The role of ORF3 accessory protein in replication of cell-adapted porcine epidemic diarrhea virus (PEDV)

The ORF3 accessory protein has been shown to impede reverse genetics of cell-culture-adapted porcine epidemic diarrhea virus (PEDV). Its absence or truncated variants are also associated with viral attenuation in vivo. Here, three ORF3 variants (ORF3_NP12, ORF3_NP14 and ORF3_RB14) and their truncated counterparts were investigated for their regulatory role in recovery of cell-adapted PEDV in vitro. We demonstrate that ORF3_NP12, but not the truncated form, can inhibit recovery of reverse-genetics-derived PEDV when expressed in trans. When testing with other RNA viruses, ORF3 was found to inhibit rescue of porcine respiratory and reproductive syndrome virus (PRRSV), but not of influenza virus. Interestingly, results from mutagenesis of ORF3_NP12 suggest that F81 and M167 are responsible for impairing PEDV rescue in vitro. By changing specific residues of ORF3, the recombinant PEDV bearing the modified ORF3_NP12 can be productively propagated in VeroE6-APN cells. These results may provide mechanistic insights into ORF3-mediated inhibition of PEDV replication in new host cells.