Type II grass carp reovirus utilizes autophagosomes for viroplasm formation and subclinical persistent infection.

Abstract

Grass carp reovirus (GCRV) is the most virulent pathogen within the genus Aquareovirus, belonging to the family Spinareoviridae. GCRV is categorized into three genotypes, with type II (GCRV-II) being the predominant strain circulating in China. Reoviruses are known to replicate and assemble in cytoplasmic inclusion bodies termed viroplasms; however, information regarding the formation of GCRV-II viroplasms and their specific roles in virus infection remains largely unknown. In this study, we investigated the formation and characteristics of viroplasms during GCRV-II infection. Immunofluorescence and confocal microscopy indicate that GCRV-II infection induces the formation of viroplasms, with the nonstructural protein NS79 being the key protein responsible for this process. Live-cell imaging and fluorescence recovery after photobleaching assays reveal that GCRV-II viroplasms lack liquid-like properties. Transmission electron microscopy confirms that GCRV-II viroplasms are membranous structures. Notably, we demonstrate that GCRV-II infection induces autophagy and the formation of autophagosomes and that GCRV-II utilizes these autophagosomes for viroplasm formation and virion assembly. Furthermore, we found that GCRV-II uses autophagosomes to evade the host immune system, establishing subclinical persistent infection. GCRV-II also employs autophagosomes for nonlytic release and viral spread. Collectively, these findings highlight distinctive characteristics of GCRV-II viroplasms compared to those of other animal reoviruses, offering valuable insights for the prevention and control of this virus.IMPORTANCEGrass carp reovirus (GCRV) is categorized into three genotypes, with GCRV-II being the most prevalent in China. Despite reoviruses being known for their replication and assembly in viroplasms, the specifics of GCRV-II viroplasm formation and its role in infection were unclear. Our study demonstrates that GCRV-II infection triggers the formation of viroplasms, primarily mediated by the nonstructural protein NS79. GCRV-II viroplasms are membranous structures that lack liquid-like properties, which are significantly different from the viroplasms of other reoviruses. Notably, our research unveils that GCRV-II infection induces autophagy and utilizes autophagosomes for viroplasm formation and virion assembly. Furthermore, we also confirm that GCRV-II utilizes autophagosomes for subclinical persistent infection, nonlytic release, and viral spread. Our results indicate that GCRV-II hijacks autophagosomes to form viroplasms and complete its life cycle. The characteristics of GCRV-II are significantly different from those of other animal reoviruses, providing important information for prevention and control of this virus.