Complete genome sequence of a novel victorivirus infecting Aspergillus niger

The Expanding Mycovirome of Aspergilli

Mycoviruses are viruses that infect fungi and are widespread across all major fungal taxa, exhibiting great biological diversity. Since their discovery in the 1960s, researchers have observed a myriad of fungal phenotypes altered due to mycoviral infection. In this review, we examine the nuanced world of mycoviruses in the context of the medically and agriculturally important fungal genus, Aspergillus. The advent of RNA sequencing has revealed a previous underestimate of viral prevalence in fungi, in particular linear single-stranded RNA viruses, and here we outline the diverse viral families known to date that contain mycoviruses infecting Aspergillus. Furthermore, we describe these novel mycoviruses, highlighting those with peculiar genome structures, such as a split RNA dependent RNA polymerase gene. Next, we delineate notable mycovirus-mediated phenotypes in Aspergillus, in particular reporting on observations of mycoviruses that affect their fungal host's virulence and explore how this may relate to virus-mediated decreased stress tolerance. Furthermore, mycovirus effects on microbial competition and antifungal resistance are discussed. The factors that influence the manifestation of these phenotypes, such as temperature, fungal life stage, and infection with multiple viruses, among others, are also evaluated. In addition, we attempt to elucidate the molecular mechanisms that underpin these phenotypes, examining how mycoviruses can be targets, triggers, and even suppressors of RNA silencing and how this can affect fungal gene expression and phenotypes. Finally, we highlight the potential therapeutic applications of mycoviruses and how, in an approach analogous to bacteriophage therapy, their ability to produce hypovirulence in Aspergillus might be used to attenuate invasive aspergillosis infections in humans.

Co-infection of Aspergillus ochraceopetaliformis strain RCEF7483 by a novel chrysovirus and a known partitivirus

An airborne microflora isolate, Aspergillus ochraceopetaliformis RCEF7483, was found to harbor seven dsRNA elements, indicating co-infection with a novel chrysovirus and a known partitivirus. Sequence analysis and RT-PCR confirmed dsRNA5-7 as components of Aspergillus ochraceous virus (AOV), a member of the Partitiviridae family. In light of its distinct host, we have designated it Aspergillus ochraceopetaliformis partitivirus 1 (AoPV1). The dsRNA segments, named dsRNA1-4, with lengths of 3706 bp, 3410 bp, 3190 bp, and 3158 bp, respectively, constitute the genome of a novel chrysovirus designated Aspergillus ochraceopetaliformis chrysovirus 1 (AoCV1). The dsRNA1-4 segments contain five open-reading frames (ORF1-5). Specifically, ORF1 encodes a putative RNA-dependent RNA polymerase (RdRp) with a length of 1112 amino acids, and ORF2 encodes a putative coat protein (CP) spanning 976 amino acids. Additionally, ORF3-5 encode hypothetical proteins (HP1, HP2, and HP3) with lengths of 108, 843, and 914 amino acids, respectively. Comparative analysis revealed the highest similarity of dsRNA1-4 with corresponding proteins in Aspergillus terreus chrysovirus 1 (AtCV1) (RdRp, 66.58%; CP, 51.02%; HP2, 61.80%; and HP3, 41.30%). Due to falling below the threshold for a new species in the Chrysoviridae, we propose that dsRNA1-4 in A. ochraceopetaliformis strain RCEF7483 constitute the novel chrysovirus AoCV1. Moreover, phylogenetic analysis using RdRp amino acid sequences placed AoCV1 within the Alphachrysovirus genus of the Chrysoviridae family, clustering with AtCV1 and other alphachrysoviruses. Our study contributes to the understanding of mycoviruses in A. ochraceopetaliformis and expands our knowledge of the diversity and evolution of chrysoviruses in fungal hosts.