title: Different levels of transcriptional regulation due to trophic constraints in the reduced genome of Buchnera aphidicola APS.
abstract: Symbiotic associations involving intracellular microorganisms and animals are widespread, especially for species feeding on poor or unbalanced diets. Buchnera aphidicola, the obligate intracellular bacterium associated with most aphid species, provides its hosts with essential amino acids (EAAs), nutrients in short supply in the plant phloem sap. The Buchnera genome has undergone severe reductions during intracellular evolution. Genes for EAA biosynthesis are conserved, but most of the transcriptional regulatory elements are lost. This work addresses two main questions: is transcription in Buchnera (i) regulated and (ii) scaled to aphid EAA demand? Two microarray experiments were designed for profiling the gene expression in Buchnera. The first one was characterized by a specific depletion of tyrosine and phenylalanine in the aphid diet, and the second experiment combined a global diminution of EAAs in the aphid diet with a sucrose concentration increase to manipulate the aphid growth rate. Aphid biological performance and budget analysis (the balance between EAAs provided by the diet and those synthesized by Buchnera) were performed to quantify the nutritional demand from the aphids toward their symbiotic bacteria. Despite the absence of known regulatory elements, a significant transcriptional regulation was observed at different levels of organization in the Buchnera genome: between genes, within putative transcription units, and within specific metabolic pathways. However, unambiguous evidence for transcriptional changes underpinning the scaling of EAA biosynthesis to aphid demand was not obtained. The phenotypic relevance of the transcriptional response from the reduced genome of Buchnera is addressed.
authors.affiliation: UMR 203 INRA/INSA de Lyon, Biologie Fonctionnelle Insectes et Interactions (BF2I), INSA, Bât. Louis Pasteur, 69621 Villeurbanne Cedex, France.
authors.forename: Nancie
authors.initials: N
authors.lastname: Reymond
authors.forename: Federica
authors.initials: F
authors.lastname: Calevro
authors.forename: José
authors.initials: J
authors.lastname: Viñuelas
authors.forename: Nicolas
authors.initials: N
authors.lastname: Morin
authors.forename: Yvan
authors.initials: Y
authors.lastname: Rahbé
authors.forename: Gérard
authors.initials: G
authors.lastname: Febvay
authors.forename: Christian
authors.initials: C
authors.lastname: Laugier
authors.forename: Angela
authors.initials: A
authors.lastname: Douglas
authors.forename: Jean-Michel
authors.initials: JM
authors.lastname: Fayard
authors.forename: Hubert
authors.initials: H
authors.lastname: Charles
mesh_terms: D000601:Amino Acids, Essential / Q000378:metabolism; D000818:Animals; D001042:Aphids / Q000254:growth & development / Q000378:metabolism / Q000382:microbiology*; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D020635:Buchnera / Q000235:genetics / Q000378:metabolism*; D020869:Gene Expression Profiling; D015964:Gene Expression Regulation, Bacterial; D016680:Genome, Bacterial; D020411:Oligonucleotide Array Sequence Analysis; D013395:Sucrose / Q000378:metabolism; D013559:Symbiosis; D014158:Transcription, Genetic
chemical_list: D000601:Amino Acids, Essential; D001426:Bacterial Proteins; D013395:Sucrose