Polycistronic (tri- or bicistronic) phytoreoviral segments translatable in both plant and insect cells

Genomic segment S12 of rice dwarf virus and segment S9 of wound tumor virus, both members of the genus Phytoreovirus, have small out-of-phase overlapping open reading frames (ORFs). Western blot (immunoblot) analysis revealed that rice dwarf virus S12 mRNA specified translation products from the large ORF and two overlapping small ORFs both in rice plant hosts and in Spodoptera frugiperda insect cells. These results provide the first example of a tricistronic mRNA for a segmented double-stranded RNA virus. Similarly, wound tumor virus S9 mRNA was found to direct the synthesis of protein products from both the large ORF and small out-of-frame ORF in S. frugiperda cells. Results of site-specific and deletion mutagenesis studies were consis-tent with a leaky scanning translation mechanism for the synthesis of the small ORFs. Rice dwarf virus (RDV) and wound tumor virus (WTV) are members of the genus Phytoreovirus (2), one of nine genera of the family Reoviridae. The properties shared by members of this genus include a double-stranded RNA genome composed of 12 independent segments and replication in both a plant host and a leafhopper insect vector. All 12 RDV segments (22) and WTV segments S4 through S12 (18) have been completel