Most fungal viruses are RNA viruses and no double-stranded DNA virus that infects fungi is known to date. A recent study detected DNA polymerase genes that originated from large dsDNA viruses in the genomes of basal fungi, suggestive of the existence of dsDNA viruses capable of infecting fungi. In this study, we searched for viral infection signatures in chromosome-level genome assemblies of the arbuscular mycorrhizal fungus Rhizophagus irregularis. We identified a continuous 1.5 Mb putative viral region on a chromosome in R. irregularis strain 4401. Phylogenetic analyses revealed that the viral region is related to viruses in the family Asfarviridae of the phylum Nucleocytoviricota. This viral region was absent in the genomes of four other R. irregularis strains and had fewer signals of fungal transposable elements than the other genomic regions, suggesting a recent and single insertion of a large dsDNA viral genome in the genome of this fungal strain. We also incidentally identified viral like sequences in genome assembly of the sea slug Elysia marginata that are evolutionally close to the 1.5 Mb putative viral region. In conclusion, our findings provide strong evidence of the recent infection of the fungus by a dsDNA virus.

中文翻译：

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丛枝菌根真菌不规则根噬菌中的 1.5 Mb 连续内源病毒区域

大多数真菌病毒是RNA病毒，迄今为止还没有感染真菌的双链DNA病毒。最近的一项研究在基础真菌的基因组中检测到源自大型双链DNA病毒的DNA聚合酶基因，这表明存在能够感染真菌的双链DNA病毒。在这项研究中，我们在丛枝菌根真菌不规则根噬菌的染色体水平基因组组装中寻找病毒感染特征。我们在 R.不规则菌株 4401 的染色体上发现了一个连续的 1.5 Mb 推定病毒区域。系统发育分析表明，该病毒区域与核细胞病毒门 Asfarviridae 家族的病毒有关。该病毒区域在其他四种不规则红霉菌株的基因组中不存在，并且与其他基因组区域相比，真菌转座元件的信号较少，表明最近在该真菌菌株的基因组中插入了一个大的 dsDNA 病毒基因组。我们还顺便在海蛞蝓 Elysia marginata 的基因组组装中发现了病毒样序列，这些序列在进化上接近 1.5 Mb 的假定病毒区域。总之，我们的研究结果提供了近期双链 DNA 病毒感染真菌的有力证据。