AbstractBackgroundHost/symbiont integration is a signature of evolutionarily ancient, obligate endosymbioses. However, little is known about the cellular and developmental mechanisms of host/symbiont integration at the molecular level. Many insects possess obligate bacterial endosymbionts that provide essential nutrients. To advance understanding of the developmental and metabolic integration of hosts and endosymbionts, we track the localization of a non-essential amino acid transporter, ApNEAAT1, across asexual embryogenesis in the aphid,Acyrthosiphon pisum. Previous work in adult bacteriomes revealed that ApNEAAT1 functions to exchange non-essential amino acids at theA. pisum/Buchnera aphidicolasymbiotic interface. Driven by amino acid concentration gradients, ApNEAAT1 moves proline, serine, and alanine fromA. pisumtoBuchneraand cysteine fromBuchneratoA. pisum. Here, we test the hypothesis that ApNEAAT1 is localized to the symbiotic interface during asexual embryogenesis.ResultsDuringA. pisumasexual embryogenesis, ApNEAAT1 does not localize to the symbiotic interface. We observed ApNEAAT1 localization to the maternal follicular epithelium, the germline, and, in late-stage embryos, to anterior neural structures and insect immune cells (hemocytes). We predict that ApNEAAT1 provisions non-essential amino acids to developing oocytes and embryos, as well as to the brain and related neural structures. Additionally, ApNEAAT1 may perform roles related to host immunity.ConclusionsOur work provides further evidence that the embryonic and adult bacteriomes of asexualA. pisumare not equivalent. Future research is needed to elucidate the developmental time point at which the bacteriome reaches maturity.