The complete mitochondrial genome of the fall webworm, Hyphantria cunea (Lepidoptera: Arctiidae)

Abstract

The complete mitochondrial genome (mitogenome) of the fall webworm, Hyphantria cunea (Lepidoptera: Arctiidae) was determined. The genome is a circular molecule 15 481 bp long. It presents a typical gene organization and order for completely sequenced lepidopteran mitogenomes, but differs from the insect ancestral type for the placement of tRNA(Met). The nucleotide composition of the genome is also highly A + T biased, accounting for 80.38%, with a slightly positive AT skewness (0.010), indicating the occurrence of more As than Ts, as found in the Noctuoidea species. All protein-coding genes (PCGs) are initiated by ATN codons, except for COI, which is tentatively designated by the CGA codon as observed in other lepidopterans. Four of 13 PCGs harbor the incomplete termination codon, T or TA. All tRNAs have a typical clover-leaf structure of mitochondrial tRNAs, except for tRNA(Ser)(AGN), the DHU arm of which could not form a stable stem-loop structure. The intergenic spacer sequence between tRNA(Ser)(AGN) and ND1 also contains the ATACTAA motif, which is conserved across the Lepidoptera order. The H. cunea A+T-rich region of 357 bp is comprised of non-repetitive sequences, but harbors several features common to the Lepidoptera insects, including the motif ATAGA followed by an 18 bp poly-T stretch, a microsatellite-like (AT)(8) element preceded by the ATTTA motif, an 11 bp poly-A present immediately upstream tRNA(Met). The phylogenetic analyses support the view that the H. cunea is closerly related to the Lymantria dispar than Ochrogaster lunifer, and support the hypothesis that Noctuoidea (H. cunea, L. dispar, and O. lunifer) and Geometroidea (Phthonandria atrilineata) are monophyletic. However, in the phylogenetic trees based on mitogenome sequences among the lepidopteran superfamilies, Papillonoidea (Artogeia melete, Acraea issoria, and Coreana raphaelis) joined basally within the monophyly of Lepidoptera, which is different to the traditional classification.

Keywords: Arctiidae; Fall webworm; Hyphantria cunea; Lepidoptera; Mitochondrial genome; Phylogeny.

Fig 1

Linear map of the mitogenome of Hyphantria cunea. The tRNAs are labeled according to the IUPAC-IUB single letter amino acid codes above the bar indicating coding sequence on major strand or below the bar showing on minor strand. One-letter symbol L, L*, S and S* denote codon tRNA^Leu(CUN), tRNA^Leu(UUR), tRNA^Ser(AGN), and tRNA^Ser(UCN), respectively. Underlined PCGs or rRNA genes are located on minor strand and PCGs that are not underlined are located on major strand. Overlapping lines (F1-F4) under the map denote four overlapping PCR fragments amplified for sequencing. The line at the lower left represents the map scale.

Fig 2

Alignment of initiation region for the cytochrome oxidase subunit I (COI) genes of lepidopteran insects. The Diptera insect Anopheles funestus was included due to fact that the translation initiation codon for the COI gene was determined by analysis of the transcript information analysis . The first four or five codons and their amino acids are shown on the right-hand side of the figure. Boxed nucleotides are the presumed translation initiators, which have been postulated as the initiation codon for COI in each species. Underlined nucleotides indicate the adjacent partial sequence of tRNA^Tyr. Arrows indicate the direction of transcription.

Fig 3

Inferred secondary structure of the 22 tRNAs of the Hyphantria cunea mitogenome. +, GT pairs; -, AT/GC pairs. The tRNAs are labeled with the abbreviations of their corresponding amino acids. Arms of tRNAs (clockwise from top) are the amino acid acceptor arm, the TψC arm, the anticodon arm, and the dihydrouridine arm.

Fig 3

Inferred secondary structure of the 22 tRNAs of the Hyphantria cunea mitogenome. +, GT pairs; -, AT/GC pairs. The tRNAs are labeled with the abbreviations of their corresponding amino acids. Arms of tRNAs (clockwise from top) are the amino acid acceptor arm, the TψC arm, the anticodon arm, and the dihydrouridine arm.

Fig 4

Alignment of the intergenic spacer region between tRNA^Ser(UCN) and ND1 of lepidopteran insects. The shaded ATACTAA motif was conserved across the Lepidoptera order.

Fig 5

The features present in the A+T-rich region of Hyphantria cunea. The sequence is shown in the N strand.

Fig 6

Phylogeny of lepidopteran insects. (A) Current hypothesis of lepidopteran superfamily relationships after Kristensen and Skalski (1999) . Phylogenetic trees inferred from amino acid sequences of 13 PCGs of the mitogenome by using MP analysis (B) and NJ analysis (C). Drosophila yakuba and Anopheles gambiae were used as outgroups. The numbers above branches specify bootstrap percentages (1000 replicates).