Singapore grouper iridovirus(SGIV)is a major viral pathogen which can result in heavy economic losses in grouper aquaculture.SGIV is a large DNA virus containing 162 open reading frames(ORFs),among which the ORF050,a tumor necrosis factor receptor like gene,may play possible roles in the virus immune evasion.In this study,the gene of SGIV ORF050 was cloned,and the recombinant vectors containing full length gene or the four Cysteine-rich Domain(CRD)deletion mutants were constructed,respectively.RT-PCR and drug inhibition assay demonstrated that SGIV ORF050 is an immediate-early(IE)gene.Intracellular localization revealed that SIGV ORF050 is distributed in the cytoplasm evenly and gathered around the nucleus.The localization changed when the first CRD was deleted,which presented punctated distribution in the cytoplasm.The cytopathic effect(CPE)was no changed significantly in SGIV infected ORF050-expressing fish cells compared with control cells.In addition,real-time quantitative PCR(qRT-PCR)analysis showed that there was not significant change of SGIV MCP gene transcription in ORF050-expressing fish cells,suggesting that ORF050 might not have much effect on SGIV replication.Overexpressing ORF050 could enhance grouper TNF and TNFR transcription levels in SGIV infected fish cells,revealing that SGIV may regulate the host TNF/TNFR signaling pathway to evade the host immune attack via ORF050.