Curvularia fungi are mostly soil and plant pathogens, which are mainly parasitic on corn, barley, oats, rice, sorghum, sugarcane and other gramineae plants, causing leaf spots, seed discoloration, seedling blight, and other symptoms [1]. Additionally, some Curvularia species may cause infections in both humans and animals, leading to diseases occurring in apparently immunocompetent hosts, e.g., mycetoma, onychomycosis, keratitis, allergic sinusitis, cerebral abscess, cerebritis, pneumonia, allergic bronchopulmonary disease, endocarditis and dialysis-associated peritonitis [2]. Therefore, Curvularia fungi are important pathogens related to both agriculture and human health. Approximately 15 years ago, a double-stranded RNA (dsRNA) virus, termed Curvularia thermal tolerance virus (CThTV), was identified in Curvularia protuberate, which has a bipartite genome comprising two dsRNA segments together with a defective dsRNA encapsidated in isometric particles [3]. CThTV is distinct from other mycoviruses in the evolution linkage, and it has not been classified into family since its RdRp sequence formed a distinct phylogenetic clade apart from other dsRNA viruses. Importantly, CThTV confers thermal tolerance to its tropical panic grass host and allows both fungus and plant to grow at high soil temperatures [3]. Considering that CThTV represents a unique specimen with a unique evolution linkage and some interesting biological traits, the mycoviral communities related to this fungal genus deserve special attention. While no more mycoviruses have been identified and characterized from this fungal community.
With the aid of high-throughput sequencing approach, the mycoviral numbers have largely increased in recent years [4–8]. Specifically, positive-sense single-stranded RNA (+ ssRNA) mycoviruses have been remarkably unveiled instead of dominant dsRNA ones in previous reports and classified into eight families, including Alphaflexi-, Gammaflexi-, Hypo-, Narna-, Barna-, Endorna-, Botourmiaviridae, and a newly proposed family "Fusariviridae" [9–12]. Of which, Mitoviridae is a noticeable family since it contains members with the simplest genome among RNA viruses, which ranges in size from 2.3–2.7 kb and encodes a single polypeptide with RNA-dependent RNA polymerase (RdRp) domains, similar to Narnaviridae, and the members replicate in the mitochondria of filamentous fungi (e.g., Sclerotinia, Alternaria, Puccinia, Rhizoctonia [10, 13, 14–19]) with genomic express relying exclusively on the mitochondrial gene (mitochondrial code), which is found in the coding region and uses UGA codon to encode tryptophan (Try). Except for some ectomycorrhizal fungi and rare plants [20], mitoviruses are mainly reported in filamentous fungi, and always impair the infected mitochondria and lead to attenuated virulence of the host fungi [15, 18, 19, 21, 22], thus as potential biocontrol agents [15, 19].
Here, a novel mitovirus, tentatively named Curvularia pseudobrachyspora mitovirus 1 (CpMV1), was detected by high-throughput sequencing approach, and its full-length was determined by Sanger sequencing RT-PCR amplification of the assembled contigs and the terminal regions by rapid amplification of cDNA ends (RACE). It represents the first report of a mitovirus infecting Curvularia fungi, and the secondary mycovirus discovered in this fungal community.