Reticulon 4a facilitates grass carp reovirus replication by integrating membrane remodeling and viral protein recruitment via its reticulon homology domain.

Abstract

Grass Carp Reovirus (GCRV)-induced hemorrhagic disease imposes substantial economic losses in aquaculture, yet the molecular mechanisms by which it hijacks host factors to construct viral inclusion bodies (VIBs) remain poorly understood. This study investigates molecular mechanisms by which GCRV exploits host factors to form VIBs with a focus on grass carp Reticulon 4a (gcRTN4a). Results show that gcRTN4a, containing a conserved Reticulon homology domain (RHD), is evolutionarily convergent with vertebrate RTN4 orthologs and upregulated in immune tissues during GCRV infection. Overexpression of gcRTN4a enhances GCRV replication, viral protein expression (VP3/VP5/NS38/NS80), and VIBs formation in CIK cells. Mechanistically, GCRV induces gcRTN4a redistribution to cytoplasmic membranes, where its RHD directly interacts with viral proteins VP3/NS38, facilitating membrane bending and viral protein recruitment. ΔRHD mutants abolish membrane curvature and viral binding, confirming the dual role of RHD in VIBs biogenesis. In conclusion, this study highlights that the RHD of gcRTN4a is repurposed from its endogenous ER-shaping function to create a protective niche for GCRV replication, offering a conserved antiviral target for broad-spectrum strategies. These findings provide a paradigm for understanding host-pathogen interactions in viral replication compartment formation and offer a rationale for developing broad-spectrum antiviral strategies targeting the RHD.