Fungal peptide destruxin a plays a specific role in suppressing the innate immune response in Drosophila melanogaster

Destruxins are a class of insecticidal, anti-viral and phytotoxic cyclic depsipeptides that are also studied for their toxicity to cancer cells. They are produced by various fungi and a direct relationship has been established between Destruxin production and the virulence of the entomopathogen Metarhizium anisopliae. Aside from opening calcium channels, their in vivo mode of action during pathogenesis remains largely uncharacterized. To better understand the effects of a destruxin, we looked at changes in gene expression following injection of Destruxin A into the fruit fly Drosophila melanogaster. Microarray results revealed reduced expression of various antimicrobial peptides (AMPs) that play a major role in the fly’s humoral immune response. Flies co-injected with a non-lethal dose of Destruxin A and the normally innocuous Gram-negative bacteria Escherichia coli, showed increased mortality and an accompanying increase in bacterial titers. Mortality due to sepsis was rescued through ectopic activation of components in the IMD pathway, one of two signal transduction pathways that are responsible for AMP induction. These results demonstrate a novel role for Destruxin A in specific suppression of the humoral immune response in insects. Keywords: Gene Expression Gene expression 4 hours after injection of sub-lethal doses of Destruxin A compared to PBS controls, was examined in this experiment for adult Drosophila melanogaster.