title: Selection of unusual actinomycetal primary sigma70 factors by plant-colonizing Frankia strains.
abstract: Functional adaptations of sigma70 transcriptional factors led to the emergence of several paralogous lineages, each one being specialized for gene transcription under particular growth conditions. Screening of a Frankia strain EaI-12 gene library by sigma70 DNA probing allowed the detection and characterization of a novel actinomycetal primary (housekeeping) sigma70 factor. Phylogenetic analysis positioned this factor in the RpoD cluster of proteobacterial and low-G+C-content gram-positive factors, a cluster previously free of any actinobacterial sequences. sigma70 DNA probing of Frankia total DNA blots and PCR screening detected one or two rpoD-like DNA regions per species. rpoD matched the conserved region in all of the species tested. The other region was found to contain sigA, an alternative primary factor. sigA appeared to be strictly distributed among Frankia species infecting plants by the root hair infection process. Both genes were transcribed by Frankia strain ACN14a grown in liquid cultures. The molecular phylogeny of the sigma70 family determined with Frankia sequences showed that the alternative actinomycetal factors and the essential ones belonged to the same radiation. At least seven distinct paralogous lineages were observed among this radiation, and gene transfers were detected in the HrdB actinomycetal lineage.
authors.affiliation: Research Group on Opportunistic Pathogens and the Environment, Ecologie Microbienne (Center for Microbial Ecology), UMR CNRS 5557-Université Claude Bernard-Lyon 1, USC INRA 1193, 69622 Villeurbanne Cedex, France.
authors.forename: Céline
authors.initials: C
authors.lastname: Lavire
authors.forename: Didier
authors.initials: D
authors.lastname: Blaha
authors.forename: Benoit
authors.initials: B
authors.lastname: Cournoyer
mesh_terms: D001483:Base Sequence; D012321:DNA-Directed RNA Polymerases / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D031263:Elaeagnaceae / Q000382:microbiology*; D040161:Frankia / Q000235:genetics* / Q000378:metabolism; D015964:Gene Expression Regulation, Bacterial; D008969:Molecular Sequence Data; D010802:Phylogeny; D010935:Plant Diseases / Q000382:microbiology*; D012641:Selection, Genetic; D017422:Sequence Analysis, DNA; D012808:Sigma Factor / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism
chemical_list: D012808:Sigma Factor; C081775:RNA polymerase sigma 70; D012321:DNA-Directed RNA Polymerases