Submitted to: PLoS One
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/20/2010
Publication Date: 2/2/2011
Citation: Margam, V.M., Coates, B.S., Hellmich II, R.L., Agunbiade, T., Seufferheld, M.J., Sun, W., Ba, M.N., Sanon, A., Binso-Dabire, C.L., Baoua, I., Ishiyaku, M.F., Covas, F.G., Srinivasan, R., Armstrong, J., Murdock, L.L., Pittendrigh, B.R. 2011. Mitochondrial genome sequence and expression profiling for the legume pod borer Maruca vitrata (Lepidoptera: Crambidae). PLoS One. 6(2):e16444. Interpretive Summary: The larval stage of moth species that feed upon fruit- and seed-bearing portions of crop plants threaten producer viability worldwide. Controlling these pest insect species in developing nations and within sub-tropical regions of the United States is especially difficult due to long crop growing seasons and multiple generations of the pest itself. Understanding insect pest biology and ecology will assist in devising ecologically friendly methods of control, and likely will increase the use of biotechnology in developing nations. To address these issues, we investigated the structure and gene expression of the legume pod borer, Maruca vitrata, mitochondrial genome. This species has a sub-tropical distribution and causes severe damage to legume crops in Hawaii and the U.S. territory of Puerto Rico. We show that distinct differences in expression are present among genes involved in metabolic pathways of the species when compared to model organisms. These results may affect the ability of this species to move and migrate within the field, and affect scientific recommendations regarding management of resistance of this insect when cowpea that express insecticidal toxins from Bacillus thuringiensis (Bt) are released for commercial use. This information will be useful to scientists interested in using Bt crops to control insect pests, especially in the tropical regions of the United States.
Technical Abstract: We report on the assembly of the 14,146 base pairs (bp) near complete mitochondrial sequencing of the legume pod borer (LPB), Maruca vitrata (Lepidoptera: Crambidae), which was used to estimate divergence and relationships within the lepidopteran lineage. Arrangement and orientation of 13 protein coding, 2 ribosomal RNA (rRNA), and 19 sequenced transfer RNA (tRNA) genes was typical of insect mitochondrial DNA sequences described to date, and contained a high A+T content of 80.1% and bias for use of codons with A or T nucleotides in the 3rd position. Application of transcript mapping with midgut and salivary gland Expressed Sequence Tag (ESTs) was used for mitochondrial genome annotation, and showed that translation from protein coding genes initiate and terminate at standard mitochondrial codons, except for coxI that may start from an arginine cytosine guanosine adenosine (CGA) codon. The genomic copy of coxII terminates at a T nucleotide, and a proposed polyadenylation mechanism for completion of the thymidine adenosine adenosine (TAA) stop codon was confirmed by comparisons to EST data. EST contig data further showed that mature M. vitrata mitochondrial transcripts are monocistronic, except for bicistronic transcripts for overlapping genes nd4/nd4L and nd6/cytb, and tricistronic the atp8/atp6/coxIII. This processing of polycistronic mitochondrial transcripts adheres to the tRNA punctuated cleavage mechanism, whereby mature transcripts are cleaved only at intervening tRNA gene sequences. This appears to contrast with Drosophila, where the tricistronic atp8/atp6/coxIII is present as separate atp8/atp6 and coxIII transcripts despite lack of an intervening tRNA. Our results indicate that mitochondrial processing mechanisms vary between arthropod species, and that the use of transcriptional information is crucial in order to obtain full annotation information of mitochondrial genomes.