parasite and its environment is confined to the flagellar pocket, an invagination of the plasma membrane around the base of the flagellum. In this review, the authors discuss endocytosis, secretion and membrane trafficking in Trypanosoma and Leishmania