Aphid amino acid transporter regulates glutamine supply to intracellular bacterial symbionts

The ability of aphids to thrive on a phloem sap diet critically depends on their obligate symbiosis with the intracellular bacterium, Buchnera aphidicola.  Buchnera are housed and densely packed in specialized aphid bacteriocyte cells where they function to provide aphid hosts with essential nutrients that are absent in their diet.  Central to the aphid/Buchnera symbiosis is the exchange of amino acids between symbiotic partners, with Buchnera receiving non-essential amino acids from host aphids, and then synthesizing essential amino acids that are returned to the host.  With the aim of investigating symbiotic amino acid transport we utilized the A. pisum genome sequence and available transcriptomes to identify a total of 44 A. pisum amino acid transporters.  Gene expression analysis by quantitative-PCR identified a subset of 5 transporters that are highly expressed and/or highly enriched in bacteriocyte tissues and therefore implicated in amino acid transport at the symbiotic interface.  By functionally expressing and characterizing A. pisum symbiosis amino acid transporters in Xenopus laevis oocytes we are starting to gain further insight into symbiotic nutrient exchange.  Here, we identify a bacteriocyte glutamine transporter and show that glutamine transport is inhibited by essential amino acid arginine.  We propose a model were arginine accumulation within the bacteriocyte reduces glutamine transport to Buchnera, thereby regulating essential amino acid output from Buchnera.