Abstract
Phylum Cnidaria is an ancient venomous group defined by the presence of cnidae, specialised organelles that serve as venom delivery systems. The distribution of cnidae across the body plan is linked to regionalisation of venom production, with tissue-specific venom composition observed in multiple actiniarian species. In this study, we assess whether morphological variants of tentacles are associated with distinct toxin expression profiles and investigate the functional significance of specialised tentacular structures. Using five sea anemone species, we analysed differential expression of toxin-like transcripts and found that expression levels differ significantly across tentacular structures when substantial morphological variation is present. Therefore, the differential expression of toxin genes is associated with morphological variation of tentacular structures in a tissue-specific manner. Furthermore, the unique toxin profile of spherical tentacular structures in families Aliciidae and Thalassianthidae indicate that vesicles and nematospheres may function to protect branched structures that host a large number of photosynthetic symbionts. Thus, hosting zooxanthellae may account for the tentacle-specific toxin expression profiles observed in the current study. Overall, specialised tentacular structures serve unique ecological roles and, in order to fulfil their functions, they possess distinct venom cocktails.
Highlights
Venom composition tends to be dynamic, varying across geographic locations and ontogenic stages, and between individuals in venomous taxa [1,2,3,4,5,6,7]
We sequenced and assembled the transcriptomes of five sea anemone species collected from Australian waters: C. adhaesivum, D. cf. armata, H. hemprichii, M. doreensis and P. semoni
More than 142 million paired-end reads were generated for M. doreensis, C. adhaesivum, D. cf. armata and P. semoni, while 240 million single-end reads were produced for H. hemprichii
Summary
Venom composition tends to be dynamic, varying across geographic locations and ontogenic stages, and between individuals in venomous taxa [1,2,3,4,5,6,7]. Differential expression of toxins across life stages and discrete anatomical regions has been reported across several taxa in the order Actiniaria (sea anemones) [13,14,15]. Different toxin profiles have been found in acrorhagi, tentacles, mesenterial filaments and body column [14,15], these tissue-specific toxin expression profiles vary across species. Sea anemone sodium channel inhibitory toxins were observed to be upregulated in the column of Anemonia sulcata and Heteractis crispa, but in the mesenterial filaments of Megalactis griffithsi and the acrorhagi of Actinia tenebrosa [14,15]. Multiple tentacle subtypes with distinct morphology and ecological roles may be present simultaneously within a species, suggesting that toxin expression profiles may be fine-tuned at an even greater level of detail
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