Abstract
BackgroundHost/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 the A. pisum/Buchnera aphidicola symbiotic interface. Driven by amino acid concentration gradients, ApNEAAT1 moves proline, serine, and alanine from A. pisum to Buchnera and cysteine from Buchnera to A. pisum. Here, we test the hypothesis that ApNEAAT1 is localized to the symbiotic interface during asexual embryogenesis.ResultsDuring A. pisum asexual 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 asexual A. pisum are not equivalent. Future research is needed to elucidate the developmental time point at which the bacteriome reaches maturity.
Highlights
Host/symbiont integration is a signature of evolutionarily ancient, obligate endosymbioses
ApNEAAT1 protein does not colocalize with Buchnera during asexual embryogenesis Buchnera transmission occurs at stage 7 of asexual embryogenesis; earlier in development Buchnera is not present [23]
ApNEAAT1 did not localize to Buchnera, nor did it localize to the aphid-derived symbiosomal membrane that surrounds individual Buchnera cells
Summary
Host/symbiont integration is a signature of evolutionarily ancient, obligate endosymbioses. To advance under‐ standing 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 the A. pisum/Buchnera aphidicola symbiotic interface. Studying the developmental integration of Buchnera involves determining the mechanisms of transmission, bacteriocyte cellularization and bacteriome maturation, as well as how the function of the symbiosis changes across host development. Buchnera critically depend on their host bacteriocyte cells for energy and metabolic precursors that include most but not all non-essential amino acids [1, 18, 19]. Building on our earlier work, we further investigate the metabolic integration of Buchnera in the pea aphid, Acyrthosiphon pisum, across asexual embryogenesis
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