Taxonomic characteristics of fijiviruses based on nucleotide sequences of the oat sterile dwarf virus genome.

Sequence determination of full-length cDNA clones of genomic segments 7-10 (S7-S10) of oat sterile dwarf fijivirus (OSDV) revealed that the 5' and 3' ends of the plus strands of these segments had the same conserved terminal sequences, 5' AACGAAAAA and UUUUUUUAGUC 3'. These sequences are similar, but not identical, to the conserved terminal nucleotide sequences of the genomic segments of rice black streaked dwarf fijivirus (RBSDV) and maize rough dwarf fijivirus (MRDV). The coding strands of S7 and S10 each contained two large nonoverlapping open reading frames (ORFs), as do RBSDV S7 and S9, MRDV S6 and S8 and Nilaparvata lugens reovirus (NLRV; a putative member of Fijivirus) S9. These results strongly suggest that the dicistronic nature of certain genomic segments is characteristic of fijiviruses. Computer analyses revealed sequence homology between RBSDV S7 ORF2, MRDV S6 ORF2 and OSDV S7 ORF2, suggesting that this protein is conserved among plant fijiviruses. No counterparts were found in the genome of NLRV, which is a nonphytopathogenic insect reovirus. Furthermore, phylogenetic trees derived from multiple sequence alignments of each of the homologous proteins from OSDV, RBSDV, MRDV and NLRV suggest that NLRV did not evolve from either Fijivirus group 2 (RBSDV and MRDV) or group 3 (OSDV).