title: Disruption of the baculovirus core gene ac78 results in decreased production of multiple nucleocapsid-enveloped occlusion-derived virions and the failure of primary infection in vivo.
abstract: The Autographa californica multiple nucleopolyhedrovirus (AcMNPV) ac78 gene is one of the baculovirus core genes. Recent studies showed that ac78 is essential for budded virion (BV) production and the embedding of occlusion-derived virion (ODV) into occlusion body during the AcMNPV life cycle. Here, we report that an ac78-knockout AcMNPV (vAc78KO) constructed in this study had different phenotypes than those described in the previous studies. A few infectious BVs were detected using titer assays, immunoblot analyses and plaque assays, indicating that ac78 is not essential for BV formation. Electron microscopy confirmed that the ac78 deletion did not affect nucleocapsid assembly and ODV formation. However, the numbers of multiple nucleocapsid-enveloped ODVs and ODV-embedded occlusion bodies were significantly decreased. Subsequently, the highly conserved amino acid residues 2-25 and 64-88 of Ac78, which are homologous to an oxidoreductase and cytochrome c oxidase, respectively, were demonstrated to play a crucial role in the morphogenesis of multiple nucleocapsid-enveloped ODV. Immunoblot analysis found that Ac78 was an ODV envelope-associated protein. Consistently, amino acid residues 56-93 of Ac78 were identified as an inner nuclear membrane sorting motif, which may direct the localization of Ac78 to the ODV envelope. In vivo infectivity assays showed that the occlusion bodies of vAc78KO were unable to establish primary infection in the midgut of Trichoplusia ni larvae. Taken together, our results suggest that ac78 plays an important role in BV production and proper multiple nucleocapsid-enveloped ODV formation, as well as AcMNPV primary infection in vivo.
authors.affiliation: State Key Laboratory of Biocontrol, Sun Yat-sen University, Guangzhou 510275, China; Department of Biology, Zhaoqing University, Zhaoqing 526061, China.
authors.forename: Sai-Nan
authors.initials: SN
authors.lastname: Li
authors.affiliation: State Key Laboratory of Biocontrol, Sun Yat-sen University, Guangzhou 510275, China.
authors.forename: Jin-Yu
authors.initials: JY
authors.lastname: Wang
authors.affiliation: State Key Laboratory of Biocontrol, Sun Yat-sen University, Guangzhou 510275, China.
authors.forename: Mei-Jin
authors.initials: MJ
authors.lastname: Yuan
authors.affiliation: State Key Laboratory of Biocontrol, Sun Yat-sen University, Guangzhou 510275, China. Electronic address: yangkai@mail.sysu.edu.cn.
authors.forename: Kai
authors.initials: K
authors.lastname: Yang
mesh_terms: D020816:Amino Acid Motifs; D000818:Animals; D009036:Moths / Q000821:virology*; D019251:Nucleocapsid / Q000235:genetics / Q000378:metabolism*; D017924:Nucleopolyhedroviruses / Q000737:chemistry / Q000235:genetics / Q000254:growth & development / Q000502:physiology*; D061987:Sf9 Cells; D014764:Viral Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D014771:Virion / Q000737:chemistry / Q000235:genetics / Q000254:growth & development / Q000502:physiology*; D019065:Virus Assembly; D057074:Virus Release
chemical_list: D014764:Viral Proteins
keywords: Budded virion; Inner nuclear membrane sorting motif; Multiple nucleocapsid-enveloped occlusion-derived virion; Primary infection; ac78