The double-stranded RNA genome of maize rough dwarfFijivirus contains both mono and dicistronic segments

Abstract

An existing cDNA library of the segmented double-stranded RNA genome of maize rough dwarf virus, a plant-infecting reovirus of the genusFijivirus was used to further characterise three genome segments. Segments S7, S8 and S10 were completely sequenced and found to consist of 1936, 1900 and 1802 base pairs, respectively. They all contained the conserved structural motifs present in all genome segments of plant-infecting reoviruses. Computer analysis indicated that the coding strands of segments S7 and S10 each contained a single large open reading frame [ORF], consisting of 591 and 558 codons, respectively, as is the norm for reovirus genome segments. Segment S8 contained two large non overlapping ORFs consisting of 347 and 209 codons, located in the 5′ and 3′ terminal domains, respectively; an arrangement already described for segment S6.In vitro translation experiments confirmed that the gene products of gel-purified dsRNA genome segments S7 and S10 were single polypeptides of 68 and 63 kDa, respectively. Transcription/translation of a plasmid carrying a full-length cDNA copy of segment S8 yielded two (40 and 25 kDa) polypeptides. The nucleotide sequences of segments S7 and S10 were aligned with those of the corresponding segments of rice black-streaked dwarf virus, another member of the genusFijivirus, and found to be almost identical.