NK-611

Singapore grouper iridovirus (SGIV) belongs to the family Iridoviridae and the genus Ranavirus, which is a large cytoplasmic DNA virus. Infection of grouper with SGIV can cause hemorrhage and swelling of the spleen of the fish. Previous work on genome annotation demonstrated that SGIV contained numerous uncharacterized or hypothetical open reading frames (ORFs), whose functions remained largely unknown. In the present study, the protein encoded by SGIV ORF128 (VP128) was identified. VP128 is predominantly localized within the endoplasmic reticulum (ER). Overexpression of VP128 significantly promoted SGIV replication. VP128 inhibited the interferon (IFN)-3 promoter activity and mRNA level of IFN-related genes induced by poly(I:C), Epinephelus coioides cyclic GMP/AMP synthase (EccGAS)/stimulator of IFN genes (EcSTING), and TANK-binding kinase 1 (EcTBK1). Moreover, VP128 interacted with EcSTING and EcTBK1. The interaction between VP128 and EcSTING was independent of any specific structural domain of EcSTING. Together, our results demonstrated that SGIV VP128 negatively regulated the IFN response by inhibiting EcSTING-EcTBK1 signaling for viral evasion.

Singapore grouper iridovirus (SGIV) is a serious pathogen that negatively impacts grouper aquaculture. Because of its 90% fatality rate, effective medications that control SGIV infection are urgently needed. Glycyrrhiza uralensis is a well‐known medicinal plant that contains active ingredients with antiviral, antibacterial, and other biological activities. In this study, we evaluated the application of G. uralensis components against SGIV infection. The safe working concentrations of G. uralensis components, which were identified by light microscope observation and CCK‐8 detection, were as follows: aqueous extract (GUF) ≤ 10 mg/ml, glycyrrhizin ≤ 100 μg/ml, glycyrrhetinic acid ≤ 50 μg/ml, liquiritin ≤ 25 μg/ml, isoliquiritigenin ≤ 10 μg/ml, and liquiritigenin ≤ 10 μg/ml. The ingredients did not have significant effects against SGIV infection, whereas GUF showed significant anti‐SGIV infection activity in a concentration‐dependent manner, and it also destroyed the structure of virus particles. Therefore, GUF might impact the binding of virus particles to cell receptors and the stage of virus replication in host cells. These results show that G. uralensis aqueous extracts have good anti‐SGIV effects and great potential for treating SGIV infection.