Submitted to: PLoS One
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/6/2014
Publication Date: 3/31/2014
Citation: Valles, S.M., Bell, S., Firth, A.E. 2014. Solenopsis invicta virus 3: mapping of structural proteins, ribosomal frameshifting, and similarities to Acyrthosiphon pisum virus and kelp fly virus. PLoS One. 9(3):e93497. Interpretive Summary: The red imported fire ant was introduced into the United States in the 1930s and currently infests about 300 million acres. It is estimated to cause $3-5 billion in annual economic losses to livestock and agricultural production and poses a serious threat to human health. Biological control is widely considered the most sustainable method of controlling the fire ant over its entire range. The virus, Solenopsis invicta virus 3, discovered by USDA-ARS scientists at the Center for Medical, Agricultural and Veterinary Entomology (CMAVE, Gainesville, FL), has been shown to be a promising potential biocontrol agent for these ants. However, characterization of this virus is crucial to its development as a microbial insecticide. Scientists at CMAVE and the University of Cambridge, Cambridge, United Kingdom have completed the first studies to characterize the unique replication strategy of this virus. Furthermore, their research findings suggest creation of a new virus order to taxonomically place the virus. This information will advance our understanding of this and related viruses, and provide information necessary to its development as a microbial insecticide.
Technical Abstract: Solenopsis invicta virus 3 (SINV-3) is a positive-sense single-stranded RNA virus that infects the red imported fire ant, Solenopsis invicta. We show that the second open reading frame (ORF) of the dicistronic genome is expressed via a frameshifting mechanism and that the sequences encoding the structural proteins map to both ORF2 and the 3' end of ORF1, downstream of the sequence that encodes the RNA-dependent RNA polymerase. The genome organization and structural protein expression strategy resemble those of Acyrthosiphon pisum virus (APV), an aphid virus. The capsid protein that is encoded by the 3' end of ORF1 in SINV-3 and APV is predicted to have a jelly-roll fold similar to the capsid proteins of picornaviruses and caliciviruses. The capsid-extension protein that is produced by frameshifting, includes the jelly-roll fold domain encoded by ORF1 as its N-terminus, while the C-terminus encoded by the 5' half of ORF2 has no clear homology with other viral structural proteins. A third protein, encoded by the 3' half of ORF2, is associated with purified virions at sub-stoichiometric ratios. Circumstantial evidence suggests that both viruses likely utilize a subgenomic RNA to express their structural proteins, but this has not been experimentally verified. Both SINV-3 and APV are unclassified picorna-like viruses distantly related to members of the order Picornavirales and the family Caliciviridae. Within this grouping, features of the genome organization and capsid domain structure of SINV-3 and APV appear more similar to caliciviruses, perhaps suggesting the basis for a Calicivirales order.