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Abstract:
Detrimental microbes caused the evolution of a great diversity of antimicrobial defenses in plants and animals. Here we show that the eggs of a solitary digger wasp, the European beewolf Philanthus triangulum, emit large amounts of the gaseous free radical nitric oxide (NO.) to protect themselves and their provisions, paralyzed honeybees, against mold fungi. Despite the extraordinary concentrations of nitrogen radicals (NO. and its oxidation product NO2.) in the brood cells (~1500ppm), NO. is synthesized from L-arginine by an NO-synthase (NOS) as in other animals. The beewolf NOS gene revealed no conspicuous differences to related species. However, due to alternative splicing, the NOS-mRNA in beewolf eggs lacks a 144bp exon near the regulatory domain. This preventive external application of high doses of NO. by seemingly defenseless wasp eggs represents an evolutionary key innovation that adds a remarkable novel facet to the array of functions of the important biological effector NO.
