Vector transmission plays a primary role in the life cycle of viruses, and insects are the most common vectors. An important mode of vector transmission, reported only for plant viruses, is circulative nonpropagative transmission whereby the virus cycles within the body of its insect vector, from gut to salivary glands and saliva, without replicating. This mode of transmission has been extensively studied in the viral families Luteoviridae and Geminiviridae and is also reported for Nanoviridae The biology of viruses within these three families is different, and whether the viruses have evolved similar molecular/cellular virus-vector interactions is unclear. In particular, nanoviruses have a multipartite genome organization, and how the distinct genome segments encapsidated individually transit through the insect body is unknown. Here, using a combination of fluorescent in situ hybridization and immunofluorescence, we monitor distinct proteins and genome segments of the nanovirus Faba bean necrotic stunt virus (FBNSV) during transcytosis through the gut and salivary gland cells of its aphid vector Acyrthosiphon pisum FBNSV specifically transits through cells of the anterior midgut and principal salivary gland cells, a route similar to that of geminiviruses but distinct from that of luteoviruses. Our results further demonstrate that a large number of virus particles enter every single susceptible cell so that distinct genome segments always remain together. Finally, we confirm that the success of nanovirus-vector interaction depends on a nonstructural helper component, the viral protein nuclear shuttle protein (NSP), which is shown to be mandatory for viral accumulation within gut cells.IMPORTANCE An intriguing mode of vector transmission described only for plant viruses is circulative nonpropagative transmission, whereby the virus passes through the gut and salivary glands of the insect vector without replicating. Three plant virus families are transmitted this way, but details of the molecular/cellular mechanisms of the virus-vector interaction are missing. This is striking for nanoviruses that are believed to interact with aphid vectors in ways similar to those of luteoviruses or geminiviruses but for which empirical evidence is scarce. We here confirm that nanoviruses follow a within-vector route similar to that of geminiviruses but distinct from that of luteoviruses. We show that they produce a nonstructural protein mandatory for viral entry into gut cells, a unique phenomenon for this mode of transmission. Finally, noting that nanoviruses are multipartite viruses, we demonstrate that a large number of viral particles penetrate susceptible cells of the vector, allowing distinct genome segments to remain together.

中文翻译：

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多部分纳米病毒跨越其蚜虫载体的途径。

载体传播在病毒的生命周期中起主要作用，而昆虫是最常见的载体。仅针对植物病毒报道的一种重要的媒介传播方式是循环非传播性传播，即病毒在昆虫媒介体内从肠道到唾液腺和唾液循环而不会复制。这种传播方式已在黄病毒科和双子病毒科的病毒家族中进行了广泛研究，并且还报道了纳米病毒科。这三个家族的病毒生物学是不同的，尚不清楚病毒是否已经进化出相似的分子/细胞病毒-载体相互作用。特别地，纳米病毒具有多部分基因组组织，并且衣壳化的不同基因组片段如何分别穿过昆虫体转运尚不清楚。这里，使用荧光原位杂交和免疫荧光的组合，我们监测了纳米病毒蚕豆坏死特技病毒（FBNSV）的独特蛋白质和基因组片段，在通过其蚜虫载体Acyrthosiphon pisum FBsum FBNSV的肠道和唾液腺细胞转胞期间，通过前肠和主要唾液腺细胞，该途径类似于双生病毒，但不同于黄体病毒。我们的结果进一步证明，大量病毒颗粒进入每个易感细胞，因此不同的基因组片段始终保持在一起。最后，我们确认纳米病毒与载体相互作用的成功取决于非结构性辅助成分，即病毒蛋白核穿梭蛋白（NSP），重要提示仅针对植物病毒描述的一种有趣的载体传播方式是循环非繁殖性传播，其中病毒通过昆虫载体的肠道和唾液腺而没有复制。三个植物病毒家族以这种方式传播，但是病毒-载体相互作用的分子/细胞机制的细节缺失。对于被认为与蚜虫载体相互作用的纳米病毒而言，这是惊人的，其方式类似于黄腐病毒或双生病毒，但是缺乏经验证据。我们在这里确认纳米病毒遵循与双生病毒相似的载体内途径，但不同于黄病毒。我们显示，它们产生病毒进入肠道细胞所必需的非结构蛋白，这是这种传播方式的独特现象。最后，我们注意到纳米病毒是多部分病毒，我们证明了大量病毒颗粒会穿透载体的易感细胞，从而使不同的基因组片段保持在一起。