The Autographa californica Multiple Nucleopolyhedrovirus ac51 Gene Is Required for Efficient Nuclear Egress of Nucleocapsids and Is Essential for In Vivo Virulence

Abstract

Alphabaculoviruses are lepidopteran-specific nucleopolyhedroviruses that replicate within the nucleus; however, the anterograde transport of the nucleocapsids of these viruses, which is an obligatory step for progeny virion production, is not well understood. In the present study, a uniqueAlphabaculovirusgene with unknown function, namely, the Autographa californica multiple nucleopolyhedrovirus (AcMNPV)ac51gene, was found to be required for efficient nuclear egress of AcMNPV nucleocapsids. Our results indicate thatac51is a late gene, and Ac51 protein was detectable from 24 to 72 h postinfection using an antibody raised against Ac51. Ac51 is distributed in both the cytoplasm and nuclei of infected cells. Uponac51deletion, budded virion (BV) production by 96 h posttransfection was reduced by approximately 1,000-fold compared with that of wild-type AcMNPV. Neither viral DNA synthesis nor viral gene expression was affected. Ac51 was demonstrated to be a nucleocapsid protein of BVs, andac51deletion did not interrupt nucleocapsid assembly and occlusion-derived virion (ODV) formation. However, BV production in the supernatants of transfected cells during a viral life cycle was substantially decreased whenac51was deleted. Further analysis showed that, compared with wild-type AcMNPV,ac51deletion decreased nucleocapsid egress, while the numbers of nucleocapsids in the nuclei were comparable. Deletion ofac51also eliminated the virulence of AcMNPVin vivo. Taken together, our results support the conclusion thatac51plays an important role in the nuclear egress of nucleocapsids during BV formation and is essential for thein vivovirulence of AcMNPV.

Autographa californica Multiple Nucleopolyhedrovirusorf13is Required for Efficient Nuclear Egress of Nucleocapsids

“…The results showed that ac13 deletion did not affect nucleocapsid assembly or progression of viral infection into very late phases to form OBs, but impaired efficient egress of nucleocapsids from the nucleus to the cytoplasm. (15). In this study, the genes required for the nuclear egress of nucleocapsids and production of BVs seemed to be divided into two categories (15): (i) genes whose deletion did not affect nucleocapsid assembly but prevented nuclear egress of nucleocapsids, thus abrogating BV production and also interrupting OB formation, and (ii) genes whose deletion did not affect nucleocapsid assembly but decreased the efficiency of nuclear egress of nucleocapsids, thus decreasing BV production but not affecting OB formation.…”

“…and Ac142 are required for nucleocapsid egress (14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25). Deletion of ac11, ac75, ac78, gp41, ac93, p48, or ac142 abrogated egress of nucleocapsids from the nucleus.…”

“…The BV life cycle includes replication of viral DNA, assembly of progeny nucleocapsids, egress from the nucleus, transport through the cytoplasm, and budding from the plasma membrane where the BV gains its envelope. To determine whether reduced vAc ac13KO -ph BV production resulted from a defect in viral DNA replication, viral DNA replication was compared between bAc ac13KO -ph-and bAc-ph-transfected cells by quantitative PCR (qPCR) within 24 h p.t., before secondary infection by BVs could occur (15). Sf9 cells were transfected with equal amounts of bAc ac13KO -ph or bAc-ph bacmid DNA and collected at 0, 12 and 24 h p.t.. Total intracellular DNA was extracted and treated with DpnI to eliminate input bacmid DNA.…”

“…The TEM analysis was used to assess whether ac13 deletion had any effect on egress. According to methods previously reported (15,16,24), we counted and compared the numbers of intranuclear and egressed nucleocapsids in 20 randomly chosen cells infected with vAc ac13KO -ph, vAc ac13REP -ph or vAc-ph. The egressed nucleocapsids included nucleocapsids exiting the nuclear membrane, in transport through the cytoplasm and budding from the cytoplasmic membrane ( Fig.…”

A Conserved Phenylalanine Residue of Autographa Californica Multiple Nucleopolyhedrovirus AC75 Protein Is Required for Occlusion Body Formation

“…According to a previous report, AcMNPV nucleocapsid egress involves actin-based movement within nuclear envelope protrusions, which is coupled with localized nuclear envelope disruption and viral release into the cytoplasm (Ohkawa and Welch, 2018). Currently, several AcMNPV genes (ac11, ac13, ac51, ac66, ac78, gp41, ac93, p48, exon0, and p49) have been identified to be required for nuclear egress (Fang et al, 2007;Ke et al, 2008;McCarthy et al, 2008;Yuan et al, 2008Yuan et al, , 2011Tao et al, 2013Tao et al, , 2015Biswas et al, 2017;Li et al, 2018;Qiu et al, 2019;Chen et al, 2020). Deletion of these genes does not affect viral genome replication and progeny nucleocapsid assembly but restrains or blocks the egress of progeny nucleocapsids from the nucleus to the cytoplasm.…”