title: Sinorhizobium meliloti differentiation during symbiosis with alfalfa: a transcriptomic dissection.
abstract: Sinorhizobium meliloti is a soil bacterium able to induce the formation of nodules on the root of specific legumes, including alfalfa (Medicago sativa). Bacteria colonize nodules through infection threads, invade the plant intracellularly, and ultimately differentiate into bacteroids capable of reducing atmospheric nitrogen to ammonia, which is directly assimilated by the plant. As a first step to describe global changes in gene expression of S. meliloti during the symbiotic process, we used whole genome microarrays to establish the transcriptome profile of bacteria from nodules induced by a bacterial mutant blocked at the infection stage and from wild-type nodules harvested at various timepoints after inoculation. Comparison of these profiles to those of cultured bacteria grown either to log or stationary phase as well as examination of a number of genes with known symbiotic transcription patterns allowed us to correlate global gene-expression patterns to three known steps of symbiotic bacteria bacteroid differentiation, i.e., invading bacteria inside infection threads, young differentiating bacteroids, and fully differentiated, nitrogen-fixing bacteroids. Finally, analysis of individual gene transcription profiles revealed a number of new potential symbiotic genes.
authors.affiliation: Laboratoire des Interactions Plantes-Microorganismes, UMR INRA-CNRS 441-2594, BP52627, 31326 Castanet-Tolosan, France.
authors.forename: Delphine
authors.initials: D
authors.lastname: Capela
authors.forename: Cédric
authors.initials: C
authors.lastname: Filipe
authors.forename: Christine
authors.initials: C
authors.lastname: Bobik
authors.forename: Jacques
authors.initials: J
authors.lastname: Batut
authors.forename: Claude
authors.initials: C
authors.lastname: Bruand
mesh_terms: D001426:Bacterial Proteins / Q000378:metabolism; D016000:Cluster Analysis; D020869:Gene Expression Profiling; D015964:Gene Expression Regulation, Bacterial / Q000235:genetics*; D000455:Medicago sativa / Q000382:microbiology*; D018517:Plant Roots; D016962:Sinorhizobium meliloti / Q000235:genetics* / Q000502:physiology*; D013559:Symbiosis; D014158:Transcription, Genetic / Q000235:genetics*
chemical_list: D001426:Bacterial Proteins