馬尼拉小繭蜂共生病毒表現微小核糖核酸干擾斜紋夜蛾類胰島素訊號路徑以抑制脂肪代謝

Abstract

寄生蜂作為天敵，透過毒液與共生病毒等多種機制影響寄主生理，確保自身幼蟲能在寄主體內存活與發育。多去氧核醣核酸病毒 (polydnaviruses, PDVs)為寄生蜂的共生病毒，能調控寄主的免疫、發育與能量代謝等生理狀態，以利寄生蜂幼蟲的生長與發育。研究指出，共生病毒可透過小分子核糖核酸 (如miRNA與siRNA)調節寄主基因表現，進一步改變其生理功能。昆蟲的能量代謝在此寄生關係中扮演重要角色，尤其是類胰島素訊號路徑 (Insulin/ insulin grow factor (IGF) signaling pathway)，是昆蟲體內高度保守的內分泌調控路徑，調控能量平衡、脂肪儲存與生長發育。脂肪不僅提供昆蟲生長、發育與免疫所需能量。對寄生蜂而言更為關鍵，因為寄生蜂幼蟲無法自行合成脂肪，故仰賴寄主提供脂肪作為能量來源。本研究欲了解寄生蜂是否能透過共生病毒影響寄主的類胰島素訊號傳遞，進一步調控脂肪合成，以馬尼拉小繭蜂與斜紋夜蛾為模式物種，探討共生病毒是否調控寄主的類胰島素訊號路徑，進而影響其脂肪代謝。我們以次世代定序技術 (next-generation sequencing, NGS) 分析馬尼拉小繭蜂共生病毒潛在表現微小核糖核酸 (micro RNA, miRNA) 寄主體內影響類胰島素訊號相關基因。接著透過定量聚合酶連鎖反應驗證這些基因在感染共生病毒後的表現變化，隨後分析感染後寄主體內胰島素訊號路徑終產物三酸甘油脂的含量。此外我們進一步合成miRNA類似物與抑制劑確認這些由共生病毒表現 miRNA之功能。研究結果顯示，當寄主斜紋夜蛾感染馬尼拉小繭蜂共生病毒後，類胰島素訊號路徑的基因表現顯著下降，抑制脂肪生合成，寄主體內三酸甘油脂 (triglyceride, TAG) 含量減少。病毒可能透過miRNA抑制寄主胰島素訊號路徑中的特定基因表現，進而影響脂肪儲存。這些結果進一步說明寄生蜂共生病毒可藉由影響寄主內分泌與能量代謝，使寄主處於能量缺乏狀態，進一步削弱免疫，從而間接為寄生蜂幼蟲的發育創造有利環境。本研究提供了寄生蜂如何透過共生病毒影響寄主能量代謝的新視角，並深化我們對寄生性天敵與寄主之間生理交互作用的理解。另外本研究也為昆蟲病理學與基因農藥的開發奠定理論基礎，未來可應用於害蟲的生物防治技術，如：透過核糖核酸干擾 (RNA interference, RNAi) 調控害蟲生理功能，進一步發展精準環保的害蟲防治管理策略。

Parasitoid wasps act as natural enemies and employ various mechanisms, such as venom and symbiotic viruses, to manipulate host physiology, thereby ensuring the survival and development of their larvae within the host. Polydnaviruses (PDVs), a group of symbiotic viruses associated with parasitoid wasps, play a crucial role in modulating host immunity, development, and energy metabolism to favor the growth and the development of wasp larvae. Studies have shown that PDVs can regulate host gene expression through small RNAs such as microRNAs (miRNAs), ultimately altering host physiological functions. Energy metabolism in insects plays a pivotal role in host-parasitoid interactions. In particular, the insulin/ insulin grow factor (IGF) signaling pathway is a highly conserved endocrine signaling pathway in insects, regulating energy balance, lipid storage, and development. Lipids are crucial for insect growth, development, and immune function. Still, they are also critical for parasitoid wasps, as their larvae are incapable of synthesizing de novo and rely on host-derived lipids as an energy source. This study aims to investigate whether parasitoid wasps can modulate the host’s insulin signaling pathway via their symbiotic viruses, thereby affecting lipid biosynthesis. Using Snellenius manilae and Spodoptera litura as model species, we investigate whether PDVs can regulate host insulin signaling pathways and alter lipid metabolism. We first employed next-generation sequencing to identify potential PDV-encoded miRNAs that may target host genes related to the insulin signaling pathway. We then used quantitative PCR (qPCR) to validate changes in gene expression following PDV infection and analyzed host triglyceride levels as a metabolic endpoint of the insulin signaling pathway. Furthermore, express miRNA mimics and inhibitors were applied to confirm the function of these PDV-derived miRNAs. Our results demonstrate that infection of ii S. litura by S. manilae PDVs significantly downregulates the expression of genes involved in the insulin signaling pathway, leading to suppressed lipid biosynthesis and a notable reduction in host triglyceride content. The virus likely achieves this by using miRNAs to suppress the expression of specific genes within the host insulin signaling pathway, thereby impairing lipid storage. These findings provide new insights into how PDVs manipulate host endocrine and metabolic systems to induce an energy-deficient state in the host, creating a more favorable environment for parasitoid larval development. This study enhances our understanding of the physiological interactions between parasitoid wasps and their hosts, offering a novel perspective on host-parasite interaction dynamics. Additionally, it lays the theoretical foundation for future insect pathology applications and RNA-based biopesticides development. Such strategies may be employed in pest control through the targeted regulation of pest physiology, contributing to advancing precise and environmentally friendly pest management technologies.