Mitochondrial Genome Sequence and Expression Profiling for the Legume Pod Borer Maruca vitrata (Lepidoptera: Crambidae) | Maruca vitrata Mitochdrial Genome and Expression
2011
Margam, Venu M. | Coates, Brad S. | Hellmich, Richard L. | Agunbiade, Tolulope | Seufferheld, Manfredo J. | Sun, Weilin | Ba, Malick N. | Sanon, Antoine | Binso-Dabire, Clementine L. | Baoua, Ibrahim | Ishiyaku, Mohammad F. | Covas, Fernando G. | Srinivasan, R. (Ramasamy) | Armstrong, Joel | Murdock, Larry L. | Pittendrigh, Barry R. | Smagghe, Guy
We report the assembly of the 14,054 bp near complete sequencing of the mitochondrial genome of the legume pod borer (LPB), Maruca vitrata (Lepidoptera: Crambidae), which we subsequently used to estimate divergence and relationships within the lepidopteran lineage. The arrangement and orientation of the 13 protein-coding, 2 rRNA, and 19 tRNA genes sequenced was typical of insect mitochondrial DNA sequences described to date. The sequence contained a high A+T content of 80.1% and a bias for the use of codons with A or T nucleotides in the 3rd position. Transcript mapping with midgut and salivary gland ESTs for mitochondrial genome annotation showed that translation from protein-coding genes initiates and terminates at standard mitochondrial codons, except for the cox I gene, which may start from an arginine CGA codon. The genomic copy of cox II terminates at a T nucleotide, and a proposed polyadenylation mechanism for completion of the 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 nd 4/ nd 4L and nd 6/ cyt b, and a tricistronic transcript for atp 8/ atp 6/ cox III. This processing of polycistronic mitochondrial transcripts adheres to the tRNA punctuated cleavage mechanism, whereby mature transcripts are cleaved only at intervening tRNA gene sequences. In contrast, the tricistronic atp 8/ atp 6/ cox III in Drosophila is present as separate atp 8/ atp 6 and cox III transcripts despite the lack of an intervening tRNA. Our results indicate that mitochondrial processing mechanisms vary between arthropod species, and that it is crucial to use transcriptional information to obtain full annotation of mitochondrial genomes.
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