The sf32 Unique Gene of Spodoptera frugiperda Multiple Nucleopolyhedrovirus (SfMNPV) Is a Non-Essential Gene That Could Be Involved in Nucleocapsid Organization in Occlusion-Derived Virions

Abstract

A recombinant virus lacking the sf32 gene (Sf32null), unique to the Spodoptera frugiperda multiple nucleopolyhedrovirus (SfMNPV), was generated by homologous recombination from a bacmid comprising the complete viral genome (Sfbac). Transcriptional analysis revealed that sf32 is an early gene. Occlusion bodies (OBs) of Sf32null contained 62% more genomic DNA than viruses containing the sf32 gene, Sfbac and Sf32null-repair, although Sf32null DNA was three-fold less infective when injected in vivo. Sf32null OBs were 18% larger in diameter and contained 17% more nucleocapsids within ODVs than those of Sfbac. No significant differences were detected in OB pathogenicity (50% lethal concentration), speed-of-kill or budded virus production in vivo. In contrast, the production of OBs/larva was reduced by 39% in insects infected by Sf32null compared to those infected by Sfbac. The SF32 predicted protein sequence showed homology (25% identity, 44% similarity) to two adhesion proteins from Streptococcus pyogenes and a single N-mirystoylation site was predicted. We conclude that SF32 is a non-essential protein that could be involved in nucleocapsid organization during ODV assembly and occlusion, resulting in increased numbers of nucleocapsids within ODVs.

Ha83, a Chitin Binding Domain Encoding Gene, Is Important to Helicoverpa armigera Nucleopolyhedrovirus Budded Virus Production and Occlusion Body Assembling

“…Interestingly, Ha83KO OBs were 25% larger in diameter than those of the complete virus and the shape of the occlusion bodies changed into a cuboid, whereas a 100 fold decrease in the average amount of DNA or ODVs per OB was observed in the larger occlusion bodies of ha83 deleted HearNPV mutants. A similar diameter increase happened in sf32 deleted SpfrMNPV, with enlargement of OBs and the nucleocapsids content reported to be 17% more in the larger sf32 knockout SpfrMNPV OBs 26 . Other genes, such as ac23 , modify the number of nucleocapsids per OB without affecting the number of occluded ODVs 30 31 .…”

“…5 ). Most of the structural gene deletion mutants, such as ha81 , ac93 , and bm95 thoroughly block the BV production without disrupting viral DNA replication 10 22 23 ; some reported baculovirus-host interaction genes, such as ha132, ac68 , sf32 , or bm79 , do not affect the BV production and viral DNA replication simultaneously after deletion 24 25 26 27 ; besides, some special gene knockout mutants would increase the BV production, for example, fp25k and ha107 28 29 . However, deletion of ha83 resulted in an 84% decrease in BV infectivity of the bacmid virus and a 134 fold increase of DNA replicates, this peculiar change is different from any other previously reported characterized baculovirus genes, and the reasons remain unclear.…”

Nucleopolyhedrovirus Coocclusion Technology: A New Concept in the Development of Biological Insecticides

“…These proteins tend to be highly conserved among NPVs. Of the genes involved in ODV composition, ac23 (F-protein), ac78 and sf32 have been demonstrated to influence the number of nucleocapsids (genomes) enveloped in each ODV ( Yu et al, 2009 ; Beperet et al, 2013 ; Li et al, 2014 ). In contrast, ac78 , ac132 and sf29 influence the number or type of ODVs occluded within OBs ( Simón et al, 2008 ; Li et al, 2014 ; Yang et al, 2014 ), whereas fp25k ( ac61 ) affects the occlusion of ODVs in cell culture conditions ( Cheng et al, 2012 ).…”