Cloning of mRNA sequences for two antibacterial peptides in a hemipteran insect, Riptortus clavatus

Escherichia coli injection rapidly induced bactericidal activity in the hemolymph of a hemipteran insect, Riptortus clavatus. This activity reached its maximum at 9 hr after injection and thereafter declined slowly. Two types of cDNA clones involved in this response were isolated by differential screening. The predominant type encoded for an open reading frame of 678 amino acids, which consisted of fourteen tandem repeats. Each repeat was rich in charged residues and had a proline-rich region which had striking sequence similarities to proline-rich antibacterial peptides from other insect species, indicating these clones encode a multipeptide precursor of antibacterial peptides. The other type encoded for a glycine-rich peptide similar to a known antibacterial peptide as well. Northern blot analyses revealed rapid induction of mRNAs corresponding to these clones after the injection. To our knowledge, this is the first report on the mRNA sequences of antibacterial peptides of hemimetabolous insects, and the second report on the occurrence of multipeptide precursor structure in insect antibacterial peptides.