Roles of flavonoids and the transcriptional regulator TtsI in the activation of the type III secretion system of Bradyrhizobium elkanii SEMIA587.
Bradyrhizobium elkanii SEMIA587 is a symbiotic nitrogen-fixing bacterium of the group commonly called rhizobia, which induce nodule formation in legumes, and is widely used in Brazilian commercial inoculants of soybean. In response to flavonoid compounds released by plant roots, besides Nod factors, other molecular signals are secreted by rhizobia, such as proteins secreted by type III secretion systems (T3SSs). Rhizobial T3SSs are activated by the transcription regulator TtsI, which binds to sequences present in the promoter regions of T3SS genes via a conserved sequence called the tts box. To study the role of the T3SS of B. elkanii SEMIA587, ttsI was mutated. Protein secretion and flavonoid induction analysis, as well as nodulation tests, were performed with the wild-type and mutant strains. The results obtained showed that B. elkanii SEMIA587 secretes at least two proteins (NopA and NopL, known rhizobial T3SS substrates) after genistein induction, whilst supernatants of the ttsI mutant did not contain these Nops. Unusually for rhizobia, the promoter region of the B. elkanii SEMIA587 ttsI gene contains a tts box, which is responsive to flavonoid induction and to which TtsI can bind. Nodulation tests performed with three different leguminous plants showed that the B. elkanii SEMIA587 ttsI mutant displays host-dependent characteristics; in particular, nodulation of two soybean cultivars, Peking and EMBRAPA 48, was more efficient when TtsI of B. elkanii was functional.
Universidade Federal do Rio Grande do Sul, Instituto de Biociências, Departamento de Genética, Av. Bento Gonçalves, 9500, Caixa Postal 15.053, CEP 91501-970, Porto Alegre, RS, Brazil.
Samanta
S
Bolzan de Campos
Laboratoire de Biologie Moléculaire des Plantes Supérieures (LBMPS), Département de Biologie Végétale, Sciences III, 30 Quai Ernest-Ansermet, University of Geneva, CH-1211 Geneva 4, Switzerland.
William J
WJ
Deakin
Laboratoire de Biologie Moléculaire des Plantes Supérieures (LBMPS), Département de Biologie Végétale, Sciences III, 30 Quai Ernest-Ansermet, University of Geneva, CH-1211 Geneva 4, Switzerland.
William J
WJ
Broughton
Universidade Federal do Rio Grande do Sul, Instituto de Biociências, Departamento de Genética, Av. Bento Gonçalves, 9500, Caixa Postal 15.053, CEP 91501-970, Porto Alegre, RS, Brazil.
Luciane M P
LMP
Passaglia
D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D058947:Bacterial Secretion Systems; D001483:Base Sequence; D020369:Bradyrhizobium / Q000187:drug effects* / Q000235:genetics / Q000254:growth & development / Q000378:metabolism; D017124:Conserved Sequence; D004742:Enhancer Elements, Genetic; D005419:Flavonoids / Q000378:metabolism / Q000494:pharmacology*; D015964:Gene Expression Regulation, Bacterial; D019833:Genistein / Q000378:metabolism / Q000494:pharmacology; D007529:Isoflavones / Q000378:metabolism / Q000494:pharmacology; D008969:Molecular Sequence Data; D009154:Mutation; D011401:Promoter Regions, Genetic; D017422:Sequence Analysis, DNA; D013025:Glycine max / Q000378:metabolism / Q000382:microbiology*; D013559:Symbiosis; D014157:Transcription Factors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
D001426:Bacterial Proteins; D058947:Bacterial Secretion Systems; D005419:Flavonoids; D007529:Isoflavones; D014157:Transcription Factors; C004742:daidzein; D019833:Genistein