Katsuma Susumu, Kawamoto Munetaka, Shoji Keisuke, Aizawa Takahiro, Kiuchi Takashi, Izumi Natsuko, Ogawa Moe, Mashiko Takaaki, Kawasaki Hideki, Sugano Sumio, Tomari Yukihide, Suzuki Yutaka, Iwanaga Masashi
Department of Agricultural and Environmental Biology, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Bunkyo-ku, Tokyo 113-8657, Japan.
Department of Agrobiology and Bioresources, School of Agriculture, Utsunomiya University, Utsunomiya-shi, Tochigi 321-8505, Japan.
DNA Res. 2018 Jan 17;25(3):277-86. doi: 10.1093/dnares/dsx056.
Bombyx mori macula-like virus (BmMLV) is a positive, single-stranded insect RNA virus that is closely related to plant maculaviruses. BmMLV is currently characterized as an unclassified maculavirus. BmMLV accumulates at extremely high levels in cell lines derived from the silkworm, Bombyx mori, but it does not lead to lethality and establishes persistent infections. It is unknown how this insect maculavirus replicates and establishes persistent infections in insect cells. Here, we showed that BmMLV p15, which is located on a subgenomic fragment and is not found in plant maculaviruses, is highly expressed in BmMLV-infected silkworm cells and that p15 protein is required to establish BmMLV infections in silkworm cells. We also showed that two distinct small RNA-mediated pathways maintain BmMLV levels in BmMLV-infected silkworm cells, thereby allowing the virus to establish persistent infection. Virus-derived siRNAs and piRNAs were both produced as the infection progressed. Knockdown experiments demonstrated that the exogenous RNAi pathway alone or RNAi and piRNA pathways function cooperatively to silence BmMLV RNA and that both pathways are important for normal growth of BmMLV-infected silkworm cells. On the basis of our study, we propose a mechanism of how a plant virus-like insect virus can establish persistent infections in insect cells.
家蚕黄斑样病毒（BmMLV）是一种正链单链昆虫RNA病毒，与植物黄斑病毒密切相关。BmMLV目前被归类为未分类的黄斑病毒。BmMLV在源自家蚕（Bombyx mori）的细胞系中以极高水平积累，但它不会导致细胞死亡，并能建立持续性感染。目前尚不清楚这种昆虫黄斑病毒如何在昆虫细胞中复制并建立持续性感染。在此，我们发现位于亚基因组片段上且在植物黄斑病毒中不存在的BmMLV p15，在受BmMLV感染的家蚕细胞中高度表达，并且p15蛋白是在蚕细胞中建立BmMLV感染所必需的。我们还发现，两种不同的小RNA介导途径维持受BmMLV感染的家蚕细胞中的BmMLV水平，从而使病毒能够建立持续性感染。随着感染的进展，病毒来源的siRNA和piRNA均会产生。敲低实验表明，单独的外源性RNAi途径或RNAi与piRNA途径协同作用使BmMLV RNA沉默，并且这两种途径对于受BmMLV感染的家蚕细胞的正常生长都很重要。基于我们的研究，我们提出了一种植物病毒样昆虫病毒如何在昆虫细胞中建立持续性感染的机制。
