title: Bradyoxetin, a unique chemical signal involved in symbiotic gene regulation.
abstract: Bradyrhizobium japonicum is a symbiotic bacterium that nodulates soybean. Critical for the infection and establishment of this symbiosis are the bacterial nodulation genes (nod, nol, noe), which are induced in the presence of plant produced isoflavones. Transcription of the nodulation genes is also controlled in a population density-dependent fashion. Expression of the nod genes is maximal at low population densities, and decreases significantly at higher culture densities. Population density control of the nodulation genes involves NolA and NodD2, both of which function in tandem to repress nod gene expression. An extracellular secreted factor (CDF) is known to mediate this repression. Here, we report that CDF is a novel signaling molecule, designated bradyoxetin, different from other Gram-negative quorum signals. The proposed structure of bradyoxetin is 2-[4-[[4-(3-aminooxetan-2-yl)phenyl](imino)methyl]phenyl]oxetan-3-ylamine. Interestingly, expression of bradyoxetin is iron-regulated, and is maximally produced under iron-starved conditions. Consistent with this, expression of the nodulation genes occurred in an iron-dependent fashion. Addition of iron to B. japonicum cultures at high optical densities resulted in decreased bradyoxetin production, and a concomitant reduction in nolA expression. A corresponding increase in nodY-lacZ expression was observed with iron treatment.
authors.affiliation: Department of Plant Microbiology and Pathology, University of Missouri, Columbia, MO 65211, USA.
authors.forename: John
authors.initials: J
authors.lastname: Loh
authors.forename: Russell W
authors.initials: RW
authors.lastname: Carlson
authors.forename: William S
authors.initials: WS
authors.lastname: York
authors.forename: Gary
authors.initials: G
authors.lastname: Stacey
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics*; D020369:Bradyrhizobium / Q000235:genetics* / Q000378:metabolism; D004988:Ethers, Cyclic / Q000378:metabolism*; D005290:Ferric Compounds / Q000378:metabolism; D005786:Gene Expression Regulation; D007097:Imines / Q000378:metabolism*; D013025:Glycine max / Q000382:microbiology; D013559:Symbiosis; D014157:Transcription Factors
chemical_list: D001426:Bacterial Proteins; D004988:Ethers, Cyclic; D005290:Ferric Compounds; D007097:Imines; D014157:Transcription Factors; C468924:bradyoxetin; C066978:nolA protein, Bradyrhizobium