Pan, Weiqiang, Liang, Mincong, You, Yanlin, Li, Zhimin, Weng, Shaoping, He, Jianguo, and Guo, Changjun
Ranaviruses are capable of infecting both wild and farmed fish, amphibians, and reptiles, leading to significant economic losses and ecological risks. Currently, ranaviruses have been found in at least 175 species spanning six continents. Except for Singapore grouper iridovirus (SGIV), ranavirus genomes are generally regarded as highly methylated. Nevertheless, our comprehension of the methylation characteristics within ranaviruses remains limited. Despite the numerous genomes currently included in the GenBank database, a complete phylogenetic tree for ranaviruses has not yet been determined, and interspecific evolutionary relationships among ranaviruses have not been thoroughly investigated. In this study, the whole-genome methylation profile of mandarin fish ranavirus (MRV; a ranavirus) was investigated, revealing a methylation level of 16.04%, and hypomethylation of the MRV genome was detrimental to viral replication, speculating the genome methylation may play an important role in MRV replication. Furthermore, by combining with whole-genome DNA sequence phylogenetic analyses, we propose the possibility of an interspecies evolutionary relationship among ranaviruses, with the presence of four distinct evolutionary lineages within ranavirus evolution: "SGIV, SCRAV(MRV/LMBV), EHNV/ENARV/ATV, and CMTV/FV3", which might be also supported by the genomic collinearity, natural host range and host habitats. Furthermore, ranavirus genomic methylation levels may provide additional evidence for this hypothesis, but further proof is needed. Our work enhances the understanding of the role of genome methylation in ranaviruses and is beneficial for the prevention and control of ranavirus diseases; simultaneously, the proposed evolutionary hypothesis of ranavirus provides novel insights and ideas for exploring the evolutionary trajectory of viruses. Author summary: Incidents of ranavirus infections have been reported in at least 175 species of metamorphic vertebrates across six continents, including fish, amphibians, and reptiles, posing a significant threat to both wild and farmed animals and causing substantial losses to economic animal farming. Currently, the diversity and complexity of ranavirus taxonomy remain incompletely understood, and the interspecific evolutionary relationships of ranavirus have not been fully elucidated. In this study, we demonstrate that the MRV genome exhibits high levels of methylation, approximately 16.04%, which plays a pivotal role in the viral replication process. The whole-genome phylogenetic tree, genomic collinearity, natural host range, and host habitats collectively support the "SGIV, SCRAV(MRV/LMBV), EHNV/ENARV/ATV, and CMTV/FV3" hypothesis of ranavirus interspecies evolutionary relationships. Furthermore, we speculate genome methylation level may serve as evidence for the hypothesis. These findings are anticipated to provide novel insights into the taxonomic and evolutionary relationships of ranavirus and facilitate the control of the ranavirus diseases. [ABSTRACT FROM AUTHOR]