Mycovirome of Diaporthe helianthi and D. gulyae, causal agents of Phomopsis stem canker of sunflower

Diaporthe helianthi and D. gulyae cause Phomopsis stem canker, which is a yield-limiting fungal disease of sunflower (Helianthus annuus L.) in the United States. In this study the mycovirus was characterized in D. gulyae and D. helianthi using 52 and 42 isolates respectively that were recovered from diseased sunflower plants randomly sampled from commercial fields in the U.S. states of Minnesota, Nebraska, North Dakota, and South Dakota. Total RNA extracts depleted of rRNA from each fungus were pooled to construct one library for sequencing to obtain 20GB per library of raw reads using a metatranscriptomics approach. Between the two libraries, they only share one mycovirus in a high amount. Twenty-one novel viral contigs and 10 viral contigs were discovered infecting D. gulyae and D. helianthi, respectively, along with a plant virus contig that was detected as Cucumber green mosaic virus coat protein, indicating trans-kingdom transmission of the same viruses. Among the viruses infecting D. helianthi, we detected two of the same viruses, Helianthus annus leaf-associated partitivirus 3 and 5, that were detected in a direct sunflower virome reported before. Interestingly, Qinvirus which is mostly known as a group of insect viruses, was found in a contig. There was also a circular ssDNA virus contig detected in the D. gulyae library aside from ss (+)RNA, ss (-)RNA, and dsRNA viruses. Surprisingly, a short contig of Fusarium graminearum virus-1 SD4 was also detected, indicating that intergeneric transmission of the viruses may exist. Besides an understanding in the virome diversity, the mycovirome survey provides the first clue of biological molecules that can be further developed for antifungal purposes.

Diaporthe helianthi与D. gulyae是导致向日葵（Helianthus annuus L.）茎腐病（Phomopsis stem canker）的病原真菌，该病是美国向日葵产量受限的重要真菌病害。在本研究中，通过从美国明尼苏达州、内布拉斯加州、北达科他州和南达科他州商业田地中随机采集的病态向日葵植株中分离得到的52个和42个分别针对D. gulyae和D. helianthi的分离株，对这两种病原真菌进行了霉病毒的研究。从每个真菌中提取的总RNA样本，经rRNA去除了的样本，被合并构建了一个测序库，采用元转录组学方法获得了每个库20GB的原始读数。在这两个库之间，仅共享一种含量较高的霉病毒。分别发现了感染D. gulyae和D. helianthi的21个和10个新型病毒片段，以及一个被检测为黄瓜绿斑病毒外壳蛋白的植物病毒片段，这表明了同种病毒在不同界间的传播。在感染D. helianthi的病毒中，我们检测到了之前在直接向日葵病毒组中报道过的两种相同的病毒，即向日葵叶关联的分节病毒3型和5型。有趣的是，一种主要被认为是昆虫病毒的Qinvirus，在一段片段中被发现。此外，在D. gulyae库中还检测到了一种线性的单链DNA病毒片段，除了单链（+）RNA、单链（-）RNA和双链RNA病毒外。令人惊讶的是，还检测到了一小段小麦赤霉病菌病毒-1 SD4的片段，这表明病毒可能在属间传播。除了对病毒组多样性有深入了解之外，霉病毒调查还为抗真菌目的进一步开发的生物分子提供了首个线索。