title: A novel virus-like double-stranded RNA in an obligate biotroph arbuscular mycorrhizal fungus: a hidden player in mycorrhizal symbiosis.
abstract: Arbuscular mycorrhizal (AM) fungi form mutualistic associations with most land plants and enhance phosphorus uptake of the host plants. Fungal viruses (mycoviruses) that possess a double-stranded RNA (dsRNA) genome often affect plant-fungal interactions via altering phenotypic expression of their host fungi. The present study demonstrates, for the first time, the presence of dsRNAs, which are highly likely to be mycoviruses, in AM fungi. dsRNA was extracted from mycelia of Glomus sp. strain RF1, purified, and subjected to electrophoresis. The fungus was found to harbor various dsRNA segments that differed in size. Among them, a 4.5-kbp segment was termed Glomus sp. strain RF1 virus-like medium dsRNA (GRF1V-M) and characterized in detail. The GRF1V-M genome segment was 4,557 nucleotides in length and encoded RNA-dependent RNA polymerase and a structural protein. GRF1V-M was phylogenetically distinct and could not be assigned to known genera of mycovirus. The GRF1V-M-free culture line of Glomus sp. strain RF1, which was raised by single-spore isolation, produced twofold greater number of spores and promoted plant growth more efficiently than the GRF1V-M-positive lines. These observations suggest that mycoviruses in AM fungi, at least some of them, have evolved under unique selection pressures and are a biologically active component in the symbiosis.
authors.affiliation: Graduate School of Agriculture, Hokkaido University, Sapporo, Japan.
authors.forename: Yoji
authors.initials: Y
authors.lastname: Ikeda
authors.forename: Hanako
authors.initials: H
authors.lastname: Shimura
authors.forename: Ryoko
authors.initials: R
authors.lastname: Kitahara
authors.forename: Chikara
authors.initials: C
authors.lastname: Masuta
authors.forename: Tatsuhiro
authors.initials: T
authors.lastname: Ezawa
mesh_terms: D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D001483:Base Sequence; D016679:Genome, Viral / Q000235:genetics*; D055137:Glomeromycota / Q000502:physiology / Q000821:virology*; D008969:Molecular Sequence Data; D038821:Mycorrhizae / Q000502:physiology / Q000821:virology*; D010641:Phenotype; D010802:Phylogeny; D018517:Plant Roots / Q000254:growth & development / Q000382:microbiology / Q000821:virology; D018520:Plant Shoots / Q000254:growth & development; D006109:Poaceae / Q000254:growth & development / Q000382:microbiology / Q000821:virology; D012328:RNA Viruses / Q000145:classification* / Q000235:genetics / Q000302:isolation & purification; D012330:RNA, Double-Stranded / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification*; D012367:RNA, Viral / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification; D012324:RNA-Dependent RNA Polymerase / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D016415:Sequence Alignment; D017423:Sequence Analysis, RNA; D013559:Symbiosis; D014764:Viral Proteins / Q000235:genetics
chemical_list: D012330:RNA, Double-Stranded; D012367:RNA, Viral; D014764:Viral Proteins; D012324:RNA-Dependent RNA Polymerase