The complete genome sequence of a third distinct baculovirus isolated from the true armyworm, Mythimna unipuncta, contains two copies of the lef-7 gene

Authors: Harrison, Robert - Bob; Mowery, Joseph; Rowley, Daniel; Bauchan, Gary; THEILMANN, DAVID - Agriculture And Agri-Food Canada; ROHRMANN, GEORGE - Oregon State University; ERLANDSON, MARTIN - Agriculture And Agri-Food Canada

Submitted to: Virus Genes
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/21/2017
Publication Date: 4/1/2018
Citation: Harrison, R.L., Mowery, J.D., Rowley, D.L., Bauchan, G.R., Theilmann, D.A., Rohrmann, G.F., Erlandson, M.A. 2018. The complete genome sequence of a third distinct baculovirus isolated from the true armyworm, Mythimna unipuncta, contains two copies of the lef-7 gene. Virus Genes. 54(2):297-310.

Interpretive Summary: The true armyworm is a widespread pest of graminaceous crops and pastures. Viruses that infect and kill larvae of the true armyworm had previously been identified from a USDA Forest Service virus collection. To obtain a more complete understanding of the genetic factors regulating the insecticidal activity of true armyworm viruses, the entire genomic DNA sequence of one of these viruses was determined and analyzed. Features of the genome indicated that this virus was part of a larger group of viruses that infect other armyworms. A unique feature of this virus is that it contains two copies of a gene that redirects host cellular anti-virus proteins towards helping the virus make copies of itself. The information in this study contributes to progress towards developing ecologically safe and environmentally friendly virus-based insecticides to control damaging outbreaks of true armyworm, and will be of interest to those in academia, government, and industry who work with this group of insect viruses or with true armyworm and its management.

Technical Abstract: A baculovirus isolate from a USDA Forest Service collection was examined by electron microscopy and analysis of its genome sequence. The isolate, formerly referred to as Pseudoletia (Mythimna) sp. nucleopolyhedrovirus #7 (MyspNPV#7), was determined by barcoding PCR to derive from the host species Mythimna unipuncta (true armyworm) and was renamed Mythimna unipuncta nucleopolyhedrovirus #7 (MyunNPV#7). The occlusion bodies (OBs) and virions exhibited a size and morphology typical for OBs produced by species of genus Alphabaculovirus, with occlusion-derived virions consisting of 2 – 5 nucleocapsids within a single envelope. The MyunNPV#7 genome was determined to be 148,482 bp with a 48.58% G+C nucleotide distribution. A total of 159 ORFs were annotated in the genome sequence, including the 38 core genes of family Baculoviridae. The genome contained six homologous repeat regions (hrs) consisting of multiple copies of a 35-bp imperfect palindrome. Phylogenetic inference from baculovirus core gene amino acid sequence alignments placed MyunNPV#7 with group II alphabaculoviruses isolated from other armyworm and cutworm host species of lepidopteran family Noctuidae. MyunNPV#7 could be distinguished from other viruses in this group on the basis of differences in gene content and order. Pairwise nucleotide distances suggested that MyunNPV#7 represents a distinct species in Alphabaculovirus. The MyunNPV#7 genome was found to contain two copies of the late expression factor-7 (lef-7) gene, a feature not reported for any other baculovirus genome to date. Both copies of lef-7 encoded an F-box domain, which is required for the function of LEF-7 in baculovirus DNA replication.