Structural features of conopeptide genes inferred from partial sequences of the Conus tribblei genome

The evolvability of venom components (in particular, the gene-encoded peptide toxins) in venomous species serves as an adaptive strategy allowing them to target new prey types or respond to changes in the prey field. The structure, organization, and expression of the venom peptide genes may provide insights into the molecular mechanisms that drive the evolution of such genes. Conus is a particularly interesting group given the high chemical diversity of their venom peptides, and the rapid evolution of the conopeptide-encoding genes. Conus genomes, however, are large and characterized by a high proportion of repetitive sequences. As a result, the structure and organization of conopeptide genes have remained poorly known. In this study, a survey of the genome of Conus tribblei was undertaken to address this gap. A partial assembly of C. tribblei genome was generated; the assembly, though consisting of a large number of fragments, accounted for 2160.5 Mb of sequence. A large number of repetitive genomic elements consisting of 642.6 Mb of retrotransposable elements, simple repeats, and novel interspersed repeats were observed. We characterized the structural organization and distribution of conotoxin genes in the genome. A significant number of conopeptide genes (estimated to be between 148 and 193) belonging to different superfamilies with complete or nearly complete exon regions were observed, ~60 % of which were expressed. The unexpressed conopeptide genes represent hidden but significant conotoxin diversity. The conotoxin genes also differed in the frequency and length of the introns. The interruption of exons by long introns in the conopeptide genes and the presence of repeats in the introns may indicate the importance of introns in facilitating recombination, evolution and diversification of conotoxins. These findings advance our understanding of the structural framework that promotes the gene-level molecular evolution of venom peptides.