A Novel Totivirus Naturally Occurring in Two Different Fungal Genera

Abstract

Mycoviruses are widely distributed across different phyla of the fungal kingdom. Viruses that share significant sequence similarities have been reported in different fungi, suggesting descent from a common ancestor. In this study, two fungal genera isolated from the same sample, Trichoderma koningiopsis isolate Mg10 and Clonostachys rosea isolate Mg06, were reported to have identical double-stranded RNA (dsRNA) profiles that consist of two virus-like, dsRNA elements (dsRNA-L and dsRNA-S). The complete sequence and genome organization of dsRNA-L from isolate Mg10 was determined. It is 4712 nucleotides (nt) long and contains two non-overlapping open reading frames (ORFs) that code for proteins with similarities to totiviruses. Consequently the virus was given the proposed name Trichoderma koningiopsis totivirus 1 (TkTV1/Mg10). The TkTV1/Mg10 genome structure resembles that of yeast totiviruses in which the region preceding the stop codon of ORF1 contains the elements required for -1 ribosomal frameshifting which may induce the expression of an ORF1–ORF2 (CP-RdRp) fusion protein. Sequence analyses of viral dsRNA-L from C. rosea isolate Mg06 revealed that it is nearly identical with that of TkTV1/Mg10. This relatedness was confirmed by northern blot hybridization and indicates very recent natural horizontal transmission of this virus between unrelated fungi. TkTV1 purified isometric virions were ∼38–40 nm in diameter and were able to transfect T. koningiopsis and C. rosea protoplasts. This is another report of a mycovirus present naturally in two taxonomically distinct fungi.

Diverse Partitiviruses From the Phytopathogenic Fungus, Rosellinia necatrix

“…as well as R. necatrix that infested or colonized avocado soil of southern coastal area of Spain (Velasco et al, 2019 , 2020 ). These observations suggest that interspecific horizontal transfer of the two partitiviruses may have occurred between R. necatrix and Entoleuca sp., as previously suggested or demonstrated for different viruses (Deng et al, 2003 ; Liu et al, 2003 ; Yaegashi et al, 2013 ; Vainio and Hantula, 2016 ; Khalifa and MacDiarmid, 2019 ). The coinfection of two fungal hosts by the same set of two taxonomically different partitiviruses (alpha- and betapartitiviruses) suggests the possibility of mutualistic or commensal interactions between the coinfecting partitiviruses.…”

A Novel Virus Discovered in the Yeast Pichia membranifaciens

“…P. membranifaciens has potentially hosted totiviruses that are more closely related to viruses found within Saccharomyces yeasts as evinced by genome integrated viral sequences in P. membranifaciens [45]. This would suggest the possibility of horizontal transmission of viral dsRNAs between yeasts as has also been shown by phylogenic analysis of mycoviruses and satellite dsRNAs from different yeast species [13,45,46].…”

Characterization of Four Novel dsRNA Viruses Isolated from Mucor hiemalis Strains

“…It is worth mentioning that Trichoderma koningiopsis is a known mycoparasite. Furthermore, Khalifa and MacDiarmid recently detected TkTV1 in a T. koningiopsis strain isolated from a sample, which also contained a Clonostachys rosea strain [34]. The latter fungus harbored a virus, of which the genome proved to be nearly identical with that of TkTV1, suggesting the possibility of a natural horizontal transmission event.…”