First Investigation of Grass Carp Reovirus (GCRV) Infection in Amphioxus: Insights into Pathological Effects, Transmission, and Transcriptomic Responses.

Amphioxus belongs to the subphylum Cephalochordata and occupies a transitional position in evolution between invertebrates and vertebrates. Due to the lack of viruses suitable for immunostimulation in amphioxus, this study for the first time explored the pathogenicity and waterborne transmission of Grass Carp Reovirus (GCRV), a double-stranded RNA virus, during its infection of amphioxus. Soaking amphioxus in GCRV suspension can cause obvious damage to gill tissues and severely disrupt the structure of gill filaments. The virus survived in seawater for no more than 48 h. Infection kinetics studies showed that the expression of VP5 (a viral capsid protein) mRNA in gill tissues peaked at 14 h. After co-culturing GCRV-infected amphioxus with healthy amphioxus for 72 h, the gills of healthy amphioxus showed obvious pathological damage. Additionally, the presence of the virus was verified by RT-PCR amplification of VP5 expression, indicating that GCRV can be transmitted via water. Transcriptome sequencing analysis showed that the Mitogen-Activated Protein Kinase (MAPK), calcium signaling pathway, and chitin metabolic pathway were significantly activated in amphioxus after GCRV stimulation. This study confirmed that GCRV can infect cephalochordates, revealing its gill-tropism and water-borne transmission ability, providing a new perspective for studying the cross-species infection mechanism of aquatic viruses and the prevention and control of aquatic diseases.