title: A Sinorhizobium meliloti osmosensory two-component system required for cyclic glucan export and symbiosis.
abstract: screen for novel symbiotic mutants of the nitrogen-fixing legume symbiont Sinorhizobium meliloti uncovered a crucial role for the putative response regulator FeuP in the symbiotic infection process. Transcriptome analysis shows that FeuP controls the transcription of at least 16 genes, including ndvA, which encodes an ATP-dependent exporter of cyclic beta glucans. Loss of feuP function gives rise to traits associated with cyclic beta glucan biosynthetic defects, including poor growth and motility under hypoosmotic conditions, and the inability to invade plant tissue during the early stages of symbiotic infection. Analysis of cyclic glucans indicates that the feuP mutant is able to synthesize intracellular cyclic beta glucans, but is unable to export them. Cyclic beta glucan export can be restored to feuP mutant cells by constitutive expression of ndvA; likewise, the symbiotic phenotype of a feuP mutant is rescued by ectopic ndvA expression. We further show that the linked sensor kinase gene, feuQ, is also important for modulating ndvA transcription, and that signalling through the FeuP/FeuQ pathway is responsive to extracellular osmotic conditions, with low osmolarity stimulating ndvA expression.
authors.affiliation: Department of Microbiology and Molecular Biology, Brigham Young University, Provo, UT 84602, USA. joelg@byu.edu
authors.forename: Joel S
authors.initials: JS
authors.lastname: Griffitts
authors.forename: Rebecca E
authors.initials: RE
authors.lastname: Carlyon
authors.forename: Jacob H
authors.initials: JH
authors.lastname: Erickson
authors.forename: Jason L
authors.initials: JL
authors.lastname: Moulton
authors.forename: Melanie J
authors.initials: MJ
authors.lastname: Barnett
authors.forename: Carol J
authors.initials: CJ
authors.lastname: Toman
authors.forename: Sharon R
authors.initials: SR
authors.lastname: Long
mesh_terms: D018528:ATP-Binding Cassette Transporters / Q000096:biosynthesis; D019677:Artificial Gene Fusion; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D001483:Base Sequence; D020869:Gene Expression Profiling; D023061:Gene Order; D017930:Genes, Reporter; D008124:Locomotion; D000455:Medicago sativa / Q000382:microbiology; D008969:Molecular Sequence Data; D009997:Osmotic Pressure; D015398:Signal Transduction; D016962:Sinorhizobium meliloti / Q000502:physiology*; D013559:Symbiosis; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D001616:beta-Galactosidase / Q000096:biosynthesis / Q000235:genetics; D047071:beta-Glucans / Q000378:metabolism*
chemical_list: D018528:ATP-Binding Cassette Transporters; D001426:Bacterial Proteins; C104567:FeuP protein, bacteria; C104568:FeuQ protein, bacteria; D014157:Transcription Factors; D047071:beta-Glucans; D001616:beta-Galactosidase