Horizontally Transferred Genes in Litopenaeus vannamei: Improvements in Energy Metabolism and Defense Mechanisms

A growing number of horizontally transferred genes (HTGs) have been detected as being transferred from prokaryotes to eukaryotes, most of them involving arthropods. In this study, we analyzed genome-wide horizontal gene transfer events in Pacific white shrimp Litopenaeus vannamei, as a member of the Arthropoda. The newly sequenced transcriptomes and ESTs provide the first opportunity for horizontal gene transfer (HGT) analysis. Combining homology searching and phylogenetic analysis, followed by experimental PCR determination, 14 HTGs were identified: 12 of them were transferred from bacteria and two from fungi. Unexpectedly, no HTGs of viral origin were found in L. vannamei genome. HTG structure analysis indicated that three introns have been inserted into two bacterial origin HTGs, and that the introns of two fungi originated HTGs were exchanged with shrimp-specific introns. Furthermore, three large DNA fragments were transferred into the L. vannamei genome along with the HTGs; the non-coding DNA sequences of two of the DNA fragments were removed when transfer into the shrimp genome. The results of the above HTGs structure analysis provided evidence of HGT events and implied that mature RNA was the substrate for HGT. Among 14 HTGs, six of them were annotated as energy metabolism-related, which may play important roles in supporting growth and development in shrimps. Four of them were associated with defense mechanisms, which would help shrimps adapt to specialized biotic niches. Environmental adaptation is also an energy-consuming procedure; therefore, all these HTGs might improve on shrimps’ environmental adaptability.