| Summary: | Immunological effectors of invasive species playing a role in addressing new colonization are still
poorly studied. In the present study the cDNA sequence of the defensin from a Lessepsian invasive
species, the Red Sea mussel Brachidontes pharaonis, was cloned using RACE method. Defensins
are a class of widely known antimicrobial peptides (AMPs), oligopeptides with a broad spectrum of
targeted organisms ranging from viruses to parasites. Analysis of BpDef sequence (262 bp) revealed
the presence of an ORF coding for 81 amino acids. The full-length amino acid sequence showed the
highest similarity to antimicrobial peptides MGD1 and MGD2 sequence from Mytilus galloprovincialis.
Phylogenetic analysis suggested that BpDef belongs to the αβ defensin AMPs with a typical domain
structurally characterized by a α helix and two β sheets. BpDef mRNA is located in circulating
hemocytes with small intra-cytoplasmic granules and with large granules. The transcription of defensin
gene was modulated by the stress from temperatures and oxygenation condition. Temperatures of 20
°C did not stimulate a BpDef transcription over a short time. At 30 °C the kinetics of BpDef gene
transcription showed up regulation after one day, while it was down regulated after six days, both
under normoxia and hypoxia conditions.
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