Molecular characterization of a new hypovirus infecting a phytopathogenic fungus, Valsa ceratosperma

Jiang

et al. 2014

J Virol

102

Botryosphaeria dothidea is an important pathogenic fungus causing fruit rot, leaf and stem ring spots and dieback, stem canker, stem death or stool mortality, and decline of pear trees. Seven double-stranded RNAs (dsRNAs; dsRNAs 1 to 7 with sizes of 3,654, 2,773, 2,597, 2,574, 1,823, 1,623, and 511 bp, respectively) were identified in an isolate of B. dothidea exhibiting attenuated growth and virulence and a sectoring phenotype. Characterization of the dsRNAs revealed that they belong to two dsRNA mycoviruses. The four largest dsRNAs (dsRNAs 1 to 4) are the genomic components of a novel member of the family Chrysoviridae (tentatively designated Botryosphaeria dothidea chrysovirus 1 [BdCV1]), a view supported by the morphology of the virions and phylogenetic analysis of the putative RNA-dependent RNA polymerases (RdRps). Two other dsRNAs (dsRNAs 5 and 6) are the genomic components of a novel member of the family Partitiviridae (tentatively designated Botryosphaeria dothidea partitivirus 1 [BdPV1]), which is placed in a clade distinct from other established partitivirus genera on the basis of the phylogenetic analysis of its RdRp. The smallest dsRNA, dsRNA7, seems to be a noncoding satellite RNA of BdPV1 on the basis of the conservation of its terminal sequences in BdPV1 genomic segments and its cosegregation with BdPV1 after horizontal transmission. This is the first report of a chrysovirus and a partitivirus infecting B. dothidea and of a chrysovirus associated with the hypovirulence of a phytopathogenic fungus. IMPORTANCEOur studies identified and characterized two novel mycoviruses, Botryosphaeria dothidea chrysovirus 1 (BdCV1) and Botryosphaeria dothidea partitivirus 1 (BdPV1), associated with the hypovirulence of an important fungus pathogenic to fruit trees. This is the first report of a chrysovirus and a partitivirus infecting B. dothidea and of a chrysovirus associated with the hypovirulence of a phytopathogenic fungus. BdCV1 appears to be a good candidate for the biological control of the serious disease induced by B. dothidea. Additionally, BdPV1 is placed in a clade distinct from the established genera. The BdCV1 capsid has two major structural proteins, and the capsid is distinct from that made up by a single polypeptide of the typical chrysoviruses. BdPV1 is the second partitivirus in which the putative capsid protein shares no significant identity with any mycovirus protein.A small accompanying dsRNA that is presumed to be a noncoding satellite RNA of BdPV1 is the first of its kind reported for a partitivirus.

Section: Methodsmentioning

confidence: 99%

Hypovirulence of the Phytopathogenic Fungus Botryosphaeria dothidea: Association with a Coinfecting Chrysovirus and a Partitivirus

Jiang

et al. 2014

J Virol

102

“…CHV1/EP713 has become the subject of the most intensive research of any filamentous fungal virus (Hillman and Suzuki, 2004;Dawe and Nuss, 2013). To date, hypoviruses have been isolated and characterized from four other phytopathogenic fungi: S. sclerotiorum (Sclerotinia sclerotiorum hypovirus 1, SsHV1) (Xie et al, 2011), Valsa ceratosperma (Valsa ceratosperma hypovirus 1, VcHV1) (Yaegashi et al, 2012), Fusarium graminearum (Fusarium graminearum hypovirus 1, FgHV1) (Wang et al, 2013), and Phomopsis longicolla (Phomopsis longicolla hypovirus 1, PlHV1) (Koloniuk et al, 2014). It is noteworthy that these four novel hypoviruses are associated with latent infections in their natural hosts.…”

Section: Introductionmentioning

confidence: 99%

“…It is noteworthy that these four novel hypoviruses are associated with latent infections in their natural hosts. Recently, Yaegashi et al (2012) proposed that the family Hypoviridae contains two lineages "Alphahypovirus" and "Betahypovirus". A phylogenetic analysis and a review of their genome features revealed that CHV3, CHV4, VcHV1, SsHV1, and PlHV1 may be assigned to "Betahypovirus" lineage, whereas CHV1, CHV2, and FgHV1 belong to the "Alphahypovirus" lineage.…”

Section: Introductionmentioning

confidence: 99%

Molecular characterization of two positive-strand RNA viruses co-infecting a hypovirulent strain of Sclerotinia sclerotiorum

Chéng

et al. 2014

Virology

Two dsRNA segments, the replicative forms of two ssRNA viruses of SsHV2/SX247 (Sclerotinia sclerotiorum hypovirus 2) and SsDRV/SX247 (Sclerotinia sclerotiorum debilitation-associated RNA virus), were isolated from the hypovirulent strain SX247 of Sclerotinia sclerotiorum. SsDRV/SX247 has the highest similarities (81% aa identity) with the previously reported virus SsDRV/Ep-1PN. The genome of SsHV2/SX247 is 15,219bp in length with a poly-A tail, and it has only one large putative open reading frame (ORF) that encodes a polyprotein containing RNA-dependent RNA polymerase (RdRp) and viral RNA helicase domains. The RdRp domain shares amino acid similarity with that of CHV1 (23%). However, the genome organization of SsHV2/SX247 is significantly different from that of CHV1 on genomic size and ORFs. We conclude that SsDRV/SX247 is a novel strain in species SsDRV of genus Sclerodarnavirus, whereas SsHV2/SX247 is a representative member of new proposed lineage Gammahypovirus in the family Hypoviridae and confers hypovirulence in its host.

“…In contrast, analysis of dsRNA patterns and virulence properties of multiple C. parasitica isolates suggested that CHV4 has little effect on fungal virulence (24). Similar analyses of dsRNA patterns and virulence properties suggested that Fusarium graminearum hypovirus 1 (FgHV1), Phomopsis longicolla hypovirus 1 (PlHV1), and Valsa ceratosperma hypovirus 1 (VcHV1) produced hypovirulence only when the fungal hosts were coinfected with separate satellite RNAs (20)(21)(22).…”

mentioning

confidence: 99%

“…Phomopsis) longicolla, Fusarium graminearum, and Valsa ceratosperma (19)(20)(21)(22). Despite what the family name implies, infection of fungal hosts by members of the Hypoviridae does not always induce hypovirulence.…”

mentioning

confidence: 99%

Transfection of Sclerotinia sclerotiorum with In Vitro Transcripts of a Naturally Occurring Interspecific Recombinant of Sclerotinia sclerotiorum Hypovirus 2 Significantly Reduces Virulence of the Fungus

Marzano

Hobbs

Nelson

et al. 2015

J Virol

A recombinant strain of Sclerotinia sclerotiorum hypovirus 2 (SsHV2) was identified from a North American Sclerotinia sclerotiorum isolate (328) from lettuce (Lactuca sativa L.) by high-throughput sequencing of total RNA. The 5=-and 3=-terminal regions of the genome were determined by rapid amplification of cDNA ends. The assembled nucleotide sequence was up to 92% identical to two recently reported SsHV2 strains but contained a deletion near its 5= terminus of more than 1.2 kb relative to the other SsHV2 strains and an insertion of 524 nucleotides (nt) that was distantly related to Valsa ceratosperma hypovirus 1. This suggests that the new isolate is a heterologous recombinant of SsHV2 with a yet-uncharacterized hypovirus. We named the new strain Sclerotinia sclerotiorum hypovirus 2 Lactuca (SsHV2L) and deposited the sequence in GenBank with accession number KF898354. Sclerotinia sclerotiorum isolate 328 was coinfected with a strain of Sclerotinia sclerotiorum endornavirus 1 and was debilitated compared to cultures of the same isolate that had been cured of virus infection by cycloheximide treatment and hyphal tipping. To determine whether SsHV2L alone could induce hypovirulence in S. sclerotiorum, a full-length cDNA of the 14,538-nt viral genome was cloned. Transcripts corresponding to the viral RNA were synthesized in vitro and transfected into a virus-free isolate of S. sclerotiorum, DK3. Isolate DK3 transfected with SsHV2L was hypovirulent on soybean and lettuce and exhibited delayed maturation of sclerotia relative to virus-free DK3, completing Koch's postulates for the association of hypovirulence with SsHV2L. IMPORTANCEA cosmopolitan fungus, Sclerotinia sclerotiorum infects more than 400 plant species and causes a plant disease known as white mold that produces significant yield losses in major crops annually. Mycoviruses have been used successfully to reduce losses caused by fungal plant pathogens, but definitive relationships between hypovirus infections and hypovirulence in S. sclerotiorum were lacking. By establishing a cause-and-effect relationship between Sclerotinia sclerotiorum hypovirus Lactuca (SsHV2L) infection and the reduction in host virulence, we showed direct evidence that hypoviruses have the potential to reduce the severity of white mold disease. In addition to intraspecific recombination, this study showed that recent interspecific recombination is an important factor shaping viral genomes. The construction of an infectious clone of SsHV2L allows future exploration of the interactions between SsHV2L and S. sclerotiorum, a widespread fungal pathogen of plants. Sclerotinia sclerotiorum (Lib.) de Bary is a cosmopolitan fungal plant pathogen that causes necrotic diseases (e.g., Sclerotinia stem rot) in more than 400 plant species, which result in yield losses in major crops each year (1-3). However, the diseases caused by S. sclerotiorum have not been adequately controlled by conventional technologies thus far (4, 5). A number of mycoviruses have been molecularly characterized and ...