Fungi are generally thought to live in host plants with a single lifestyle, being parasitism, commensalism, or mutualism. The former, known as phytopathogenic fungi, cause various plant diseases that result in significant losses every year; while the latter, such as endophytic fungi, can confer fitness to the host plants. It is unclear whether biological factors can modulate the parasitic and mutualistic traits of a fungus. In this study, we isolated and characterized a mycovirus from an endophytic strain of the fungus Pestalotiopsis theae, a pathogen of tea (Camellia sinensis). Based on molecular analysis, we tentatively designated the mycovirus as Pestalotiopsis theae chrysovirus-1 (PtCV1), a novel member of the family Chrysoviridae, genus Alphachrysovirus. PtCV1 has four double-stranded (ds) RNAs as its genome, ranging from 0.9 to 3.4 kbp in size, encapsidated in isometric particles. PtCV1 significantly reduced the growth rates of its host fungus in vitro (ANOVA; P-value < 0.001) and abolished its virulence in planta (ANOVA; P-value < 0.001), converting its host fungus to a non-pathogenic endophyte on tea leaves, while PtCV1-free isolates were highly virulent. Moreover, the presence of PtCV1 conferred high resistance to the host plants against the virulent P. theae strains. Here we report a mycovirus that modulates endophytic and phytopathogenic fungal traits and provides an alternative approach to biological control of plant diseases caused by fungi.

真菌通常被认为以单一的生活方式生活在寄主植物中，即寄生、共生或共生。前者被称为植物病原真菌，会引起各种植物病害，每年造成重大损失；而后者，如内生真菌，可以赋予寄主植物适应性。目前尚不清楚生物因素是否可以调节真菌的寄生和共生特性。在这项研究中，我们从茶叶病原体Pestalotiopsis theae的内生菌株中分离并鉴定了一种真菌病毒。基于分子分析，我们暂时将这种真菌病毒命名为 Pestalotiopsis theae chrysovirus-1 (PtCV1)，它是 Chrysoviridae 属的一个新成员Alphachrysovirus。PtCV1 有四个双链 (ds) RNA 作为其基因组，大小范围为 0.9 至 3.4 kbp，包裹在等距颗粒中。PtCV1 在体外显着降低其宿主真菌的生长速率（方差分析；P值 < 0.001）并消除其在植物中的毒力（方差分析；P值 < 0.001），将其宿主真菌转化为茶叶上的非致病性内生菌，而无 PtCV1 的分离株毒性很强。此外，PtCV1 的存在赋予宿主植物对强毒P. theae菌株的高抗性。在这里，我们报告了一种调节内生和植物病原真菌性状的真菌病毒，并为真菌引起的植物病害的生物防治提供了一种替代方法。