Gene structure of phospholipase A2 associated with cellular immune responses in Tribolium castaneum

Phospholipase (A₂) (PLA₂) is the committed catalytic step of eicosanoid biosynthesis, which has been a common molecular target of several entomopathogens to induce insect immunosuppression. Despite critical importance of (PLA₂) in insect immunity, its gene structure was not known. Based on a previous study that an immune-associated (PLA₂) in insect is secretory type of (PLA₂) (sPLA₂), five highly matched cDNA sequences were obtained from (T). (castaneum) genome database using a (sPLA₂) sequence probe encoded in (Drosophila) (melanogaster) and their expression were confirmed by reverse transcriptase polymerase chain reaction. All five (PLA₂) showed a specific activity. An immunofluorescence assay indicated that a (TcPLA₂) was localized near to cellular membrane of the hemocytes cytosol at immune challenge. (T) (castaneum) larvae could exhibit nodulation reaction in response to bacterial challenge, which clearly inhibited in larvae treated with double stranded RNAs of the five (TcPLA₂s). Addition of arachidonic acid (the catalytic product of (PLA₂)) to the dsRNA-treated larvae rescued the inhibition of nodule formation. These results suggest that all five (TcPLA₂) genes are associated with insect immune reaction.