title: TtsI regulates symbiotic genes in Rhizobium species NGR234 by binding to tts boxes.
abstract: Infection of legumes by Rhizobium sp. NGR234 and subsequent development of nitrogen-fixing nodules are dependent on the coordinated actions of Nod factors, proteins secreted by a type III secretion system (T3SS) and modifications to surface polysaccharides. The production of these signal molecules is dependent on plant flavonoids which trigger a regulatory cascade controlled by the transcriptional activators NodD1, NodD2, SyrM2 and TtsI. TtsI is known to control the genes responsible for T3SS function and synthesis of a symbiotically important rhamnose-rich lipo-polysaccharide, most probably by binding to cis elements termed tts boxes. Eleven tts boxes were identified in the promoter regions of target genes on the symbiotic plasmid of NGR234. Expression profiles of lacZ fusions to these tts boxes showed that they are part of a TtsI-dependent regulon induced by plant-derived flavonoids. TtsI was purified and demonstrated to bind directly to two of these tts boxes. DNase I footprinting revealed that TtsI occupied not only the tts box consensus sequence, but also upstream and downstream regions in a concentration-dependent manner. Highly conserved bases of the consensus tts box were mutated and, although TtsI binding was still observed in vitro, gfp fusions were no longer transcribed in vivo. Random mutagenesis of a tts box-containing promoter revealed more nucleotides critical for transcriptional activity outside of the consensus.
authors: Laboratoire de Biologie Moléculaire des Plantes Supérieures, Sciences III, 30 Quai Ernest-Ansermet, Université de Genève, CH-1211 Geneva 4, Switzerland.
authors: Roseli
authors: R
authors: Wassem
authors: Hajime
authors: H
authors: Kobayashi
authors: Kumiko
authors: K
authors: Kambara
authors: Antoine
authors: A
authors: Le Quéré
authors: Graham C
authors: GC
authors: Walker
authors: William J
authors: WJ
authors: Broughton
authors: William J
authors: WJ
authors: Deakin
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism; D001483:Base Sequence; D016384:Consensus Sequence; D018983:DNA Footprinting; D024202:Electrophoretic Mobility Shift Assay; D015964:Gene Expression Regulation, Bacterial; D005798:Genes, Bacterial; D017930:Genes, Reporter; D008969:Molecular Sequence Data; D011401:Promoter Regions, Genetic; D020218:Response Elements; D012231:Rhizobium / Q000235:genetics* / Q000502:physiology; D017384:Sequence Deletion; D013559:Symbiosis; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic
chemical_list: D001426:Bacterial Proteins; D015534:Trans-Activators