Tian et al. BMC Genomics 2010, 11:187 http://www.biomedcentral.com/1471-2164/11/187 Page 13 of 19 Figure 10 Gene duplication and structural diversity of AMPs in N. vitripennis. A. Gene duplication. Chromosome fragments are shown in lines and genes coding AMPs are represented by box, in which gray one stands for signal and pro-peptide and blue one indicates mature peptide. Introns are indicated in triangles with phase 1 in red, phase 2 in green, and phase 0 in cyan; B. Structural diversity in N. vitripennis AMPs. Changes in structure relative to classical insect defensins are circled. of nabaecin-3 is highly similar to A. mellifera abaecin (41.2% (protein) or 45.1% (DNA)), while its CtNU shares 41.4% (protein) and 56.2% (DNA) identity to navitripeni- cin. And the sequence identity extends to their 3’ UTRs (Figure 12A). At the genomic level, all these three genes retain a conserved phase 0 intron at identical positions (Figure 5), indicating that they are evolutionarily related. In all these genes, CtNU and navitripenicin are encoded by a single exon. Therefore, we assume that after the wasp diverged from the bee lineage, an exon-shuffling, mediated by the conserved phase 0 intron, occurred between the ancestral ortholog of the A. mellifera abae- cin and a duplicated navitripenicin gene, which resulted in the emergence of the first nabaecin gene. In subse- quent evolution, a multigene family of three members formed by gene duplication (Figure 12B). basic evolutionary scenarios are recognized in the gen- eration of a complex antimicrobial system in N. vitripen- nis. Our work presented here will offer a basic platform for further studying the immunological and evolutionary significances of these newly discovered AMPs in parasi- tic insects. Whether these AMP-like genes with a com- plicate structure or much more copies are involved in parasitism remains an open question which constitutes our next research direction. In particular, our efficient approaches for finding new AMPs in a genomic scale can easily be applied to other model organisms includ- ing humans, which will accelerate our understandings on AMP-mediated innate immunity at a defense net- work level. Further functional characterization of these parasitic wasp-derived AMPs will also help explore new- type of drug leads for anti-infective therapy. Conclusions By using a combined computational and experimental strategy, we established for the first time the N. vitripen- nis peptidome associated with innate immunity. Three Methods Database searches Strategies for gene discovery used here are provided in the supplementary information (see additional file 1).