Effects Of Overexpression Of The Mutants Of Torsin Protein Of Spodoptera Frugiperda On Infection Of Autographa Californica Multiple Nucleopolyhedrovirus

Baculoviruses are a group of large double-stranded DNA envelope viruses.Currently,these viruses are used as biosafe pesticides and expression vectors and widely applied in pest biological control,foreign gene expression and mammalian cells transduction.Autographa californica multiple nucleopolyhedrovirus(Ac MNPV)is the most studied baculovirus and serve as the type species in the genus of alphabaculovirus.During infection,the budded virions(BVs)of Ac MNPV enter host cells by clathrin-mediated endocytosis.In the cytoplasm,the nucleocapsids are transported to the nucleus with the aid of virus-induced actin cable.After passage through the nuclear pore complex(NPC),the virus initiates the DNA replication and nucleocapsid assembly.Then,a subset of progeny nucleocapsids egresses from nuclear membrane and buds through plasma membrane to form BVs.In the infection cycle,the interaction of Ac MNPV and host nuclear membrane-related factors is not clear.In eukaryotic cells,Torsin is the only member of the AAA ATPase family that is localized both in the endoplasmic reticulum(ER)and the nuclear membrane and may function in regulating nuclear membrane remodeling and NPC formation.In this study,to determine the potential roles of host Torsin in Ac MNPV infection,we firstly isolated the ORF of Spodoptera frugiperda Torsin.Sequence analysis revealed that mammalian animals(such as humans)encode 5 Trosin proteins,whereas nematodes and insects,the lower eukaryotes,only encode a single Torsin protein.The ORF of S.frugiperda Torsin is 1053 bp and predicted to a protein with the molecular weight of 40.02 k Da.Transcriptional analysis showed that the transcript level of Torsin in Ac MNPV-infected cells remained at a relatively high level during 1-18 h post-infection(p.i.).Transient overexpression of the dominant-negative(DN)forms of Torsin in Sf9 cells resulted in a dramatic reduction of the production of infectious BVs.This suggested that cellular Torsin is involved in Ac MNPV infection.Using the recombinant Ac MNPV bacmid to overexpress the DN forms of Torsin,we found that Torsin is not required for the egress of Ac MNPV BVs.We proposed that Torsin may be required for the early stage of Ac MNPV infection,such as the virus entry into nucleus.The functional roles of Torsin in Ac MNPV infection are needed for further investigation.