Figure 2.

Hypothetical evolutionary scenario of the Mytilidae CS-αβ antimicrobial peptides, based on the presence/absence patterns observed in publicly available -omic data. In brief, an ancestral defensin-like gene is expected to have supported the prototypical structural scaffold for the development of all the CS-αβ AMPs currently found in extant mussel species. Mytilins are expected to have been originated by a gene duplication event that might have occurred within clade B (see Morton et al., 2019), after the split between Brachidontinae and Mytiseptiferinae from the other three subfamilies. The evolutionary origin of pseudomytilins is expected to have occurred much more recently, possibly soon after the split between the Mytilus and Trichomya lineages.