Transcriptome analysis of African swine fever virus I9R-mediated modulation of host antiviral immunity

African swine fever (ASF) is an acute hemorrhagic disease caused by African swine fever virus (ASFV), with mortality rates approaching 100% in domestic pigs. Because its genome is large and structurally complex, the functions of many ASFV encoded genes remain poorly understood. In this study, ASFV I9R was identified as a relatively conserved early transcribed gene. To investigate its biological role, an I9R deletion recombinant virus (ASFV-ΔI9R) was generated by replacing the I9R gene with an enhanced green fluorescent protein (EGFP) expression cassette. In primary porcine alveolar macrophages (PAMs), ASFV-ΔI9R and the parental ASFV CN/GS/2018-WT (ASFV-WT) exhibited identical replication kinetics, indicating that I9R is dispensable for viral replication in vitro. Transcriptome sequencing (RNA-seq) analysis of infected PAMs at 18 and 36 hour post infection (hpi) showed that differentially expressed genes (DEGs) in ASFV-ΔI9R-infected cells were mainly enriched in innate immune signaling pathways, particularly pathways associated with type I interferon (IFN-β) mediated antiviral responses. Further analyses demonstrated that ASFV-ΔI9R infection reduced IFN-β-induced the expression of interferon-stimulated gene 12A (ISG12A) and inhibited phosphorylation levels of STAT1 and STAT2, key components of the JAK-STAT signaling pathway. Collectively, these findings suggest that I9R is involved in modulation of host antiviral responses through the JAK-STAT signaling pathway. This study provides additional insights into ASFV host interactions and contributes to understanding the biological functions of ASFV encoded genes.