Population Structure of Double-Stranded RNA Mycoviruses That Infect the Rice Blast Fungus Magnaporthe oryzae in Japan

Abstract

Various viruses infect Magnaporthe oryzae (syn. Pyricularia oryzae), which is a well-studied fungus that causes rice blast disease. Most research has focused on the discovery of new viruses and the hypovirulence-associated traits conferred by them. Therefore, the diversity and prevalence of viruses in wild fungal populations have not been explored. We conducted a comprehensive screening of M. oryzae mycoviruses from various regions in Japan using double-stranded RNA (dsRNA) electrophoresis and RT-PCR assays. We detected three mycoviruses, Magnaporthe oryzae virus 2 (MoV2), Magnaporthe oryzae chrysovirus 1 (MoCV1), and Magnaporthe oryzae partitivirus 1 (MoPV1), among 127 of the 194 M. oryzae strains screened. The most prevalent virus was MoPV1 (58.8%), which often co-infected in a single fungal strain together with MoV2 or MoCV1. MoV2 and MoCV1 were found in 22.7 and 10.8% of strains, respectively, and they were usually distributed in different regions so that mixed-infection with these two mycoviruses was extremely rare. The predominance of MoPV1 in M. oryzae is supported by significant negative values from neutrality tests, which indicate that the population size of MoPV1 tends to increase. Population genetic analyses revealed high nucleotide diversity and the presence of phylogenetically diverse subpopulations among the MoV2 isolates. This was not the case for MoPV1. Furthermore, studies of a virus-cured M. oryzae strain revealed that MoV2 does not cause any abnormalities or symptoms in its host. However, a leaf sheath inoculation assay showed that its presence slightly increased the speed of mycelial growth, compared with virus-free mycelia. These results demonstrate that M. oryzae in Japan harbors diverse dsRNA mycovirus communities with wide variations in their population structures among different viruses.

Six Novel Mycoviruses Containing Positive Single-Stranded RNA and Double-Stranded RNA Genomes Co-Infect a Single Strain of the Rhizoctonia solani AG-3 PT

“…Metatranscriptome sequencing can also alter the diagnosis of a singular infection in fungi to a cryptic co-infection [6,9]. In fact, metatranscriptome sequencing has revealed diverse mycoviruses co-infecting a single isolate of a fungal host and demonstrated that this is a common occurrence [2,[10][11][12][13][14].…”

“…Since the first mycovirus was detected in R. solani in 1978 [27], more than 100 mycoviruses have been identified in this pathogenic fungus [28][29][30][31][32]. To date, the mycoviruses identified in R. solani are double-stranded RNA (dsRNA), positive single-stranded RNA (+ssRNA), or negative single-stranded RNA (−ssRNA) viruses, and include members of established families as well as members of proposed families and unclassified RNA viruses [11], such as Rhizoctonia solani virus 717 (dsRNA, Partitiviridae) [33], Rhizoctonia solani parititivirus 2 (dsRNA, Partitiviridae) [34], Rhizoctonia solani fusarivirus 1 (+ssRNA, proposed family Fusariviridae) [35], Rhizoctonia solani mitovirus 39 (+ssRNA, Mitoviridae) [36], Rhizoctonia solani negative-stranded virus 1 (−ssRNA, proposed family Betamycoserpentoviridae) [12], Rhizoctonia solani mycovirus 2 (dsRNA, proposed family Bipartitiviridae), etc. [37].…”

Characterization of the Mycovirome of the Phytopathogenic Fungus, Neofusicoccum parvum

“…Co-infections of mycoviruses are common in plant pathogenic fungi, and the determinants of the assembly rules of the mycovirome are not properly understood but are thought to involve multiple factors such as non-self-recognition, RNA silencing, or a role of nutrients or environmental constraints [48,49]. The biology of the co-infections is still very difficult to study and could be very complex, depending on the fungal host, the nature of the mycoviruses, and the interactions between the co-infecting viruses themselves, ranging from synergism to neutrality, antagonism, or mutualism [50].…”

Incidence of putative RNA mycoviruses in entomopathogenic fungi in Korea

“…Mycoviruses are a group of viruses that infect fungi, whose genomes usually consist of double-stranded (ds) RNA (e.g., families Chrysoviridae, Partitiviridae, Polymycoviridae, and Totiviridae), or single-stranded (ss) RNA (e.g., family Hadakaviridae) [1,22]. Among them, viruses with dsRNA genomes account for the majority of known mycoviruses and are the most studied [19]. Most mycovirus infections are cryptic and have no discernible symptoms.…”