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Trading amino acids at the aphid-Buchnera symbiotic interface.

ABSTRACT: Plant sap-feeding insects are widespread, having evolved to occupy diverse environmental niches despite exclusive feeding on an impoverished diet lacking in essential amino acids and vitamins. Success depends exquisitely on their symbiotic relationships with microbial symbionts housed within specialized eukaryotic bacteriocyte cells. Each bacteriocyte is packed with symbionts that are individually surrounded by a host-derived symbiosomal membrane representing the absolute host-symbiont interface. The symbiosomal membrane must be a dynamic and selectively permeable structure to enable bidirectional and differential movement of essential nutrients, metabolites, and biosynthetic intermediates, vital for growth and survival of host and symbiont. However, despite this crucial role, the molecular basis of membrane transport across the symbiosomal membrane remains unresolved in all bacteriocyte-containing insects. A transport protein was immunolocalized to the symbiosomal membrane separating the pea aphid Acyrthosiphon pisum from its intracellular symbiont Buchnera aphidicola The transporter, A. pisum nonessential amino acid transporter 1, or ApNEAAT1 (gene: ACYPI008971), was characterized functionally following heterologous expression in Xenopus oocytes, and mediates both inward and outward transport of small dipolar amino acids (serine, proline, cysteine, alanine, glycine). Electroneutral ApNEAAT1 transport is driven by amino acid concentration gradients and is not coupled to transmembrane ion gradients. Previous metabolite profiling of hemolymph and bacteriocyte, alongside metabolic pathway analysis in host and symbiont, enable prediction of a physiological role for ApNEAAT1 in bidirectional host-symbiont amino acid transfer, supplying both host and symbiont with indispensable nutrients and biosynthetic precursors to facilitate metabolic complementarity.

SUBMITTER: Feng H

PROVIDER: S-EPMC6690024 | biostudies-literature | 2019 Aug

REPOSITORIES: biostudies-literature

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Trading amino acids at the aphid-<i>Buchnera</i> symbiotic interface.

Feng Honglin H Edwards Noel N Anderson Catriona M H CMH Althaus Mike M Duncan Rebecca P RP Hsu Yu-Ching YC Luetje Charles W CW Price Daniel R G DRG Wilson Alex C C ACC Thwaites David T DT

Proceedings of the National Academy of Sciences of the United States of America 20190723 32

Plant sap-feeding insects are widespread, having evolved to occupy diverse environmental niches despite exclusive feeding on an impoverished diet lacking in essential amino acids and vitamins. Success depends exquisitely on their symbiotic relationships with microbial symbionts housed within specialized eukaryotic bacteriocyte cells. Each bacteriocyte is packed with symbionts that are individually surrounded by a host-derived symbiosomal membrane representing the absolute host-symbiont interface ...[more]

PMID: 31337682

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Project description:BackgroundMany insects host their obligate, maternally transmitted symbiotic bacteria in specialized cells called bacteriocytes. One of the best-studied insect nutritional endosymbioses is that of the aphid and its endosymbiont, Buchnera aphidicola. Aphids and Buchnera are metabolically and developmentally integrated, but the molecular mechanisms underlying Buchnera transmission and coordination with aphid development remain largely unknown. Previous work using electron microscopy to study aphid asexual embryogenesis has revealed that Buchnera transmission involves exocytosis from a maternal bacteriocyte followed by endocytotic uptake by a blastula. While the importance of exo- and endocytic cellular processes for symbiont transmission is clear, the molecular mechanisms that regulate these processes are not known. Here, we shed light on the molecular mechanisms that regulate Buchnera transmission and developmental integration.ResultsWe present the developmental atlas of ACYPI000536 and ACYPI008904 mRNAs during asexual embryogenesis in the pea aphid, Acyrthosiphon pisum. Immediately before Buchnera invasion, transcripts of both genes were detected by whole-mount in situ hybridization in the posterior syncytial nuclei of late blastula embryos. Following Buchnera invasion, expression of both genes was identified in the region occupied by Buchnera throughout embryogenesis. Notably during Buchnera migration, expression of both genes was not concomitant with the entirety of the bacterial mass but rather expression colocalized with Buchnera in the anterior region of the bacterial mass. In addition, we found that ACYPI000536 was expressed in nuclei at the leading edge of the bacterial mass, joining the bacterial mass in subsequent developmental stages. Finally, quantitative reverse transcription real-time PCR suggested that early in development both transcripts were maternally provisioned to embryos.ConclusionsWe venture that ACYPI000536 and ACYPI008904 function as nutrient sensors at the site of symbiont invasion to facilitate TOR-pathway-mediated endocytosis of Buchnera by the aphid blastula. Our data support earlier reports of bacteriocyte determination involving a two-step recruitment process but suggest that the second wave of recruitment occurs earlier than previously described. Finally, our work highlights that bacteriocyte-enriched amino acid transporter paralogs have additionally been retained to play novel developmental roles in both symbiont recruitment and bacteriome development.

Dataset Information

Trading amino acids at the aphid-Buchnera symbiotic interface.

Publications

Trading amino acids at the aphid-<i>Buchnera</i> symbiotic interface.

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