Rescue of synthetic salmonid rhabdovirus minigenomes

Unité de Virologie et Immunologie moléculaires, Institut National de la Recherche Agronomique, 78352 Jouy-en-Josas CEDEX, France 1 Instituto de Investigaciones Marinas, CSIC, Vigo, Spain 2 INIA, Sanidad Animal, CISA-Valdeolmos, Madrid, Spain 3 Author for correspondence: Michel Brémont. Fax +33 1 34 65 26 21. e-mail bremont{at}biotec.jouy.inra.fr Synthetic T7-driven cDNA minigenomes containing the bacterial chloramphenicol acetyltransferase gene as a reporter were derived from the genome of two salmonid novirhabdoviruses, infectious haematopoietic necrosis virus (IHNV) and viral haemorrhagic septicaemia virus (VHSV). We showed that an exogenous IHNV RNA minigenome transfected into fish cells could be rescued following IHNV infection as it was replicated, encapsidated and transcribed. When cells were infected with a recombinant vaccinia virus expressing T7 RNA polymerase (vTF7-3), transfected with the plasmid carrying the IHNV minigenome (genomic- and antigenomic-sense) and superinfected with IHNV, rescue of the minigenome was more efficient. Heterologous VHSV/IHNV rescue experiments failed. Finally, when the IHNV N, P and L proteins were expressed from cDNAs in cells, the minigenome was also successfully rescued, indicating that the nucleocapsid proteins were biologically functional. These data represent the first example of rescue experiments for non-mammalian rhabdoviruses replicating at a low temperature.