Antimicrobial peptides (AMPs) of lizards: a first comprehensive characterization of beta-defensins, ovo-defensins and cathelicidins from the Balearic lizard Podarcis lilfordi and closely related Lacertidae species

Abstract

Reptiles are remarkably resistant to infections, providing a critical system to understand diversity and evolution of the innate immune defense and its major players, the antimicrobial peptides (AMPs). Here we present the first comprehensive characterization of AMPs in the family Lacertidae with the objective of understanding their diversity and patterns of evolution. By means of extensive genome mining, we first obtained a nearly complete catalogue of antimicrobial proteins from the Balearic lizard Podarcis lilfordi: 65 beta-defensins (BDs), eight ovo-defensins (OVODs), encompassing three proline-rich proteins (OVOD-PrAMPs), and four cathelicidins (CATHs). Using this fine-scale annotation we retrieved corresponding orthologues and closed paralogues from published Lacertidae species, P. muralis, P. raffonei and Zootoca vivipara (58 total AMPs). Comparative sequence analysis indicated that all AMPs consistently locate in chromosome 3 (BDs and OVODs) and chromosome 12 (CATHs), supporting a monophyletic origin of the reptilian antimicrobial defense. In P. lilfordi, the AMPs are arranged in clusters of mostly contiguous peptides, flanked by highly conserved marker proteins. All Lacertidae AMPs present a multiple exon structure (two to four) and a characteristic cysteine motif (six-cysteines in BDs, eight in OVODs and four in CATHs), consistently with previous findings in vertebrates. Comparative analyses support an ongoing process of gene expansion via duplication in tandem of both BDs and OVODs, whereas OVOD-PrAMPs and CATHs mostly present a one-to-one ortholog in all species. Despite this remarkable intra-genomic diversity, we also found multiple examples of distant species sharing identical or nearly identical peptides, providing clear evidence of convergent evolution. Overall, these findings substantially increased our understanding of AMP diversity and evolution in reptiles and set the basis to explore adaptive polymorphism maintenance and mechanisms of antimicrobial defense.