Analysis of energetic amino acid metabolism inAcyrthosiphon pisum: A multidimensional approach to amino acid metabolism in aphids

Abstract

Aphids are highly specialized insects that feed on the phloem-sap of plants, the amino acid composition of which is very unbalanced. Amino acid metabolism is thus crucial in aphids, and we describe a novel investigation method based on the use of 14C-labeled amino acids added i n an artificial diet. A metabolism cage for aphids was constructed, allowing for the collection and analysis of the radioactivity incorporated into the aphid body, expired as COz, and rejected in the honeydew and exuviae. This method was applied to the study of the metabolism of eight energetic amino acids (aspartate, glutamate, glutamine, glycine, serine, alanine, proline, and threonine) in the pea aphid, Acyrthosiphon pisum. All these amino acids except threonine were subject to substantial catabolism as measured by high 14C02 production. The highest turnover was displayed by aspartate, with 60% of its carbons expired as COz. For the first time in an aphid, we directly demonstrated the synthesis of three essential amino acids (threonine, isoleucine, and lysine) from carbons of common amino acids. The synthesis of these three compounds was only observed from amino acids that were previously converted into glutamate. This conversion was important for aspartate, and lower for alanine and proline. To explain the quantitative results of interconversion between amino acids, we propose a compartmentation model with the intervention of bacterial endosymbiotes for the synthesis of essential amino acids and with glutamate as the only amino acid supplied by the insect to the symbiotes. Moreover, proline exhibited partial conversion into arginine, and it is suggested that proline is probably indirectly involved in excretory nitrogen metabolism. o 1995 WiIey-Liss, Inc.Key words: Homoptera, Aphididae, amino acid metabolism, symbiosis, radioactive labeling, essential amino acids, glutamate Acknowledgments: We thank G. Duport who helped with the insect cultures. We are grateful to Y. Rahbe and B. Delobel for helpful discussions and comments o n the manuscript. We also thank the Conseil Regional Rh6ne-Alpes for financial support.

Myzus persicaeSulzer aphid contains oxylipins that originate from phloem sap

“…It is reasonable to conclude that aphids are unable to synthesize oxylipins and take them up from the plant on which they are reared even if they contain the potential substrate to synthesize them (fatty acid profile corresponding to oxylipin profile with mainly C18:2 derivatives). Nevertheless, it is well known that artificial diets considerably perturb aphid metabolism (Febvay et al 1995) and could modify the synthesis of oxylipins for example by lack of substrate. The incubation of a crude aphid extract with radiolabeled substrate ( 14 C C18:2) revealed that the substrate is unchanged at the end of the reaction period and that no radioactivity can be detected at the retention times corresponding to the potential reaction products (HPOD and HOD).…”

“…Aphids were collected after 10 days by brushing them carefully from the leaves into liquid nitrogen before storage at (808C. Aphids were also reared on artificial diets during 10 days before storage at (808C (Febvay et al 1995). The diet contains 10 vitamins (amino benzoic acid, ascorbic acid, biotine, calcium chloride, choline chloride, folic acid, myo-inositol, nicotinic acid, pyroxidine and thiamine), 22 amino acids (alanine, b-alanine, arginine, asparagine, aspartic acid, cystein, glutamic acid, glutamine, glycine, histidine, isoleucine, leucine, lysine, methionine, ornithine, phenylalanine, proline, serine, threonine, tryptophan, tyrosine and valine) …”

“…Toxicity of 13-HOD and 13-HPOD were tested on aphids reared on oxylipin-complemented artificial diet (Febvay et al 1995). Four concentrations were used for each compound (0.15 nM, 1.5 nM, 15 nM and150 nM).…”

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

“…Genomic and physiological research reveals that Buchnera synthesizes essential amino acids for its host (6,7,(9)(10)(11)(12)). Buchnera's genome includes genes for almost all enzymes in the essential amino acid pathways and for enzymes in pathways for the nonessential amino acids tyrosine, glycine, and cysteine (6).…”

Putative evolutionary origin of plasmids carrying the genes involved in leucine biosynthesis in Buchnera aphidicola (endosymbiont of aphids)

“…aphidicola is thought to substantially contribute to the ability of aphids to thrive on plant sap, a diet of unbalanced composition that is notably poor in nitrogenous compounds (15,18,31,54). Various specific nutritional roles have been proposed, but there is strong experimental evidence only for bacterial supply of essential amino acids to the aphid (16,20,21,58). Tryptophan biosynthesis and provisioning have been studied in most detail and have rendered a coherent body of physiological, metabolic, and molecular genetic data.…”