Pristionchus pacificus nutrigenomics
Adaptation of organisms to environmental change may be facilitated by the creation of new genes. New genes without homologs in other lineages are known as taxonomically-restricted orphan genes and may result from divergence or de novo formation. Previously, we have extensively characterized the evolution and origin of such orphan genes in the nematode model organism Pristionchus pacificus. Here, we employ large-scale transcriptomics to establish potential functional associations and to measure the degree of transcriptional plasticity among orphan genes. Specifically, we performed RNA-seq experiments of P. pacificus worms grown on monoxenic cultures of 24 different bacteria. Based on coexpression analysis, we identified 28 large modules that harbor 3,727 diplogastrid-specific orphan genes and that respond dynamically to different bacteria. These coexpression modules have distinct regulatory architecture and also exhibit differential expression patterns across development suggesting a link between bacterial response networks and development. Gene age analysis revealed a considerably higher number of family- and even species-specific orphan genes in certain coexpression modules. This indicates that new genes are not attached randomly to existing cellular networks and that integration can happen very fast. Integrative analysis of protein domains, gene expression and ortholog data facilitated the assignments of biological labels for 22 coexpression modules with the largest, fast-evolving module being associated with spermatogenesis. In summary, this work presents the first functional annotation for thousands of P. pacificus orphan genes and reveals insights into their integration into environmentally responsive gene networks.