CDNA cloning and gene expression of defensin, an antibacterial peptide from a beetle, Allomyrina dichotoma (Coleoptera: Scarabaeidae)

Based on the amino acid sequence of Allomyrina dichotoma defensin, degenerate primers were synthesized, RT-PCR was done to clone a defensin cDNA and a 114-bp fragment was obtained. The complete nucleotide sequence was determined by sequencing the extended cDNA clone by 3' and 5' RACE. The deduced amino acid sequence of the mature portion was identical to that of the purified defensin. Tissue-specific gene expression analyzed by Northern blotting showed that the main sites for defensin gene expression were the fat bodies and hemocytes. The time course of defensin gene expression indicated that expression peaked at 8 to 12 h in larvae injected with Escherichia coli. An analysis of defensin gene expression induction by E. coli or Staphylococcus aureus in the fat body and hemocyte by RT-FCR showed that E. coli induces defensin gene expression more effectively than S. aureus in both tissues.