Circular single-stranded DNA (ssDNA) viruses have been rarely found in fungi, and the evolutionary and ecological relationships among ssDNA viruses infecting fungi and other organisms remain unclear. In this study, a novel circular ssDNA virus, tentatively named Diaporthe sojae circular DNA virus 1 (DsCDV1), was identified in the phytopathogenic fungus isolated from pear trees. DsCDV1 has a monopartite genome (3185 nt in size) encapsidated in isometric virions (21–26 nm in diameter). The genome comprises seven putative open reading frames encoding a discrete replicase (Rep) split by an intergenic region, a putative capsid protein (CP), several proteins of unknown function (P1–P4), and a long intergenic region. Notably, the two split parts of DsCDV1 Rep share high identities with the Reps of and , respectively, indicating an evolutionary linkage with both families. Phylogenetic analysis based on Rep or CP sequences placed DsCDV1 in a unique cluster, supporting the establishment of a new family, tentatively named , intermediate to both families. DsCDV1 significantly attenuates fungal growth and nearly erases fungal virulence when transfected into the host fungus. Remarkably, DsCDV1 can systematically infect tobacco and pear seedlings, providing broad-spectrum resistance to fungal diseases. Subcellular localization analysis revealed that DsCDV1 P3 is systematically localized in the plasmodesmata, while its expression in complementation experiments could restore systematic infection of a movement-deficient plant virus, suggesting that P3 is a movement protein. DsCDV1 exhibits unique molecular and biological traits not observed in other ssDNA viruses, serving as a link between fungal and plant ssDNA viruses and presenting an evolutionary connection between ssDNA viruses and fungi. These findings contribute to expanding our understanding of ssDNA virus diversity and evolution, offering potential biocontrol applications for managing crucial plant diseases.

中文翻译：

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环状单链 DNA 真菌病毒感染植物并赋予广谱真菌抗性


环状单链DNA（ssDNA）病毒在真菌中很少发现，感染真菌和其他生物的ssDNA病毒之间的进化和生态关系仍不清楚。在这项研究中，从梨树分离的植物病原真菌中鉴定出一种新型环状单链DNA病毒，暂命名为大豆黄豆环状DNA病毒1（DsCDV1）。 DsCDV1 具有单部分基因组（大小 3185 nt），包裹在等轴病毒体（直径 21-26 nm）中。该基因组包含七个假定的开放阅读框，编码由基因间区域、假定的衣壳蛋白（CP）、几种功能未知的蛋白质（P1-P4）和长基因间区域分开的离散复制酶（Rep）。值得注意的是，DsCDV1 Rep 的两个分裂部分分别与 和 的 Rep 具有高度同一性，表明与两个家族的进化联系。基于 Rep 或 CP 序列的系统发育分析将 DsCDV1 置于一个独特的簇中，支持建立一个新家族，暂时命名为 ，位于两个家族的中间。当转染到宿主真菌中时，DsCDV1 显着减弱真菌生长并几乎消除真菌毒力。值得注意的是，DsCDV1 可以系统地感染烟草和梨苗，从而提供对真菌病害的广谱抗性。亚细胞定位分析表明，DsCDV1 P3 系统地定位于胞间连丝，而其在互补实验中的表达可以恢复运动缺陷植物病毒的系统感染，表明 P3 是一种运动蛋白。 DsCDV1表现出其他单链DNA病毒中未观察到的独特分子和生物学特征，作为真菌和植物单链DNA病毒之间的纽带，并呈现出单链DNA病毒和真菌之间的进化联系。这些发现有助于扩大我们对单链DNA病毒多样性和进化的理解，为管理重要的植物病害提供潜在的生物防治应用。