P-266 - Novel proteins encoded by potato virus X

Although viral genomes are constrained by size, viruses excel at maximising their coding space and manipulating host cells to enable replication and spread. Recently, our lab identified new open reading frames (ORFs) in the tomato yellow leaf curl virus (TYLCV) genome that are translated into proteins during infection and are involved in the viral cycle. We thus sought to determine whether ORFs might have been missed in other viral genomes. Here, we examined the genome of potato virus X (PVX), a positive-sense single-stranded RNA virus that infects Solanaceae species, and identified 19 conserved ORFs across several PVX strains. Functional analysis of ORF knock-out mutants revealed diverse phenotypes upon infection in Nicotiana benthamiana, ranging from milder symptoms to constitutive cell death. Notably, three mutants additionally showed reduced viral loads. We confirmed the presence of the corresponding proteins for six ORFs by mass spectrometry in infected N. benthamiana leaves. Strikingly, all six ORFs reside on the negative strand, traditionally considered non-coding. We thus demonstrate that the PVX genome contains additional protein-coding genes with functional relevance. We are now investigating the function of these newly identified ORFs. Our findings suggest that we may need to revisit viral genomes to uncover overlooked genetic elements.