1st Place: D3103: Insect genotype drives differential gene expression in a protective bacterial symbiont

Most insects associate with heritable microbial symbionts. Uncovering the factors that shift these symbioses along the mutualism-parasitism spectrum is critical to assess the impact of these symbionts on insect biology. Empirical studies implicate a role for host genotypic variation in these shifts, but the exact genetic mechanisms remain unknown. We use pea aphids, Acyrthosiphon pisum, and a gram negative facultative bacterial symbiont, Regiella insecticola, as a model system to address this issue. Regiella confers protection to aphids against Pandora neoaphidis, an entomopathogenic fungus. However, not all pea aphid genotypes harboring the same strain of Regiella gain protection against the fungus. Using Q-PCR, Fluorescence in situ Hybridization (FISH) microscopy, and RNAseq, we test various hypotheses about the role of host genetic variation in symbiont mediated protection. While symbiont titer and localization do not explain variation in fungal protection, we found that the host genotype substantially influences symbiont gene expression. We also found conspicuous activity from transposable elements that varied among host genotypes. Our results indicate that insect genetic background considerably influences symbiont gene expression in a way that could affect the outcomes of these associations. Future work will focus on further characterizing these differences and prospecting molecular mechanisms of protection against Pandora which are yet to be identified. These dynamic interactions among pea aphids, symbionts, and pathogens, provide a useful paradigm on how insects evolved to regulate their microbiomes.



Keywords: Pea aphids, symbiosis, entomopathogens, genotypic variation, RNAseq, evolution