Insect immunity. Septic injury of Drosophila induces the synthesis of a potent antifungal peptide with sequence homology to plant antifungal peptides.

In response to a septic injury (pricking with a bacteria-soaked needle) larvae and adults of Drosophila produce considerable amounts of a 44-residue peptide containing 8 cysteines engaged in intramolecular disulfide bridges. The peptide is synthesized in the fat body, a functional homologue of the mammalian liver, and secreted into the blood of the insect. It exhibits potent antifungal activity but is inactive against bacteria. This novel inducible peptide, which we propose to name drosomycin, shows a significant homology with a family of 5-kDa cysteine-rich plant antifungal peptides recently isolated from seeds of Brassicaceae. This finding underlines that plants and insects can rely on similar molecules in their innate host defense.