Genomic characterization of two novel viruses co-infecting the fungus Conidiobolus macrozygosporus isolate RCEF7522

Mycoviruses play diverse ecological roles ranging from conferring hypovirulence to establishing mutualistic symbioses. While these agents are vital for biocontrol, their genomic diversity within basal fungi is still poorly understood. In this study, we identified and characterized two novel double-stranded RNA (dsRNA) viruses co-infecting the basal fungus Conidiobolus macrozygosporus isolate RCEF7522. Complete genome sequences of the two viruses were determined by high-throughput sequencing and rapid amplification of cDNA ends (RACE). CmzV1 contains a dsRNA genome of 5,086 bp (G + C content: 48.3%) encoding two open reading frames (ORFs): a coat protein (CP, 852 aa, 92.46 kDa) and RNA-dependent RNA polymerase (RdRp, 731 aa, 83.18 kDa). BLASTp analysis revealed highest sequence identity with Cronartium ribicola totivirus 1 (CrTV1) at 28.61% for CP and 34.65% for RdRp. CmzV2 contains a dsRNA genome of 3,179 bp (G + C: 50.9%) encoding a hypothetical protein (HP, 285 aa, 32.98 kDa) and RdRp (672 aa, 77.19 kDa). CmzV2 shares 35.74% RdRp sequence identity with Plasmopara viticola lesion-associated virus 1 and 40-41% identity with genus Zybavirus members in the RdRp region. Phylogenetic analysis based on RdRp sequences indicates that CmzV1 clusters with genus Totivirus (family Orthototiviridae) and CmzV2 groups with genus Zybavirus (family Amalgaviridae). Based on genomic characteristics and phylogenetic relationships, CmzV1 is proposed as a novel species in genus Totivirus, and CmzV2 as a novel species in genus Zybavirus. Although the ~ 6.0 kb viral genome identified in RCEF7522 could not be fully recovered, this work expands the known diversity of mycoviruses in basal fungi and contributes to our understanding of mycovirus distribution across fungal taxa.