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

Abstract

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.

50-plus years of fungal viruses

“…At least two divergent clades of "chryso-like" viruses with either 3 or up to 5 genome segments have also been described, but not yet recognized as distinct taxa by the ICTV Urayama et al, 2010Urayama et al, , 2012Wang et al, 2014). One of the viruses associated with La France disease of A. bisporus (Van der Lende et al, 1996) appears to belong to one of these clades (Urayama et al, 2012), and indeed some other of these chryso-like viruses appear to alter colony morphology and reduce virulence of their host fungi, unlike recognized chrysoviruses.…”

Short communication: Effect of mycoviruses on growth, spore germination and pathogenicity of the fungus Fusarium circinatum

“…Mycovirus infections can lead to induction of a cryptic state (asymptomatic), reduction of mycelial growth, change in the colour of the colony or even alteration of the specific structure formation (Rodríguez-García et al, 2014). The effects of mycoviruses on spore production and pathogenesis have also been widely reported (Kazmierczak et al, 1996;Wang et al, 2014, Zamora et al, 2016, indicating the potentially damaging effects of the viruses on plant health. Three different species of the genus Mitovirus that infect F. circinatum have recently been identified as putative members of Narnaviridae (genus Mitovirus) and designated Fusarium circinatum mitovirus 1, 2-1 and 2-2 (FcMV1, FcMV2-1 and FcMV2-2) (Martínez-Álvarez et al, 2014a;Vainio et al, 2015;Muñoz-Adalia et al, 2016a).…”

Analysis of an Intrinsic Mycovirus Associated With Reduced Virulence of the Human Pathogenic Fungus Aspergillus fumigatus

“…A protein with a molecular mass of 82 kDa was predicted from the 763-codon dsRNA3 ORF (ORF3; Figure 1B). A BLASTP search with the deduced amino acid sequence of ORF3 revealed that this protein had sequence homology to an 84-kDa protein encoded by PjCV1 (59% identity, 75% similarity), and to the putative capsid protein of Botryosphaeria dothidea chrysovirus (31% identity, 47% similarity) (Wang L. et al, 2014). Phylogenetic analysis of the putative AfuCV41362 capsid protein (ORF3) also suggested that AfuCV41362 belonged to Chrysoviridae cluster II ( Figure 2B and Supplementary Table S1B), as was indicated for ORF1.…”