Functional genetic basis of Wolbachia-Drosophila endosymbiosis - Project Summary/Abstract The Russell Lab seeks to understand how bacterial symbionts of eukaryotic hosts are transmitted from one host generation to the next, and how these strategies evolve over time. Our research focuses on the intracellular inherited alphaproteobacterial Wolbachia symbionts of Drosophila melanogaster and congeners. These bacteria are capable of inducing a wide range of phenotypes in their hosts, from reproductive manipulations such as cytoplasmic incompatibility that bias offspring production towards infected females, to viral suppression that reduces titer and transmission from vector species to human populations. These phenotypes are currently employed to control host populations. However, little is known about the cellular, molecular, and evolutionary mechanisms underpinning these phenotypes or the transmission mechanisms that link Wolbachia between host generations. Over the next five years, we aim to reveal the microevolutionary processes driving host and symbiont evolution, the developmental processes that enable symbionts to induce their own host cell types, and the molecular mechanisms that link host and symbiont phenotypes using our in vivo and in vitro Wolbachia-infected Drosophila model system. To capture the rare and ephemeral horizontal transmission events that have occurred across Wolbachia’s evolutionary history, we will study diverse mixed strain infections in Drosophila cell lines and track their genome evolution. We will study the genomic basis of symbiont domestication after a host-switching event by leveraging historical stocks collected immediately after a Wolbachia strain entered and swept to fixation. We will study the downstream impacts of coevolutionary interactions by interrogating host and symbiont gene expression to identify novel symbiont-induced host developmental programs and molecular mechanisms. High-throughput genomic assays such as these have revealed promising candidate genes underlying Wolbachia’s ability to transmit to host offspring through the germline and infect uninfected cells efficiently. Using our in vivo and in vitro system, we will study the functional implications of these factors on the localization patterns of Wolbachia within and among host cells, Wolbachia’s ability to establish stable infections, and the fertility reinforcement phenotypes demonstrated by some strains. The overall vision for our research program is to develop a robust understanding of Wolbachia functional and evolutionary genetics in Drosophila to enable informed biological control applications. It is vital that we know the evolutionary genomic outcomes of divergent strains infecting novel hosts, as this is a possible outcome of releasing Wolbachia-infected mosquitoes into natural ecosystems. Our studies on the novel genetic regulatory and functional implications of host-symbiont molecular coevolution will reveal new biological pathways and mechanisms that could be leveraged for biomedical applications. Lastly, our approaches for functional genetic testing of candidate genes in Wolbachia-infected Drosophila cells and flies will enable us to validate host-symbiont interaction hypotheses and ascribe direct functions to Wolbachia genes.
