Reference genome sequences of Mythimna separata (Lepidoptera: Noctuidae)

Abstract

Lepidopteran insects are an important group of animals, among which some are used as biochemical and physiological model species in the insect and silk industries, whereas others are major agricultural pests. Therefore, genome sequences of several lepidopteran insects have been reported thus far. The oriental armyworm, Mythimna separata, is an agricultural pest commonly used to study insect immune reactions and interactions with parasitoid wasps as hosts. To improve our understanding of these research topics, reference genome sequences were constructed in the present study. Using long-read and short-read sequence data, de novo assembly and polishing were performed, and haplotigs were purged. Subsequently, gene predictions and functional annotations were performed. To search for orthologs of the Toll and immune deficiency (IMD) pathways and C-type lectins, annotation data analysis, BLASTp, and Hummer scans were performed. The M. separata genome is 682 Mbp; its contig N50 was 2.7 Mbp with 21,970 genes and 24,452 coding sites predicted. All orthologs of the core components of the Toll and IMD pathways and 105 C-type lectins were identified. These results suggest that the genome data were of sufficient quality as reference genome data and could contribute to promoting M. separata and lepidopteran research at the molecular and genome levels. Simple SummaryThe oriental armyworm, Mythimna separata, an agricultural pest, is commonly used to study insect immune reactions and interactions with parasitoid wasps. To promote such studies, a reference genome was constructed. The M. separata genome is 682Mbp long--a size comparable to that of other lepidopteran insects. The contig N50 value of the genome is 2.7 Mb, which indicates sufficient quality to be used as reference genome data. Gene set data were constructed using genome and RNA-sequencing data; a total of 21,970 genes and 24,452 coding sites were predicted. Functional gene annotation was performed using the predicted amino acid sequences and reference gene set data of the model organism and other insect species as well as Unigene and Pfam datasets. Consequently, 45-80% of the amino acid sequences were annotated using these data sets. Using these data, most of the orthologs of core components in the Toll and immune deficiency (IMD) pathways were identified, suggesting the presence of these two pathways in M. separata. Additionally, 105 C-type lectins were identified in the M. separata genome, which were more numerous than those in other insect species, suggesting that these genes may be duplicated.