Abstract
BackgroundWe report the sequencing, assembly and analysis of the genome of the Komodo dragon (Varanus komodoensis), the largest extant lizard, with a focus on antimicrobial host-defense peptides. The Komodo dragon diet includes carrion, and a complex milieu of bacteria, including potentially pathogenic strains, has been detected in the saliva of wild dragons. They appear to be unaffected, suggesting that dragons have robust defenses against infection. While little information is available regarding the molecular biology of reptile immunity, it is believed that innate immunity, which employs antimicrobial host-defense peptides including defensins and cathelicidins, plays a more prominent role in reptile immunity than it does in mammals. .ResultsHigh molecular weight genomic DNA was extracted from Komodo dragon blood cells. Subsequent sequencing and assembly of the genome from the collected DNA yielded a genome size of 1.6 Gb with 45x coverage, and the identification of 17,213 predicted genes. Through further analyses of the genome, we identified genes and gene-clusters corresponding to antimicrobial host-defense peptide genes. Multiple β-defensin-related gene clusters were identified, as well as a cluster of potential Komodo dragon ovodefensin genes located in close proximity to a cluster of Komodo dragon β-defensin genes. In addition to these defensins, multiple cathelicidin-like genes were also identified in the genome. Overall, 66 β-defensin genes, six ovodefensin genes and three cathelicidin genes were identified in the Komodo dragon genome.ConclusionsGenes with important roles in host-defense and innate immunity were identified in this newly sequenced Komodo dragon genome, suggesting that these organisms have a robust innate immune system. Specifically, multiple Komodo antimicrobial peptide genes were identified. Importantly, many of the antimicrobial peptide genes were found in gene clusters. We found that these innate immunity genes are conserved among reptiles, and the organization is similar to that seen in other avian and reptilian species. Having the genome of this important squamate will allow researchers to learn more about reptilian gene families and will be a valuable resource for researchers studying the evolution and biology of the endangered Komodo dragon.
Highlights
We report the sequencing, assembly and analysis of the genome of the Komodo dragon (Varanus komodoensis), the largest extant lizard, with a focus on antimicrobial host-defense peptides
The collected Komodo dragon white blood cells were divided evenly, with half being processed for the isolation of genomic Deoxyribonucleic acids (DNA) in preparation for sequencing and library generation, and the other half reserved for mRNA extraction for our proteomic studies
It is notable that four peptides (VkBD10, VkBD28, VkBD30 and VkBD34) are predicted to be weakly cationic or neutral (+ 0.5–0) at pH 7, while nine peptides (VkBD3, VkBD4, VkBD11, VkBD19, VkBD23, VkBD26, VkBD35, VkBD36 and VkBD37) are predicted to be weakly to strongly anionic. These findings suggest while these peptides exhibit canonical βdefensin structural features and reside in β-defensin gene clusters, one or more of these genes may not encode for β-defensin-like peptides or canonical β-defensins, because β-defensins typically are cationic and their positive charge contributes towards their antimicrobial activity
Summary
Assembly and analysis of the genome of the Komodo dragon (Varanus komodoensis), the largest extant lizard, with a focus on antimicrobial host-defense peptides. The Komodo dragon diet includes carrion, and a complex milieu of bacteria, including potentially pathogenic strains, has been detected in the saliva of wild dragons They appear to be unaffected, suggesting that dragons have robust defenses against infection. Komodo dragon (Varanus komodoensis) is the world’s largest extant lizard, weighing up to 75–100 kg and measuring up to three meters in length This species of monitor lizard, indigenous to Komodo and nearby islands in southern Indonesia (Fig. 1), is a relic of very large varanids that once populated Indonesia and Australia, most of which, along with other megafauna, died out after the Pleistocene [1]. Komodo dragons are endangered and actively conserved in zoos around the world and in Komodo National Park, a UNESCO World Heritage site, due to their vulnerable status [2] They are believed to have evolved from other varanids in Australia, first appearing approximately 4 million years ago [1]. We hypothesized that Komodo dragons would have robust innate immunity and this innate immunity may be partially mediated by antimicrobial peptides
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