Identification of cellular receptors used by coronavirus (CoV) entry into the host cells is critical to an understanding of pathogenesis and to development of intervention strategies. The fourth CoV genus, Deltacoronavirus , evolutionarily related to the Gammacoronavirus , has just been defined recently. In the current study, we demonstrate that porcine aminopeptidase N (pAPN) acts as a cross-genus CoV functional receptor for both enteropathogenic porcine deltacoronovirus (PDCoV) and alphacoronovirus (AlphaCoV) (transmissible gastroenteritis virus [TGEV]) based upon three lines of evidence. First, the soluble S1 protein of PDCoV bound to the surface of target porcine cell lines known to express pAPN as efficiently as TGEV-S1, which could be blocked by soluble pAPN pretreatment. Second, both PDCoV-S1 and TGEV-S1 physically recognized and interacted with pAPN by coimmunoprecipitation in pAPN cDNA-transfected cells and by dot blot hybridization assay. Finally, exogenous expression of pAPN in refractory cells conferred susceptibility to PDCoV-S1 binding and to PDCoV entry and productive infection. PDCoV-S1 appeared to have a lower pAPN-binding affinity and likely consequent lower infection efficiency in pAPN-expressing refractory cells than TGEV-S1, suggesting that there may be differences between these two viruses in the virus-binding regions in pAPN. This study paves the way for dissecting the molecular mechanisms of PDCoV-host interactions and pathogenesis as well as facilitates future vaccine development and intervention strategies against PDCoV infection. IMPORTANCE The emergence of new human and animal coronaviruses is believed to have occurred through interspecies transmission that is mainly mediated by a species-specific receptor of the host. Among the four genera of the Coronavirinae , a couple of functional receptors for the representative members in the genera Alphacoronavirus and Betacoronavirus have been identified, whereas receptors for Gammacoronavirus and Deltacoronavirus , which are believed to originate from birds, are still unknown. Porcine coronaviruses, including the newly discovered porcine deltacoronavirus (PDCoV) associated with diarrhea in newborn piglets, have posed a serious threat to the pork industry in Asia and North America. Here, we report that PDCoV employs the alphacoronavirus TGEV functional receptor porcine aminopeptidase N (pAPN) for cellular entry, demonstrating the usage of pAPN as a cross-genus CoV functional receptor. The identification of the PDCoV receptor provides another example of the expanded host range of CoV and paves the way for further investigation of PDCoV-host interaction and pathogenesis.

Porcine deltacoronavirus (PDCoV) causes severe diarrhea and vomiting in affected piglets. The aim of this study was to establish the basic, in vitro characteristics of the life cycle such as replication kinetics, cellular ultrastructure, virion morphology, and induction of autophagy of PDCoV. Time-course analysis of viral subgenomic and genomic RNA loads and infectious titers indicated that one replication cycle of PDCoV takes 5 to 6 h. Electron microscopy showed that PDCoV infection induced the membrane rearrangements with double-membrane vesicles and large virion-containing vacuoles. The convoluted membranes structures described in alpha- and beta-coronavirus were not observed. PDCoV infection also increased the number of autophagosome-like vesicles in the cytoplasm of cells, and the autophagy response was detected by LC3 I/II and p62 Western blot analysis. For the first time, this study presents the picture of the PDCoV infection cycle, which is crucial to help elucidate the molecular mechanism of deltacoronavirus replication.

Iridoviruses are an important pathogen of ectothermic vertebrates and are considered a significant threat to aquacultural fish production. Recently, one of the most economically important marine species in China, the large yellow croaker (Larimichthys crocea), has been increasingly reported to be the victim of iridovirus disease. In this study, we isolated and identified a novel iridovirus, LYCIV-ZS-2020, from cage-cultured large yellow croaker farms in Zhoushan island, China. Genome sequencing and subsequent phylogenetic analyses showed that LYCIV-ZS-2020 belongs to the genus Megalocytivirus and is closely related to the Pompano iridoviruses isolated in the Dominican Republic. LYCIV-ZS-2020 enriched from selected tissues of naturally infected large yellow croaker was used in an artificial infection trial and the results proved its pathogenicity in large yellow croaker. This is the first systematic research on the genetic and pathogenic characterization of iridovirus in large yellow croakers, which expanded our knowledge of the iridovirus.