title: The Sinorhizobium meliloti RNA chaperone Hfq mediates symbiosis of S. meliloti and alfalfa.
abstract: There exist commonalities between symbiotic Sinorhizobium meliloti and pathogenic Brucella bacteria in terms of extensive gene synteny and the requirements for intracellular survival in their respective hosts. The RNA chaperone Hfq is essential for virulence for several bacterial groups, including Brucella; however, its role in S. meliloti has not been investigated. Our studies of an S. meliloti loss-of-function hfq mutant have revealed that Hfq plays a key role in the establishment of the symbiosis between S. meliloti and its host Medicago sativa. S. meliloti Hfq is involved in controlling the population density under a free-living state and affects the growth parameters and nodulation. An hfq mutant poorly colonizes the infection threads that are necessary for the bacteria to invade the developing nodule. An hfq mutant is severely impaired in its ability to invade plant cells within the nodule, which leads to the formation of small, ineffective nodules unable to fix nitrogen. In culture, the hfq mutant did not accumulate transcripts of nifA, which encodes a key regulator necessary for nitrogen fixation. Hfq may be involved in regulation of several proteins relevant to hfq mutant phenotypes. The crucial role of Hfq in symbiosis suggests that small regulatory RNAs are important for its interactions with its plant host.
authors.affiliation: Department of Biology, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139-4307, USA.
authors.forename: Lise
authors.initials: L
authors.lastname: Barra-Bily
authors.forename: Shree P
authors.initials: SP
authors.lastname: Pandey
authors.forename: Annie
authors.initials: A
authors.lastname: Trautwetter
authors.forename: Carlos
authors.initials: C
authors.lastname: Blanco
authors.forename: Graham C
authors.initials: GC
authors.lastname: Walker
mesh_terms: D015964:Gene Expression Regulation, Bacterial / Q000502:physiology*; D035001:Host Factor 1 Protein / Q000235:genetics / Q000378:metabolism*; D000455:Medicago sativa / Q000382:microbiology*; D055170:Plant Root Nodulation; D018517:Plant Roots / Q000382:microbiology; D011135:Polysaccharides, Bacterial / Q000096:biosynthesis; D016962:Sinorhizobium meliloti / Q000235:genetics / Q000378:metabolism*; D013559:Symbiosis
chemical_list: D035001:Host Factor 1 Protein; D011135:Polysaccharides, Bacterial; C056779:succinoglycan