Song Jingjiao, Wang Xi, Hou Dianhai, Huang Huachao, Liu Xijia, Deng Fei, Wang Hualin, Arif Basil M, Hu Zhihong, Wang Manli
State Key Laboratory of Virology, Wuhan Institute of Virology, Chinese Academy of Sciences, Wuhan 430071, P. R. China.
Experimental Medicine Center, Tongji Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan 430030, P. R. China.
PLoS One. 2016 Jul 25;11(7):e0159862. doi: 10.1371/journal.pone.0159862. eCollection 2016.
Baculoviruses are insect-specific pathogens with a generally narrow host ranges. Successful primary infection is initiated by the proper interaction of at least 8 conserved per os infectivity factors (PIFs) with the host's midgut cells, a process that remains largely a mystery. In this study, we investigated the host specificities of the four core components of the PIF complex, P74, PIF1, PIF2 and PIF3 by using Helicoverpa armigera nucleopolyhedrovirus (HearNPV) backbone. The four pifs of HearNPV were replaced by their counterparts from a group I Autographa californica multiple nucleopolyhedrovirus (AcMNPV) or a group II Spodoptera litura nucleopolyhedrovirus (SpltNPV). Transfection and infection assays showed that all the recombinant viruses were able to produce infectious budded viruses (BVs) and were lethal to H. armigera larvae via intrahaemocoelic injection. However, feeding experiments using very high concentration of occlusion bodies demonstrated that all the recombinant viruses completely lost oral infectivity except SpltNPV pif3 substituted pif3-null HearNPV (vHaBacΔpif3-Sppif3-ph). Furthermore, bioassay result showed that the median lethal concentration (LC50) value of vHaBacΔpif3-Sppif3-ph was 23-fold higher than that of the control virus vHaBacΔpif3-Hapif3-ph, indicating that SpltNPV pif3 can only partially substitute the function of HearNPV pif3. These results suggested that most of PIFs tested have strict host specificities, which may account, at least in part, for the limited host ranges of baculoviruses.
杆状病毒是昆虫特异性病原体，宿主范围通常较窄。成功的初次感染是由至少8种保守的经口感染性因子（PIFs）与宿主中肠细胞的适当相互作用引发的，这一过程在很大程度上仍是个谜。在本研究中，我们利用棉铃虫核多角体病毒（HearNPV）骨架研究了PIF复合体的四个核心组分P74、PIF1、PIF2和PIF3的宿主特异性。HearNPV的四个pif被来自I组苜蓿银纹夜蛾多核多角体病毒（AcMNPV）或II组斜纹夜蛾核多角体病毒（SpltNPV）的对应物所取代。转染和感染试验表明，所有重组病毒都能够产生感染性芽生病毒（BVs），并通过血腔注射对棉铃虫幼虫具有致死性。然而，使用非常高浓度的包涵体进行的喂食实验表明，除了SpltNPV pif3替代缺失pif3的HearNPV（vHaBacΔpif3-Sppif3-ph）外，所有重组病毒都完全丧失了经口感染性。此外，生物测定结果表明，vHaBacΔpif3-Sppif3-ph的半数致死浓度（LC50）值比对照病毒vHaBacΔpif3-Hapif3-ph高23倍，这表明SpltNPV pif3只能部分替代HearNPV pif3的功能。这些结果表明，所测试的大多数PIFs具有严格的宿主特异性，这可能至少部分解释了杆状病毒宿主范围有限的原因。
