Abstract
In crustaceans, antimicrobial peptides (AMPs) are clustered into four major groups according to their amino acid composition and structure: (1) single-domain peptides containing cysteine residues such as anti-lipopolysaccharide-factor (ALF), (2) multi-domain or chimeric AMPs such as crustins, (3) non-conventional AMPs, and (4) linear single-domain AMPs. The majority of AMPs has been described in commercially exploited crustaceans, particularly decapods living in aquatic environments (crab, shrimp, lobster, and crayfish). Here, we aimed at establishing the AMPs repertoire of terrestrial isopods (Oniscidea), an original suborder of crustaceans adapted to life outside of the aquatic environment. Using transcriptomic data from 21 species, we identified 110 ALF and 73 crustin sequences. We also characterized the full-length sequence of armadillidins from 17 species, similar to the AMP previously described in the terrestrial isopod Armadillidium vulgare. Furthermore, we tested the antimicrobial activity of three armadillidin peptides characterized from three distantly related species. This analysis revealed similar activity spectra against pathogens, despite extensive structural variation among the tested peptides. In addition to conventional crustacean AMPs, our work highlights armadillidins as a new and independent family of AMPs specific to the Oniscidea, thus opening new perspectives concerning the study of the immune system of terrestrial isopods.
Highlights
Crustaceans form a large, ancient and extremely diverse animal group
Our analysis identified a total of 110 AFLs in the transcriptomes of the 21 terrestrial isopod species (Supplementary Table S2)
We identified 5.2 (±2.5) AFL transcripts per terrestrial isopod species on average, which is quite similar to the average number of ALF transcripts previously described in several crustacean species (6.2, ±3.3) (Figure 1)
Summary
Crustaceans form a large, ancient and extremely diverse animal group. After insects, they are by far the most numerous and widespread animals on Earth. Crustaceans are primarily marine organisms and they constitute a large proportion of the biomass of oceans [1], but there are freshwater, semi-terrestrial and terrestrial species. Over their long evolutionary history, crustaceans have been facing a wide variety of integrity challenges because their natural habitat is generally overloaded with infectious organisms, such as viruses, bacteria, fungi and other parasites [2]. Their evolutionary success confirms the effective strategies they use to fight against any kind of disease-causing agents and parasites present in their environment. Since pathogens are a threat to their survival, crustaceans have evolved efficient mechanisms based on two specific and complementary immune responses that may contribute to the elimination of invaders [3]: (i) the cellular response, resulting in phagocytosis of small particles and encapsulation of larger ones, and (ii) the humoral response involving the synthesis and the release of several
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