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.
Highlights
Mycoviruses, viruses that infect fungi, are widely distributed and have been reported in several fungal groups (Pearson et al, 2009)
The genome consists of two overlapping open reading frames (ORFs) coding for a coat protein (CP or Gag) and an RNA-dependent RNA polymerase (RdRp or Pol) that could be expressed as a gag-pol fusion protein (Dinman et al, 1991; Ghabrial, 2008)
Characterized double-stranded RNA (dsRNA) have been previously reported in two isolates of T. koningiopsis (Yun et al, 2016) and nothing is yet known about the association of C. rosea with mycoviruses
Summary
Reviewed by: Jie Zhong, Hunan Agricultural University, China Mingde Wu, Huazhong Agricultural University, China. 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. 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
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