KARR, T.L.: The microbe that roared: Wolbachia rescue of a lethal Drosophila mutation

Wolbachia is an intracellular microbe harbored by a wide variety of arthropods including Drosophila. By unknown mechanisms, Wolbachia alters host reproductive biology usually to increase its representation within a population. In Drosophila, Wolbachia is closely associated with gametic incompatibility and has undergone extensive intraspecific horizontal transfer in nature. Neither the molecular mechanism of incompatibility nor the genetic interactions between host and microbe responsible for its persistence are known. In this report we describe the effect of Wolbachia on two alleles of the insulin receptor substrate gene, chico, recently implicated in the insulin-receptor pathway of growth regulation in Drosophila. Both lines containing the chico¹ and chico² alleles were found infected with Wolbachia and its removal significantly reduced the viability of chico homozygotes. In the most severe case, removal of infection “phenoconverted” chico² to lethality. chico² viability was restored upon reintroduction of Wolbachia either via microinjection or backcrossing into an infected maternal cytoplasm. The degree of rescue was dependent on the levels of Wolbachia present. This unique rescue suggests Wolbachia interacts either directly with chico or with elements of the insulin receptor pathway. This is the first demonstration of genetic interaction between Wolbachia and host signaling pathways, and expands the repertoire of host/symbiont interactions observed in this system. These results call into question the fundamental nature of Wolbachia symbiosis and suggests robust evolutionary dynamics not previously appreciated.