Molecular Characterization of Two Totiviruses from the Commensal Yeast Geotrichum candidum

Abstract

Mycoviruses can infect many of the major taxa of fungi including yeasts. Mycoviruses in the yeast fungus Geotrichum candidum are not well studied with only three G. candidum-associated viral species characterized to date, all of which belong to the Totiviridae genus Totivirus. In this study, we report the molecular characteristics of another two totiviruses co-infecting isolate Gc6 of G. candidum. The two totiviruses were tentatively named Geotrichum candidum totivirus 2 isolate Gc6 (GcTV2-Gc6) and Geotrichum candidum totivirus 4 isolate Gc6 (GcTV4-Gc6). Both viruses have the typical genome organization of totiviruses comprising two ORFs encoding capsid protein (CP) and RNA-dependent RNA polymerase (RdRp) at the N and C termini, respectively. The genomes of GcTV2-Gc6 and GcTV4-Gc6 are 4592 and 4530 bp long, respectively. Both viruses contain the—frameshifting elements and their proteins could be expressed as a single fusion protein. GcTV2-Gc6 is closely related to a totivirus isolated from the same host whereas GcTV4-Gc6 is related to insect-associated totiviruses. The phylogenetic analysis indicated that GcTV2-Gc6 and GcTV4-Gc6 belong to two different sister clades, I-A and I-B, respectively. It is interesting that all viruses identified from G. candidum belong to the genus Totivirus; however, this might be due to the lack of research reporting the characterization of mycoviruses from this fungal host. It is possible that the RNA interference (RNAi) mechanism cannot actively suppress totivirus accumulation in G. candidum Gc6.

Identification and Genome Characterization of a Novel Virus within the Genus Totivirus from Chinese Bayberry (Myrica rubra)

“…As discussed in a paper published in the year 2023, the presence of highly diverse microbial communities comprising fungi, bacteria, archaea, and protists colonizing plants and forming symbiotic relationships emphasizes the need for careful examination of the origin of viruses detected in viromic studies [ 22 ]. The genus Totivirus contains viruses that initially infect fungi or protozoa [ 5 , 6 , 7 ]. For a long time, viruses within the genus Totivirus were believed to only infect fungi or protozoa.…”

“…The genus Totivirus comprises viruses with a non-segmented, double-stranded RNA (dsRNA) genome, generally containing two open reading frames (ORFs) responsible for encoding the putative capsid protein (CP) and the RNA-dependent RNA polymerase (RdRP) [ 4 , 5 ]. The genus Totivirus contains viruses that initially infect fungi or protozoa [ 6 , 7 ]. However, more and more totiviruses or totivirus-like viruses have been found in a series of other eukaryotic hosts, including, but not limited to: mosquitoes [ 8 ], ants [ 9 ], fish [ 10 ], crabs [ 11 ], and plants [ 5 , 12 ].…”