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Schlagwörter:
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Zusammenfassung:
Horizontal gene transfer (HGT), the acquisition of novel genes and gene turnover are of utmost importance for genome evolution. The analysis of these processes requires genome-level studies of related species in a well-established phylogenetic framework. The nematode Pristionchus pacificus is a model system in evolutionary biology with genetic and transgenic tools that in nature is found in a necromenic association with scarab beetles. We have isolated and keep more than 160 P. pacificus ecotypes and 24 different Pristionchus species from around the world in the lab. In addition, we have isolated strains from 13 other genera of the family of the Diplogasteridae and their phylogenetic relationship has been revealed. P. pacificus constitutes a good starting point for the analysis of HGT. For example, seven members of the glycosyl hydrolase 5 family are found in its genome and cellulase activity has been observed in the supernatant of its cultures. Likewise, thousands of novel protein-coding genes were discovered in the genome sequence, that do not show any sequence similarity to the known protein universe yet are transcribed and cluster into gene families. To study the longevity and evolution of novel genes and those acquired by HGT, we used the 454 next-generation sequencing platform, to index the transcriptomes of 10 species (7 Pristionchus and 3 species of other genera). This approach is a rapid and cost-effective method to study nematode transcriptome complexity and the gene birth/death process within the genus Pristionchus. First, we could verify most of our initial discoveries in the P. pacificus genome sequence. For example, cellulase and diapausin genes are present in Pristionchus, but not in the outgroup species. We assigned HGT events to the most probable source organism and dated them to their respective last common ancestor. The dynamics of gene family evolution (e.g. gene turnover in the Cytochrome P450 family) was assessed in detail. The speed of arrival and departure of truly novel gene inventions could be estimated. We also speculate on the dependency of transcriptome complexity on nematode lifestyle or mode of sexual reproduction.
