A novel betapartitivirus RnPV6 from Rosellinia necatrix tolerates host RNA silencing but is interfered by its defective RNAs

• Published in: Virus research 2016-07, Vol.219, p.62-72
• Main Authors: Chiba, Sotaro, Lin, Yu-Hsin, Kondo, Hideki, Kanematsu, Satoko, Suzuki, Nobuhiro
• Format: Article
• Language: English
• Subjects: Ascomycota - genetics; Ascomycota - virology; Base Sequence; Cryphonectria parasitica; Defective RNA; dsRNA virus; Fungal Viruses - genetics; Gene Expression Regulation, Viral; Gene Silencing; Genome, Viral; Partitiviridae; Partitivirus; Phylogeny; RNA Interference; RNA silencing; RNA, Fungal - genetics; RNA, Viral - genetics; Rosellinia necatrix; Transcription, Genetic
• ISSN: 0168-1702; 1872-7492
• DOI: 10.1016/j.virusres.2015.10.017

•A novel betapartitivirus from Rosellinia necatrix (RnPV6) was characterized.•RnPV6 showed asymptomatic infection in the natural host.•RnPV6 induced severe symptoms in an experimental host, Cryphonectria parasitica.•Diverse dsRNA1-derived DI-RNAs were generated in C. parasitica.•DI-RNAs impaired RnPV6 replication, while RnPV6 tolerated host RNA silencing. The family Partitiviridae comprises of five genera with bi-segmented dsRNA genomes that accommodate members infecting plants, fungi or protists. All partitiviruses with only a few exceptions cause asymptomatic infections. We report the characterization of a novel betapartitivirus termed Rosellinia necatrix partitivirus 6 (RnPV6) from a field isolate of a plant pathogenic fungus, white root rot fungus. RnPV6 has typical partitivirus features: dsRNA1 and dsRNA2 are 2462 and 2499bps in length encoding RNA-dependent RNA polymerase and capsid protein. Purified particles are spherical with a diameter of 30nm. Taking advantage of infectivity as virions, RnPV6 was introduced into a model filamentous fungal host, chestnut blight fungus to investigate virus/host interactions. Unlike other partitiviruses tested previously, RnPV6 induced profound phenotypic alterations with symptoms characterized by a reduced growth rate and enhanced pigmentation and was tolerant to host RNA silencing. In addition, a variety of defective RNAs derived from dsRNA1 appear after virion transfection. These sub-viral RNAs were shown to interfere with RnPV6 replication, at least for that of cognate segment dsRNA1. Presence of these sub-viral elements resulted in reduced symptom expression by RnPV6, suggesting their nature as defective-interfering RNAs. The features of RnPV6 are similar to but distinct from those of a previously reported alphapartitivirus, Rosellinia necatrix partitivirus 2 that is susceptible to RNA silencing.