Techniques for RNA in vivo imaging in plants

Since the discovery of small RNAs and RNA silencing, RNA biology has taken a centre stage in cell and developmental biology. Small RNAs, but also mRNAs and other types of cellular and viral RNAs are processed at specific subcellular localizations. To fully understand cellular RNA metabolism and the various processes influenced byit, techniques are required that permit the sequence-specific tracking of RNAs in living cells. A variety of methods for RNA visualization have been developed since the 1990s, but plant cells pose particular challenges and not all approaches are applicable to them. On the other hand, plant RNA metabolism is particularly diverse and RNAs are even transported between cells, so RNA imaging can potentially provide many valuable insights into plant function at the cellular and tissue level. This Short Review briefly introduces the currently available techniques for plant RNA in vivo imaging and discusses their suitability for different biological questions.PostprintPeer reviewe

Creating contacts between replication and movement at plasmodesmata – a role for membrane contact sites in plant virus infections?

Parts of this work were funded by the University of Florida, Institute of Food and Agricultural Sciences, Early Career Seed Grant No. 00127818 to AL and by the UK Biotechnology and Biomedical Sciences Research Council (BBSRC) grant BB/M007200/1 to JT.To infect their hosts and cause disease, plant viruses must replicate within cells and move throughout the plant both locally and systemically. RNA virus replication occurs on the surface of various cellular membranes, whose shape and composition become extensively modified in the process. Membrane contact sites (MCS) can mediate non-vesicular lipid-shuttling between different membranes and viruses co-opt components of these structures to make their membrane environment suitable for replication. Whereas animal viruses exit and enter cells when moving throughout their host, the rigid wall of plant cells obstructs this pathway and plant viruses therefore move between cells symplastically through plasmodesmata (PD). PD are membranous channels connecting nearly all plant cells and are now viewed to constitute a specialized type of endoplasmic reticulum (ER)-plasma membrane (PM) MCS themselves. Thus, both replication and movement of plant viruses rely on MCS. However, recent work also suggests that for some viruses, replication and movement are closely coupled at ER-PM MCS at the entrances of PD. Movement-coupled replication at PD may be distinct from the main bulk of replication and virus accumulation, which produces progeny virions for plant-to-plant transmission. Thus, MCS play a central role in plant virus infections, and may provide a link between two essential steps in the viral life cycle, replication and movement. Here, we provide an overview of plant virus-MCS interactions identified to date, and place these in the context of the connection between viral replication and cell-to-cell movement.Publisher PDFPeer reviewe

Reticulons 3 and 6 interact with viral movement proteins

Funding; This research was funded by the Science and Technology Facilities Council Programme (grant no. 14230008), a British Biotechnology and Biological Sciences Research Council (grant no. BB/J004987/1 to Professor Chris Hawes), and a Vice-Chancellors Research Fellowship to V.K. Parts of this work were funded by the U.K. Biotechnology and Biomedical Sciences Research Council (BBSRC) grant BB/M007200/1 to J.T. Work in J.T.'s laboratory is supported by the Scottish Government's Rural and Environment Science and Analytical Services Division (RESAS).Plant reticulon (RTN) proteins are capable of constricting membranes and are vital for creating and maintaining tubules in the endoplasmic reticulum (ER), making them prime candidates for the formation of the desmotubule in plasmodesmata (PD). RTN3 and RTN6 have previously been detected in an Arabidopsis PD proteome and have been shown to be present in primary PD at cytokinesis. It has been suggested that RTN proteins form protein complexes with proteins in the PD plasma membrane and desmotubule to stabilize the desmotubule constriction and regulate PD aperture. Viral movement proteins (vMPs) enable the transport of viruses through PD and can be ER-integral membrane proteins or interact with the ER. Some vMPs can themselves constrict ER membranes or localize to RTN-containing tubules; RTN proteins and vMPs could be functionally linked or potentially interact. Here we show that different vMPs are capable of interacting with RTN3 and RTN6 in a membrane yeast two-hybrid assay, coimmunoprecipitation, and Förster resonance energy transfer measured by donor excited-state fluorescence lifetime imaging microscopy. Furthermore, coexpression of the vMP CMV-3a and RTN3 results in either the vMP or the RTN changing subcellular localization and reduces the ability of CMV-3a to open PD, further indicating interactions between the two proteins.Publisher PDFPeer reviewe

Reticulons 3 and 6 interact with viral movement proteins

Plant reticulon proteins (RTN) are capable of constricting membranes and vital for creating and maintaining tubules in the endoplasmic reticulum (ER), making them prime candidates for the formation of the desmotubule in plasmodesmata (PD). RTN3 and RTN6 have previously been detected in an Arabidopsis PD proteome and have been shown to be present in primary PD at cytokinesis. It was suggested that RTN proteins form protein complexes with proteins in the PD plasma membrane and desmotubule to stabilize the desmotubule constriction and regulate PD aperture. Viral Movement Proteins (vMPs) enable the transport of viruses through PD and can be ER-integral membrane proteins or interact with the ER. Some vMPs can themselves constrict ER membranes or localise to RTN-containing tubules; RTN proteins and vMPs could be functionally linked or potentially interact. Here we show that different vMPs are capable of interacting with RTN3 and 6 in a membrane yeast-2-hybrid assay, co-immunoprecipitation and Förster resonance energy transfer measured by donor excited-state fluorescence lifetime imaging microscopy (FRET-FLIM). Furthermore, coexpression of the vMP CMV-3a and RTN3 results in either the vMP or the RTN changing subcellular localisation and reduces the ability of CMV-3a to open PD, further indicating interactions between the two proteins

Efficient detection of long dsRNA in vitro and in vivo using the dsRNA binding domain from FHV B2 protein

BM benefited from an IdEx postdoctoral fellowship from the Université de Strasbourg. Financial support to MI was provided in part by the INTERREG V Upper Rhine program Vitifutur, Transcending borders with every project. Work in the JT laboratory is funded by the U.K. Biotechnology and Biological Sciences Research Council (BB/M007200/1).Double-stranded RNA (dsRNA) plays essential functions in many biological processes, including the activation of innate immune responses and RNA interference. dsRNA also represents the genetic entity of some viruses and is a hallmark of infections by positive-sense single-stranded RNA viruses. Methods for detecting dsRNA rely essentially on immunological approaches and their use is often limited to in vitro applications, although recent developments have allowed the visualization of dsRNA in vivo. Here, we report the sensitive and rapid detection of long dsRNA both in vitro and in vivo using the dsRNA binding domain of the B2 protein from Flock house virus. In vitro, we adapted the system for the detection of dsRNA either enzymatically by northwestern blotting or by direct fluorescence labeling on fixed samples. In vivo, we produced stable transgenic Nicotiana benthamiana lines allowing the visualization of dsRNA by fluorescence microscopy. Using these techniques, we were able to discriminate healthy and positive-sense single-stranded RNA virus-infected material in plants and insect cells. In N. benthamiana, our system proved to be very potent for the spatio-temporal visualization of replicative RNA intermediates of a broad range of positive-sense RNA viruses, including high- vs. low-copy number viruses.Publisher PDFPeer reviewe

The potential consequences for cell Signaling by a class of NOD-Like Receptor proteins (NLRs) bearing an N-terminal signal sequence

The authors gratefully acknowledge the support of the UK Biotechnology and Biological Sciences Research Council (BBSRC) for the work on cellular 2A-like sequences.Publisher PDFPeer reviewe

Striking Deals : Concertation in the Reform of Continental European Welfare States

The reform of the welfare state entails changes in interdependent policy fields stretching from social policies to employment and wage policies. These linked policy fields are often governed by varying sets of corporate actors and involve different decision making procedures. Adaptation in one policy field is often uncoordinated with other policies, and can work at cross-purposes, produce negative externalities, or fail due to missing supporting conditions. The paper has two objectives. It first argues that renewed emergence of tripartite concertation is due to the need to co-ordinate policies across policy fields. Second, it evaluates the institutional factors which have facilitated concertation in some cases, but not in others. Using a similar country design, the paper compares four continental European countries with similar reform pressures but different reform trajectories: France, Germany, Italy, and the Netherlands.Die Reform des Wohlfahrtsstaates erfordert Veränderungen in interdependenten Politikfeldern, von der Sozialpolitik bis hin zur Beschäftigungs- und Lohnpolitik. Diese interdependenten Politikfelder werden von unterschiedlichen Konstellationen korporativer und politischer Akteure kontrolliert und sind unterschiedlichen Verfahren der Entscheidungsfindung unterworfen. Adaptionen in einem Sektor sind häufig nicht mit anderen politischen Entscheidungen koordiniert und können somit negative Auswirkungen haben oder aufgrund der ungünstigen Grundbedingungen fehlschlagen. In dem vorliegenden Discussion Paper wird zunächst argumentiert, daß die Notwendigkeit, politische Entscheidungen über die Grenzen der politischen Sektoren hinaus zu koordinieren, zu einer Renaissance dreiseitiger Konzertierung zwischen Tarifparteien und Regierungen geführt hat. Weiterhin werden die institutionellen Faktoren herausgearbeitet, die eine Konzertierung in einigen Fällen ermöglicht haben, in anderen jedoch nicht. Es werden vier Länder verglichen, die ähnliche Strukturen und Reformzwänge aufweisen, aber unterschiedliche Lösungswege gewählt haben: Frankreich, Deutschland, Italien und die Niederlande

F-Actin Dynamics in Neurospora crassa

This study demonstrates the utility of Lifeact for the investigation of actin dynamics in Neurospora crassa and also represents the first report of simultaneous live-cell imaging of the actin and microtubule cytoskeletons in filamentous fungi. Lifeact is a 17-amino-acid peptide derived from the nonessential Saccharomyces cerevisiae actin-binding protein Abp140p. Fused to green fluorescent protein (GFP) or red fluorescent protein (TagRFP), Lifeact allowed live-cell imaging of actin patches, cables, and rings in N. crassa without interfering with cellular functions. Actin cables and patches localized to sites of active growth during the establishment and maintenance of cell polarity in germ tubes and conidial anastomosis tubes (CATs). Recurrent phases of formation and retrograde movement of complex arrays of actin cables were observed at growing tips of germ tubes and CATs. Two populations of actin patches exhibiting slow and fast movement were distinguished, and rapid (1.2 μm/s) saltatory transport of patches along cables was observed. Actin cables accumulated and subsequently condensed into actin rings associated with septum formation. F-actin organization was markedly different in the tip regions of mature hyphae and in germ tubes. Only mature hyphae displayed a subapical collar of actin patches and a concentration of F-actin within the core of the Spitzenkörper. Coexpression of Lifeact-TagRFP and β-tubulin–GFP revealed distinct but interrelated localization patterns of F-actin and microtubules during the initiation and maintenance of tip growth

"2A-like" signal sequences mediating translational recoding : a novel form of dual protein targeting

The authors gratefully acknowledge the support of the UK Biotechnology and Biological Sciences Research Council (BBSRC) who funded this research. The authors also gratefully acknowledge the support of the Wellcome Trust for the provision of mass spectrometry facilities at St Andrews.We report the initial characterisation of an N-terminal oligopeptide ‘2A-like’ sequence that is able to function both as a signal sequence and as a translational recoding element. Due to this translational recoding activity, two forms of nascent polypeptide are synthesised: (i) when 2A-mediated translational recoding has not occurred: the nascent polypeptide is fused to the 2A-like N-terminal signal sequence and the fusion translation product is targeted to the exocytic pathway, and, (ii) a translation product where 2A-mediated translational recoding has occurred: the 2A-like signal sequence is synthesised as a separate translation product and, therefore, the nascent (downstream) polypeptide lacks the 2A-like signal sequence and is localised to the cytoplasm. This type of dual-functional signal sequence results, therefore, in the partitioning of the translation products between the two sub-cellular sites and represents a newly described form of dual protein targeting.Publisher PDFPeer reviewe

The TGB1 Movement Protein of Potato virus X Reorganizes Actin and Endomembranes into the X-Body, a Viral Replication Factory

Potato virus X (PVX) requires three virally encoded proteins, the triple gene block (TGB), for movement between cells. TGB1 is a multifunctional protein that suppresses host gene silencing and moves from cell to cell through plasmodesmata, while TGB2 and TGB3 are membrane-spanning proteins associated with endoplasmic reticulum-derived granular vesicles. Here, we show that TGB1 organizes the PVX “X-body,” a virally induced inclusion structure, by remodeling host actin and endomembranes (endoplasmic reticulum and Golgi). Within the X-body, TGB1 forms helically arranged aggregates surrounded by a reservoir of the recruited host endomembranes. The TGB2/3 proteins reside in granular vesicles within this reservoir, in the same region as nonencapsidated viral RNA, while encapsidated virions accumulate at the outer (cytoplasmic) face of the X-body, which comprises a highly organized virus “factory.” TGB1 is both necessary and sufficient to remodel host actin and endomembranes and to recruit TGB2/3 to the X-body, thus emerging as the central orchestrator of the X-body. Our results indicate that the actin/endomembrane-reorganizing properties of TGB1 function to compartmentalize the viral gene products of PVX infection