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A unique genetic code change in the mitochondrial genome of the parasitic nematode Radopholus similis

Joachim Jacob (UGent) , Bartel Vanholme (UGent) , Thomas Van Leeuwen (UGent) and Godelieve Gheysen (UGent)
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Abstract
Background : Mitochondria (mt) contain their own autonomously replicating DNA, constituted as a small circular genome encoding essential subunits of the respiratory chain. Mt DNA is characterized by a genetic code which differs from the standard one. Interestingly, the mt genome of nematodes share some peculiar features, such as small transfer RNAs, truncated ribosomal RNAs and - in the class of Chromadorean nematodes - unidirectional transcription. Findings : We present the complete mt genomic sequence (16,791 bp) of the plant-parasitic nematode Radopholus similis (class Chromadorea). Although it has a gene content similar to most other nematodes, many idiosyncrasies characterize the extremely AT-rich mt genome of R. similis (85.4% AT). The secondary structure of the large (16S) rRNA is further reduced, the gene order is unique, the large non-coding region contains two large repeats, and most interestingly, the UAA codon is reassigned from translation termination to tyrosine. In addition, 7 out of 12 protein-coding genes lack a canonical stop codon and analysis of transcriptional data showed the absence of polyadenylation. Northern blot analysis confirmed that only one strand is transcribed and processed. Furthermore, using nucleotide content bias methods, regions for the origin of replication are suggested. Conclusion : The extraordinary mt genome of R. similis with its unique genetic code appears to contain exceptional features correlated to DNA decoding. Therefore the genome may provide an incentive to further elucidate these barely understood processes in nematodes. This comprehension may eventually lead to parasitic nematode-specific control targets as healthy mitochondria are imperative for organism survival. In addition, the presented genome is an interesting exceptional event in genetic code evolution.
Keywords
Organelle genome, nematode, genetic code evolution

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Chicago
Jacob, Joachim, Bartel Vanholme, Thomas Van Leeuwen, and Godelieve Gheysen. 2009. “A Unique Genetic Code Change in the Mitochondrial Genome of the Parasitic Nematode Radopholus Similis.” Bmc Research Notes 2.
APA
Jacob, J., Vanholme, B., Van Leeuwen, T., & Gheysen, G. (2009). A unique genetic code change in the mitochondrial genome of the parasitic nematode Radopholus similis. BMC RESEARCH NOTES, 2.
Vancouver
1.
Jacob J, Vanholme B, Van Leeuwen T, Gheysen G. A unique genetic code change in the mitochondrial genome of the parasitic nematode Radopholus similis. BMC RESEARCH NOTES. 2009;2.
MLA
Jacob, Joachim, Bartel Vanholme, Thomas Van Leeuwen, et al. “A Unique Genetic Code Change in the Mitochondrial Genome of the Parasitic Nematode Radopholus Similis.” BMC RESEARCH NOTES 2 (2009): n. pag. Print.
@article{2119561,
  abstract     = {Background : Mitochondria (mt) contain their own autonomously replicating DNA, constituted as a small circular genome encoding essential subunits of the respiratory chain. Mt DNA is characterized by a genetic code which differs from the standard one. Interestingly, the mt genome of nematodes share some peculiar features, such as small transfer RNAs, truncated ribosomal RNAs and - in the class of Chromadorean nematodes - unidirectional transcription.
Findings : We present the complete mt genomic sequence (16,791 bp) of the plant-parasitic nematode Radopholus similis (class Chromadorea). Although it has a gene content similar to most other nematodes, many idiosyncrasies characterize the extremely AT-rich mt genome of R. similis (85.4\% AT). The secondary structure of the large (16S) rRNA is further reduced, the gene order is unique, the large non-coding region contains two large repeats, and most interestingly, the UAA codon is reassigned from translation termination to tyrosine. In addition, 7 out of 12 protein-coding genes lack a canonical stop codon and analysis of transcriptional data showed the absence of polyadenylation. Northern blot analysis confirmed that only one strand is transcribed and processed. Furthermore, using nucleotide content bias methods, regions for the origin of replication are suggested.
Conclusion : The extraordinary mt genome of R. similis with its unique genetic code appears to contain exceptional features correlated to DNA decoding. Therefore the genome may provide an incentive to further elucidate these barely understood processes in nematodes. This comprehension may eventually lead to parasitic nematode-specific control targets as healthy mitochondria are imperative for organism survival. In addition, the presented genome is an interesting exceptional event in genetic code evolution.},
  articleno    = {192},
  author       = {Jacob, Joachim and Vanholme, Bartel and Van Leeuwen, Thomas and Gheysen, Godelieve},
  issn         = {1756-0500},
  journal      = {BMC RESEARCH NOTES},
  keyword      = {Organelle genome,nematode,genetic code evolution},
  language     = {eng},
  pages        = {10},
  title        = {A unique genetic code change in the mitochondrial genome of the parasitic nematode Radopholus similis},
  url          = {http://www.biomedcentral.com/content/pdf/1756-0500-2-192.pdf},
  volume       = {2},
  year         = {2009},
}