Molecular Characterization of a Debilitation-Associated Partitivirus Infecting the Pathogenic Fungus Aspergillus flavus

Abstract

The opportunistic human pathogenic fungus Aspergillus flavus is known to be infected with mycoviruses. In this study, we report a novel mycovirus A. flavus partitivirus 1 (AfPV1) that was originally isolated from the abnormal colonial morphology isolate LD-3-8 of A. flavus . AfPV1 has spherical virus-like particles about 40 nm in diameter, and three double-stranded RNA (dsRNA) segments (dsRNA1, 2, and 3 with lengths of 1.7, 1.4, and 1.1 kbp, respectively) were packaged in the virions. dsRNA1, dsRNA2, and dsRNA3 each contained a single open reading frame and potentially encoded 62, 42, and 32 kDa proteins, respectively. The dsRNA1 encoded protein shows similarity to the RNA-dependent RNA polymerase (RdRp) of partitiviruses, and the dsRNA2 product has no significant similarity to any other capsid protein (CP) in the GenBank databases, beside some homology with the hypothetical “capsid” protein of a few partitiviruses. The dsRNA3 encodes a protein with no similarity to any protein in the GenBank database. SDS-PAGE and polypeptide mass fingerprint-mass spectrum (PMF-MS) analyses indicated that the CP of the AfPV1 was encoded by dsRNA2. Phylogenetic analysis showed that the AfPV1 and relative viruses were found in an unclassified group inside the Partitiviridae family. AfPV1 seems to result in debilitation symptoms, but had no significant effects to murine pathogenicity. These findings provide new insights into the partitiviruses taxonomy and the interactions between viruses and A. flavus .

Completion of the sequence of the Aspergillus fumigatus partitivirus 1 genome

“…1d). This is consistent with observations for multi-component RNA viruses, where the 5'-terminal sequences are essential for recognition by the viral RdRP during viral RNA replication [6]. Such conserved sequences proximal to the 5'termini of partitiviruses are thought to be involved in RdRP recognition for RNA packaging and/or replication [17].…”

“…On occasion, smaller dsRNAs than the two dsRNAs described above encoding proteins of unknown function have been reported for some partitiviruses. Examples include Ustilaginoidea virens partitivirus 1 (UvPV-1) [18], Gremmeniella abietina RNA viruses MS1, MS2 and MS3 (GaRV-MS1, -MS2 and -MS3) [3,15,16], Aspergillus ochraceous virus (AoV) [10,11] and Aspergillus flavus partitivirus 1 (AfPV-1) [6], but not Aspergillus fumigatus partitivirus 1 (AfuPV-1) [2] or a second isolate of UvPV [7]. During our continued monitoring of the incidence of mycoviruses in Aspergillus fumigatus, an opportunistic pathogen causing aspergillosis in the immunocompromised human population, we isolated, cloned and sequenced a Portuguese strain of AfuPV-1 termed AfuPV-1A.…”

Diverse Partitiviruses From the Phytopathogenic Fungus, Rosellinia necatrix

“…Cryspoviruses have been isolated from protozoa of the genus Cryptosporidium that infect mammals as a parasite. Recently, the novel genera “ Epsilonpartitivirus ” and “ Zetapartitivirus ” have been proposed for some novel viruses or virus-like agents associated with fungi and arthropods (Nerva et al, 2017a ; Jiang et al, 2019 ). Partitiviruses, in most cases, produce symptomless infections.…”

“…Partitiviruses, in most cases, produce symptomless infections. Exceptions include growth-reducing Heterobasidion partitivirus 3 (an alphapartitivirus) (Vainio et al, 2010 ) and Aspergillus fumigatus partitivirus 1 (a gammapartitivirus) (Bhatti et al, 2011 ), and hypovirulence-conferring partitiviruses such as Rhizoctonia solani partitivirus 2 (an alphapartitivirus, RsPV2) (Zheng et al, 2014 ), Sclerotinia sclerotiorum partitivirus 1 (a betapartitivirus, SsPV1) (Xiao et al, 2014 ), Aspergillus flavus partitivirus 1 (a zetapartitivirus) (Jiang et al, 2019 ) and Heterobasidion partitivirus 13 (an alphapartitivirus) (Vainio et al, 2018b ). In other cases, some partitiviruses have been shown to contribute to hypovirulence and/or growth defects induced by other co-infecting fungal dsRNA viruses such as megabirnavirus and chrysovirus (Wang et al, 2014 ; Sasaki et al, 2016 ).…”

A Novel Partitivirus That Confer Hypovirulence to the Plant Pathogenic Fungus Colletotrichum liriopes

“…Phylogenetic analysis using the aa sequences of RdRp and CP indicated that ClPV1 was clustered with members of the putative genus Epsilonpartitivirus in the family Partitiviridae. Thus, according to genome organization, viral particle morphology, complete nucleotide sequences, and Members of the family Partitiviridae are generally considered latent on their hosts (Ghabrial et al, 2015), even though some of them cause morphological alterations (Magae and Sunagawa, 2010;Bhatti et al, 2011;Jiang et al, 2019), hypovirulence (Potgieter et al, 2013;Xie and Jiang, 2014;Zheng et al, 2014), or hypervirulence (Lau et al, 2018). To our knowledge, there have been no reports of hypovirulence caused by a partitivirus or even mycovirus infection in the pathogenic fungus C. liriopes.…”