title: Pea aphid promotes amino acid metabolism both in Medicago truncatula and bacteriocytes to favor aphid population growth under elevated CO2.
abstract: Rising atmospheric CO(2) levels can dilute the nitrogen (N) resource in plant tissue, which is disadvantageous to many herbivorous insects. Aphids appear to be an exception that warrants further study. The effects of elevated CO(2) (750 ppm vs. 390 ppm) were evaluated on N assimilation and transamination by two Medicago truncatula genotypes, a N-fixing-deficient mutant (dnf1) and its wild-type control (Jemalong), with and without pea aphid (Acyrthosiphon pisum) infestation. Elevated CO(2) increased population abundance and feeding efficiency of aphids fed on Jemalong, but reduced those on dnf1. Without aphid infestation, elevated CO(2) increased photosynthetic rate, chlorophyll content, nodule number, biomass, and pod number for Jemalong, but only increased pod number and chlorophyll content for dnf1. Furthermore, aphid infested Jemalong plants had enhanced activities of N assimilation-related enzymes (glutamine synthetase, Glutamate synthase) and transamination-related enzymes (glutamate oxalate transaminase, glutamine phenylpyruvate transaminase), which presumably increased amino acid concentration in leaves and phloem sap under elevated CO(2). In contrast, aphid infested dnf1 plants had decreased activities of N assimilation-related enzymes and transmination-related enzymes and amino acid concentrations under elevated CO(2). Furthermore, elevated CO(2) up-regulated expression of genes relevant to amino acid metabolism in bacteriocytes of aphids associated with Jemalong, but down-regulated those associated with dnf1. Our results suggest that pea aphids actively elicit host responses that promote amino acid metabolism in both the host plant and in its bacteriocytes to favor the population growth of the aphid under elevated CO(2).
authors.affiliation: State Key Laboratory of Integrated Management of Pest and Rodents, Institute of Zoology, Chinese Academy of Sciences, Beijing, 100101, China; Graduate School, Chinese Academy of Sciences, Beijing, 100039, China.
authors.forename: Huijuan
authors.initials: H
authors.lastname: Guo
authors.forename: Yucheng
authors.initials: Y
authors.lastname: Sun
authors.forename: Yuefei
authors.initials: Y
authors.lastname: Li
authors.forename: Bin
authors.initials: B
authors.lastname: Tong
authors.forename: Marvin
authors.initials: M
authors.lastname: Harris
authors.forename: Keyan
authors.initials: K
authors.lastname: Zhu-Salzman
authors.forename: Feng
authors.initials: F
authors.lastname: Ge
mesh_terms: D000596:Amino Acids / Q000378:metabolism*; D000818:Animals; D001042:Aphids / Q000502:physiology*; D020635:Buchnera / Q000502:physiology; D002245:Carbon Dioxide / Q000502:physiology*; D005247:Feeding Behavior; D006790:Host-Parasite Interactions; D046913:Medicago truncatula / Q000469:parasitology / Q000502:physiology*; D011156:Population Density
chemical_list: D000596:Amino Acids; D002245:Carbon Dioxide
keywords: Acyrthosiphon pisum; Medicago truncatula; amino acid; bacteriocyte; biological nitrogen fixation; elevated CO2