Abstract
Fungi, similar to all species, are susceptible to viral infection. Aspergillus is arguably the most well studied fungal genus because of its medical, ecological and economical significance. Mycoviruses were initially detected in Aspergillus species almost 50 years ago and the field continues to be active today with ground-breaking discoveries. The aim of the present review is to cover the scientific progress in all aspects of mycovirology as exemplified by Aspergillus-focused research. Initially an overview of the population studies illustrating the presence of mycoviruses in numerous important Aspergillus species, such as A. niger, A. flavus, and A. fumigatus with be presented. Moreover the intricacies of mycovirus transmission, both inter- and intra-species, will be discussed together with the methodologies used to investigate viral dispersion in a laboratory setting. Subsequently, the genomic features of all molecularly characterized mycoviruses to date will be analyzed in depth. These include members of established viral families, such as Partitiviridae, Chrysoviridae and Totiviridae, but also more recent, novel discoveries that led to the proposal of new viral families, such as Polymycoviridae, Alternaviridae and, in the context of the present review, Exartaviridae. Finally, the major issue of phenotypic effects of mycoviral infection on the host is addressed, including aflatoxin production in A. flavus, together with growth and virulence in A. fumigatus. Although the molecular mechanisms behind these phenomena are yet to be elucidated, recent studies suggest that by implication, RNA silencing may be involved.
Highlights
The diversity of known fungal viruses, or mycoviruses, has increased rapidly over the last few years and this trend is expected to continue, especially with the development and the widespread use of state-of-the-art RNA deep sequencing techniques
In the light of the above, this review aims to present the current knowledge on Aspergillus mycoviruses, from their initial identification, population and transmission studies to their phenotypes, their molecular characterisation and the discovery of novel virus families
The major established viral families, including Partitiviridae, Chrysoviridae, and Totiviridae, are well represented in Aspergillus species, while novel families such as Polymycoviridae, Alternaviridae and Exartaviridae have been proposed based on discoveries made in Aspergilli
Summary
The diversity of known fungal viruses, or mycoviruses, has increased rapidly over the last few years and this trend is expected to continue, especially with the development and the widespread use of state-of-the-art RNA deep sequencing techniques. (6) Quadriviridae (quattuor = “four” in Latin) have four genomic segments encapsidated in spherical virions and the sole genus exclusively infect fungi. (8) Endornaviridae (endos = “within” in Greek + RNA) possess nonsegmented genomes that are non-conventionally encapsidated and accommodated in host-derived lipid vesicles Both genera Alphaendoviridae and Betaendoviridae infect fungi, while the former infect plants and oomycetes. The positive-sense ssRNA mycoviruses all accommodate non-segmented genomes and are classified into five families: (1) Alphaflexiviridae genomes are encapsidated in filamentous virions and only genera Botrexvirus and Sclerodarnavirus infect fungi while the other five infect plants. The family Mymonaviridae (myco + mona) and its sole genus Sclerotimonavirus (scleroti from Sclerotinia, the host fungus, + mona) in the order Mononegavirales accommodate the only negative-sense ssRNA virus known to infect fungi, a linear molecule encapsidated in filamentous virions.
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