Lateral gene transfer in nematodes

Lateral gene transfer in nematodes

Abstracted from an article in Nematology Newsletter 49(4) 2003

Source article:

Mark Blaxter

Institute of Cell, Animal and Population Biology,

University of Edinburgh

Edinburgh EH9 3JT UK

mark.blaxter@ed.ac.uk

www.nematodes.org

Lateral or horizontal gene transfer (LGT) is an evolutionary mode that occurs in prokaryotes. However, LGT has also occurred in plant mitochondrial genomes (1) , so it is not confined to prokaryotes. Among eukaryotes, nematodes have been some of the best examples of LGT defined to date.

Blaxter et al have identified anomalous formate reductase and alcohol dehydrogenase genes in Caenorhabditis elegans that have a phylogenetic distribution strongly suggestive of a LGT event from fungi to nematodes (5).

Plant-parasitic nematodes of the Order Tylenchida invade plant tissues to establish feeding sites. Cellulases (endoglucanases) are a family of enzymes thought to be restricted to prokaryotes. Plant-cell wall digesters such as termites and ruminants use symbiotic and commensal bacteria to achieve this task. In plant-parasitic nematodes, however, the genes for endoglucanase are found in the nematode genome (6-9). These genes have clearly bacterial coding sequences. They are robustly grouped with bacterial genes in phylogenetic analyses, but are nuclear-encoded in nematodes and have standard spliceosomal introns.

Additional nematode genes with bacterial histories, such as nod factor genes (involved in nodule formation in legumes by bacterial symbionts), are being discovered in nematodes (11,12). It may be that these bacterial "parasitism genes" underpin the ecological success of many nematode groups.

References

1. Bergthorsson, U., Adams, K.L., Thomason, B. & Palmer, J.D. Widespread horizontal transfer of mitochondrial genes in flowering plants. Nature 424, 197-201 (2003).

2. Stanhope, M.J. et al. Phylogenetic analyses do not support horizontal gene transfers from bacteria to vertebrates. Nature 411, 940-4 (2001).

3. Salzberg, S.L., White, O., Peterson, J. & Eisen, J.A. Microbial genes in the human genome: lateral transfer or gene loss? Science 292, 1903-6 (2001).

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5. Parkinson, J. & Blaxter, M.L. SimiTri - visualising similarity relationships for large groups of sequences. Bioinformatics 19, 390-395 (2002).

6. Yan, Y., Smant, G. & Davis, E. Functional screening yields a new beta-1,4-endoglucanase gene from Heterodera glycines that may be the product of recent gene duplication. Mol Plant Microbe Interact 14, 63-71 (2001).

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9. Davis, E.L. et al. Nematode Parasitism Genes. Annu Rev Phytopathol 38, 365-396 (2000).

10. Parkinson, J., Mitreva, M., Hall, N., Blaxter, M. & McCarter, J.P. 400000 nematode ESTs on the Net. Trends Parasitol 19, 283-6 (2003).

11. McCarter, J.P. et al. Analysis and functional classification of transcripts from the nematode Meloidogyne incognita. Genome Biol 4, R26 (2003).

12. Scholl, E.H., Thorne, J.L., McCarter, J.P. & Bird, D.M. Horizontally transferred genes in plant-parasitic nematodes: a high-throughput genomic approach. Genome Biol 4, R39 (2003).

13. Blaxter, M.L. Genome sequencing: time to widen our horizons. Briefings in Functional Genomics and Proteomics 1, 7-9 (2002).