The Complete Mitochondrial Genome of the Entomopathogenic Nematode Steinernema carpocapsae: Insights into Nematode Mitochondrial DNA Evolution and Phylogeny |
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Authors: | Rafael Montiel Miguel A Lucena Jorge Medeiros Nelson Simões |
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Institution: | 1. CIRN and Department of Biology, University of the Azores, Ponta Delgada, A?ores, 9501-801, Portugal
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Abstract: | We determined the complete sequence of the mitochondrial DNA of the entomopathogenic nematode Steinernema carpocapsae and analyzed its structure and composition as well as the secondary structures predicted for its tRNAs and rRNAs. Almost
the complete genome has been amplified in one fragment with long PCR and sequenced using a shotgun strategy. The 13,925-bp
genome contains genes for 2 rRNAs, 22 tRNAs, and 12 proteins and lacks an ORF encoding ATPase subunit 8. Four initiation codons
were inferred, TTT, TTA, ATA, and ATT, most of the genes ended with TAA or TAG, and only two had a T as an incomplete stop
codon. All predicted tRNAs showed the nonconventional secondary structure typical of Secernentea. Although we were able to
fold the sequences of trnN, trnD, and trnC into more conventional cloverleaf structures after adding adjacent nucleotides, northern blot experiments showed that the
nonstandard tRNAs are actually expressed. Phylogenetic and comparative analyses showed that the mitochondrial genome of S. carpocapsae is more closely related to the genomes of A. suum and C. elegans than to that of Strongyloides stercoralis. This finding does not support the phylogeny based on nuclear small subunit ribosomal DNA sequences previously published.
This discrepancy may result from differential reproductive strategies and/or differential selective pressure acting on nuclear
and mitochondrial genes. The distinctive characteristics observed among mitochondrial genomes of Secernentea may have arisen
to counteract the deleterious effects of Muller’s ratchet, which is probably enhanced by the reproductive strategies and selective
pressures referred to above.
Electronic Supplementary Material Electronic Supplementary material is available for this article at
and accessible for authorised users.
Reviewing Editor: Dr. Rafael Zardoya] |
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Keywords: | Steinernema carpocapsae Nematode mtDNA rRNA tRNA Muller’ s ratchet Phylogeny |
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