Genomic rearrangement in genome segment 12 of rice dwarf phytoreovirus

The genome segment 12 (S12) of rice dwarf phytoreovirus (RDV) isolated from the Philippines (RDV-P) and of a variant (RDV-S-6) of RDV severe strain (RDV-S) migrated abnormally slower during polyacrylamide gel electrophoresis than that of the isolate maintained at Hokkaido University (RDV-H). Nucleotide sequence analysis revealed that rearrangement had occurred in these segments, affecting the open reading frame. A polypeptide encoded by S12 (Pns12) of RDV-P had a duplication of 28 amino acids while 1/3 of the carboxyl terminus of Pns12 was deleted in RDV-S-6 by premature termination due to a frameshift. RDV-S is always present in plants infected with the RDV-S-6 variant, suggesting that Pns12 of RDV-S-6 is defective. On the other hand, Pns12 of RDV-P was expressed and appeared to be functional in infected cells in spite of the duplication, as demonstrated by immunoblot analyses using antibody raised against Pns12 expressed in Escherichia coli.