Facultative vertically transmitted symbionts are a common feature of insects that determine many aspects of their hosts’ phenotype. Our capacity to understand and exploit these symbioses is commonly compromised by the microbes unculturability and consequent lack of genetic tools, an impediment of particular significance for symbioses of pest and vector species. Previous work had established that insecticide susceptibility of the economically important pest of rice, the brown planthopper Nilaparvata lugens, was higher in field-collected lineages that carry Ca. Arsenophonus nilaparvatae. We established Ca. A. nilaparvatae into cell-free culture and used this to establish the complete closed genome of the symbiont. We transformed the strain to express GFP and reintroduced it to N. lugens to track infection in vivo. The symbiont established vertical transmission, generating a discrete infection focus towards the posterior pole of each N. lugens oocyte. This infection focus was retained in early embryogenesis before transition to a diffuse somatic infection in late N. lugens embryos and nymphs. We additionally generated somatic infection in novel host species, but these did not establish vertical transmission. Transinfected planthopper lines acquired the insecticide sensitivity trait, with associated downregulation of the P450 xenobiotic detoxification system of the host. Our results causally establish the role of the symbiont in increasing host insecticide sensitivity with implications for insecticide use and stewardship. Further, the culturability and transformation of this intracellular symbiont, combined with its ease of reintroduction to planthopper hosts, enables novel approaches both for research into symbiosis and into control of insect pest species.

中文翻译：

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接种培养的砷虫后，飞虱害虫的杀虫剂敏感性增加


兼性垂直传播共生体是昆虫的一个常见特征，它决定了宿主表型的许多方面。我们理解和利用这些共生体的能力通常会受到微生物不可培养性和随之而来的遗传工具缺乏的损害，这对于害虫和媒介物种的共生体来说是一个特别重要的障碍。以前的工作已经确定，在田间收集的携带 Ca. Arsenophonus nilaparvatae 的谱系中，具有重要经济意义的水稻害虫褐飞虱 Nilaparvata lugens 的杀虫剂敏感性更高。我们将 Ca. A. nilaparvatae 建立到无细胞培养物中，并使用它来建立共生体的完整封闭基因组。我们将菌株转化为表达 GFP 并将其重新引入 N. lugens 以跟踪体内感染。共生体建立了垂直传播，产生了一个离散的感染焦点，朝向每个 N. lugens 卵母细胞的后极。这种感染重点保留在早期胚胎发生中，然后在晚期 N. lugens 胚胎和若虫中转变为弥漫性体细胞感染。我们还在新的宿主物种中产生了体细胞感染，但这些并没有建立垂直传播。转染飞虱品系获得了杀虫剂敏感性状，并下调了宿主的 P450 外源性解毒系统。我们的结果因果地确定了共生体在增加宿主杀虫剂敏感性方面的作用，对杀虫剂的使用和管理产生了影响。此外，这种细胞内共生体的可培养性和转化，加上它易于重新引入飞虱宿主，为研究共生和控制害虫物种提供了新的方法。