Lateral gene transfer in nematodes
Abstracted from an article in Nematology Newsletter 49(4) 2003
Institute of Cell, Animal and Population Biology,
University of Edinburgh
Edinburgh EH9 3JT UK
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 inCaenorhabditis 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.
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