Recently, a research paper titled “A tripartite ssDNA mycovirus from a plant pathogenic fungus is infectious as cloned DNA and purified virions”, was published in the journal Science Advances by Prof. Guo Lihua and co-workers at IPP-CAAS. In this report, the authors presented FgGMTV1 as the first multipartite DNA virus isolated from a fungus. Phylogenetic analyses also suggested that the multipartite genome of FgGMTV1 may have evolved from a monopartite genome of an ancient genomovirus. They also constructed the first infectious DNA clones of a DNA mycovirus and analyzed the biological function of FgGMTV1.
Recently, a research paper titled “A tripartite ssDNA mycovirus from a plant pathogenic fungus is infectious as cloned DNA and purified virions”, was published in the journal Science Advances by Prof. Guo Lihua and co-workers at IPP-CAAS. In this report, the authors presented FgGMTV1 as the first multipartite DNA virus isolated from a fungus. Phylogenetic analyses also suggested that the multipartite genome of FgGMTV1 may have evolved from a monopartite genome of an ancient genomovirus. They also constructed the first infectious DNA clones of a DNA mycovirus and analyzed the biological function of FgGMTV1.
To date, multiparticulate fungal viruses or mycoviruses have been classified into four families and one genus with linear dsRNA virus genomes (Chrysoviridae, Megabirnaviridae, Partitiviridae, Quadriviridae, and Botybirnavirus). In addition, no mycoviruses with multipartite DNA genomes have previously been reported. FgGMTV1 is the first multipartite DNA virus infecting fungi. Previous to this work, only infectious cDNA clones of RNA mycoviruses have been constructed. Our knowledge of circular replication-associated protein-encoding single-stranded (CRESS) DNA virus diversity has significantly increased in recent years due to innovations in molecular techniques and sequencing technologies. CRESS DNA viruses have been identified in environmental, fungal, plant, and animal samples. Because of the huge diversity, variable genome organizations, and unknown hosts, a large number of recently identified CRESS DNA viruses cannot be classified into any known viral families, which has resulted in large, novel CRESS DNA viral groups being proposed. One of the recently proposed groups is the family Genomoviridae. Currently, there are nine approved genera in this family: Gemycircularvirus, Gemyduguivirus, Gemygorvirus, Gemykibivirus, Gemykolovirus, Gemykrogvirus, Gemykroznavirus, Gemytondvirus, and Gemyvongvirus. These viruses have small (~2 to 2.4 kb), circular ssDNA genomes, and they encode rolling-circle replication initiation proteins (Rep) that are mostly similar to those of geminiviruses, as well as unique capsid proteins.
In this study, a tripartite ssDNA mycovirus (FgGMTV1) from a plant pathogenic fungus, Fusarium graminearum, was identified. The genome of FgGMTV1 comprises three circular ssDNA components of ~1.3 kb in size referred to as DNA-A (encoding the replication protein), DNA-B (encoding the capsid protein), and DNA-C (encoding an unknown protein), respectively. The evidence suggested that the mycovirus FgGMTV1 is a representative member of the newly proposed genus Gemytripvirus in the family Genomoviridae. The authors successfully constructed infectious clone vectors of these three DNA components and used them to identify essential and symptom-associated components, providing a good system for the study of virus-fungus interactions. Results showed that DNA-A and DNA-B are mutually interdependent for their replication and are associated with severely reduced colony growth and hypovirulence. DNA-C relies on DNA-A and DNA-B for replication and is necessary for the recovery of abnormal fungal phenotypes. DNA-C also enhances the accumulation of viral DNA in infected fungi and permits stable colonization and easy transmission via conidia. These clones will allow future further exploration of the interaction between FgGMTV1 and F. graminearum and could be also applicable to effectively extend the infection of FgGMTV1 to other hosts and enable manipulation of FgGMTV1 for both fundamental and practical applications.
