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Porcine deltacoronavirus (PDCoV) was first identified in Hong Kong in 2012 from samples taken from pigs in 2009. PDCoV was subsequently identified in the USA in 2014 in pigs with a history of severe diarrhea. The virus has now been detected in pigs in several countries around the world. Following the development of tissue culture adapted strains of PDCoV, it is now possible to address questions regarding virus–host cell interactions for this genera of coronavirus. Here, we presented a detailed study of PDCoV-induced replication organelles. All positive-strand RNA viruses induce the rearrangement of cellular membranes during virus replication to support viral RNA synthesis, forming the replication organelle. Replication organelles for the Alpha-, Beta-, and Gammacoronavirus genera have been characterized. All coronavirus genera induced the formation of double-membrane vesicles (DMVs). In addition, Alpha- and Betacoronaviruses induce the formation of convoluted membranes, while Gammacoronaviruses induce the formation of zippered endoplasmic reticulum (ER) with tethered double-membrane spherules. However, the structures induced by Deltacoronaviruses, particularly the presence of convoluted membranes or double-membrane spherules, are unknown. Initially, the dynamics of PDCoV strain OH-FD22 replication were assessed with the onset of viral RNA synthesis, protein synthesis, and progeny particle release determined. Subsequently, virus-induced membrane rearrangements were identified in infected cells by electron microscopy. As has been observed for all other coronaviruses studied to date, PDCoV replication was found to induce the formation of double-membrane vesicles. Significantly, however, PDCoV replication was also found to induce the formation of regions of zippered endoplasmic reticulum, small associated tethered vesicles, and double-membrane spherules. These structures strongly resemble the replication organelle induced by avian Gammacoronavirus infectious bronchitis virus.

We describe how to parameterize a Poincaré section for horocycle flow on the moduli space, H(α) of translation surfaces. We give an explicit description of this Poincaré section in the case when α=2 and bound the return time under horocycle flow.

Positive-strand RNA viruses, such as coronaviruses, induce cellular membrane rearrangements during replication to form replication organelles allowing for efficient viral RNA synthesis. Infectious bronchitis virus (IBV), a pathogenic avian Gammacoronavirus of significant importance to the global poultry industry, has been shown to induce the formation of double membrane vesicles (DMVs), zippered endoplasmic reticulum (zER) and tethered vesicles, known as spherules. These membrane rearrangements are virally induced; however, it remains unclear which viral proteins are responsible. In this study, membrane rearrangements induced when expressing viral non-structural proteins (nsps) from two different strains of IBV were compared. Three non-structural transmembrane proteins, nsp3, nsp4, and nsp6, were expressed in cells singularly or in combination and the effects on cellular membranes investigated using electron microscopy and electron tomography. In contrast to previously studied coronaviruses, IBV nsp4 alone is necessary and sufficient to induce membrane pairing; however, expression of the transmembrane proteins together was not sufficient to fully recapitulate DMVs. This indicates that although nsp4 is able to singularly induce membrane pairing, further viral or host factors are required in order to fully assemble IBV replicative structures. This study highlights further differences in the mechanism of membrane rearrangements between members of the coronavirus family.

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