Genomic insight into the amino acid relations of the pea aphid, Acyrthosiphon pisum, with its symbiotic bacterium Buchnera aphidicola

Abstract

Abstracti mb_942 249..258The pea aphid genome includes 66 genes contributing to amino acid biosynthesis and 93 genes to amino acid degradation. In several respects, the pea aphid gene inventory complements that of its symbiotic bacterium, Buchnera aphidicola (Buchnera APS). Unlike other insects with completely sequenced genomes, the pea aphid lacks the capacity to synthesize arginine, which is produced by Buchnera APS. However, consistent with other insects, it has genes coding for individual reactions in essential amino acid biosynthesis, including threonine dehydratase and branched-chain amino acid aminotransferase, which are not coded in the Buchnera APS genome. Overall the genome data suggest that the biosynthesis of certain essential amino acids is shared between the pea aphid and Buchnera APS, providing the opportunity for precise aphid control over Buchnera metabolism.

Aphid genome expression reveals host–symbiont cooperation in the production of amino acids

“…Glutamine has limited potential as a source of amino groups for production of other amino acids, but, together with glutamate synthase (GltS), it provides a shuttle for incorporating ammonia into most amino acids through glutamate. No gene encoding GltS was noted in the aphid genome, however (8,13). Thus, the issue of nitrogen recycling is not resolved.…”

“…These genes have orthologs in other insects with sequenced genomes, in which they carry out other functions related to amino acid conversions, even though the complete pathways are absent. This widespread presence in insects and other animals makes it unclear whether their presence in the aphid genome indicates a specific role in the amino acid production capacities of bacteriocytes (8). In a study based on a limited number of expressed sequence tags (ESTs) from A. pisum bacteriocytes (14), transcripts were retrieved from only two of these complementary aphid genes (encoding enzymes 1.14.16.1 and 4.4.1.1 in the methionine and tyrosine pathways, respectively).…”

“…Conversely, these symbionts lack nonessential amino acid biosynthetic pathways; thus, the host must provide these amino acids to the symbiont (6). The best-studied model of this phenomenon is the symbiosis of the pea aphid, Acyrthosiphon pisum, and its bacterial endosymbiont, Buchnera aphidicola (4,(6)(7)(8).…”

“…Despite having genes for most steps in these pathways, Buchnera is missing particular genes in five essential amino acid pathways (leucine, isoleucine, valine, methionine, and phenylalanine), raising the question of how these amino acids are produced in this symbiotic system. The A. pisum genome contains genes hypothesized to carry out the functions corresponding to these missing steps (8,13). These genes have orthologs in other insects with sequenced genomes, in which they carry out other functions related to amino acid conversions, even though the complete pathways are absent.…”

Integrated Metabonomic−Proteomic Analysis of an Insect−Bacterial Symbiotic System

“…52 It remains to be established why alanine is depressed in antibiotictreated aphids, but the low tyrosine content can be explained by the aphid-mediated synthesis of this amino acid from phenylalanine, which is produced by B. aphidicola. 53 The impact of antibiotic treatment on the amino acid profile of aphids has been interpreted previously as limitation of aphid protein synthesis by the shortfall of essential amino acids derived from B. aphidicola, with the accumulation of nonessential amino acids, which are not limiting. 18 It has also been argued that nonessential amino acids are selectively degraded in antibiotic-treated aphids, generating ammonia; and the increased ammonia load is alleviated by its condensation with glutamate to form glutamine, via the enzyme glutamine synthetase.…”