The paradigm that viruses can move directly, and in some cases covertly, between contacting target cells is now well established for several virus families. The underlying mechanisms of cell-to-cell ...spread, however, remain to be fully elucidated and may differ substantially depending on the viral exit/entry route and the cellular tropism. Here, two divergent cell-to-cell spread mechanisms are exemplified: firstly by human retroviruses, which rely upon transient adhesive structures that form between polarized immune cells termed virological synapses, and secondly by herpesviruses that depend predominantly on pre-existing stable cellular contacts, but may also form virological synapses. Plant viruses can also spread directly between contacting cells, but are obliged by the rigid host cell wall to move across pore structures termed plasmodesmata. This review will focus primarily on recent advances in our understanding of animal virus cell-to-cell spread using examples from these two virus families to highlight differences and similarities, and will conclude by comparing and contrasting the cell-to-cell spread of animal and plant viruses.
Plant RNA viruses form organized membrane-bound replication complexes to replicate their genomes. This process requires virus- and host-encoded proteins and leads to the production of double-stranded ...RNA (dsRNA) replication intermediates. Here, we describe the use of Arabidopsis thaliana expressing GFP-tagged dsRNA-binding protein (B2:GFP) to pull down dsRNA and associated proteins in planta upon infection with Tobacco rattle virus (TRV). Mass spectrometry analysis of the dsRNA-B2:GFP-bound proteins from infected plants revealed the presence of viral proteins and numerous host proteins. Among a selection of nine host candidate proteins, eight showed relocalization upon infection, and seven of these colocalized with B2-labeled TRV replication complexes. Infection of A. thaliana T-DNA mutant lines for eight such factors revealed that genetic knockout of dsRNA-BINDING PROTEIN 2 (DRB2) leads to increased TRV accumulation and DRB2 overexpression caused a decrease in the accumulation of four different plant RNA viruses, indicating that DRB2 has a potent and wide-ranging antiviral activity. We propose B2:GFP-mediated pull down of dsRNA to be a versatile method to explore virus replication complex proteomes and to discover key host virus replication factors. Given the universality of dsRNA, development of this tool holds great potential to investigate RNA viruses in other host organisms.
One manifestation of RNA silencing, known as post‐transcriptional gene silencing (PTGS) in plants and RNA interference (RNAi) in animals, is a nucleotide sequence‐specific RNA turnover mechanism with ...the outstanding property of propagating throughout the organism, most likely via movement of nucleic acids. Here, the cell‐to‐cell movement of RNA silencing in plants is investigated. We show that a short‐distance movement process, once initiated from a small group of cells, can spread over a limited and nearly constant number of cells, independent of the presence of homologous transcripts. There is also a long‐range cell‐to‐cell movement process that occurs as a relay amplification, which requires the combined activity of SDE1, a putative RNA‐dependent RNA polymerase, and SDE3, a putative RNA helicase. Extensive and limited cell‐to‐cell movements of silencing are triggered by the same molecules, occur within the same tissues and likely recruit the same plasmodesmata channels. We propose that they are in fact manifestations of the same process, and that extensive cell‐to‐cell movement of RNA silencing results from re‐iterated short‐distance signalling events. The likely nature of the nucleic acids involved is presented.
Let
be a (possibly ramified) cover, with X and Y of strictly positive genus. We develop tools to identify the Prym variety of
, up to isogeny, as the Jacobian of a quotient curve C of the Galois ...closure of a composition
of
with a well-chosen map
that identifies branch points of
. To our knowledge, this method recovers all previously obtained descriptions of Prym varieties as Jacobians. It also finds new decompositions, and for some of these, including one where X has genus 3, Y has genus 1 and
is a degree 3 map totally ramified over 2 points, we find an algebraic equation of the curve C.
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