Marek’s disease virus-encoded MicroRNA-M6-5p suppresses viral replication by targeting viral major capsid protein-coding gene UL19

Marek’s disease virus (MDV) is a cell-associated alphaherpesvirus that causes lymphoproliferative diseases in chickens. MicroRNAs (miRNAs) are a class of 20–25-nucleotide long single-stranded non-coding RNAs that play an important role in post-transcriptional regulation. MDV-encoded miRNAs are critical for viral replication and tumorigenesis; however, the underlying mechanisms remain unclear. We have previously found that MDV-encoded miR-M6-5p inhibits viral replication in vitro. In this study, we identified the major viral capsid protein-coding gene UL19 as a direct functional target of miR-M6-5p. The overexpression of miR-M6-5p significantly reduced UL19 expression, accompanied by a decrease in the number of viral particles. In contrast, the knockout of miR-M6-5p enhanced UL19 expression, accompanied by an increase in the number of viral particles. Consistently, MDV mutants with UL19 deletions could not replicate and assemble capsid structures in infected cells. Thus, miR-M6-5p inhibits MDV replication by impairing capsid assembly by targeting the UL19 gene. These findings reveal how virus-encoded miRNAs regulate viral replication by targeting structural morphogenic components and broaden our understanding of the role of MDV-encoded miRNAs in viral replication.