title: The Sinorhizobium (Ensifer) fredii HH103 Nodulation Outer Protein NopI Is a Determinant for Efficient Nodulation of Soybean and Cowpea Plants.
abstract: The type III secretion system (T3SS) is a specialized secretion apparatus that is commonly used by many plant and animal pathogenic bacteria to deliver proteins, termed effectors, to the interior of the host cells. These effectors suppress host defenses and interfere with signal transduction pathways to promote infection. Some rhizobial strains possess a functional T3SS, which is involved in the suppression of host defense responses, host range determination, and symbiotic efficiency. The analysis of the genome of the broad-host-range rhizobial strainSinorhizobium frediiHH103 identified eight genes that code for putative T3SS effectors. Three of these effectors, NopL, NopP, and NopI, areRhizobiumspecific. In this work, we demonstrate that NopI, whose amino acid sequence shows a certain similarity with NopP, is secreted through theS. frediiHH103 T3SS in response to flavonoids. We also determined that NopL can be considered an effector since it is directly secreted to the interior of the host cell as demonstrated by adenylate cyclase assays. Finally, the symbiotic phenotype of single, double, and triplenopI,nopL, andnopPmutants in soybean and cowpea was assayed, showing that NopI plays an important role in determining the number of nodules formed in both legumes and that the absence of both NopL and NopP is highly detrimental for symbiosis.IMPORTANCEThe paper is focused on threeRhizobium-specific T3SS effectors ofSinorhizobium frediiHH103, NopL, NopP, and NopI. We demonstrate thatS. frediiHH103 is able to secrete through the T3SS in response to flavonoids the nodulation outer protein NopI. Additionally, we determined that NopL can be considered an effector since it is secreted to the interior of the host cell as demonstrated by adenylate cyclase assays. Finally, nodulation assays of soybean and cowpea indicated that NopI is important for the determination of the number of nodules formed and that the absence of both NopL and NopP negatively affected nodulation.
authors.affiliation: Departamento de Microbiología, Facultad de Biología, Universidad de Sevilla, Seville, Spain.
authors.forename: Irene
authors.initials: I
authors.lastname: Jiménez-Guerrero
authors.affiliation: Departamento de Microbiología, Facultad de Biología, Universidad de Sevilla, Seville, Spain.
authors.forename: Francisco
authors.initials: F
authors.lastname: Pérez-Montaño
authors.affiliation: Centro Andaluz de Biología del Desarrollo, Universidad Pablo de Olavide, Consejo Superior de Investigaciones Científicas, Junta de Andalucía, Seville, Spain.
authors.forename: Carlos
authors.initials: C
authors.lastname: Medina
authors.affiliation: Departamento de Microbiología, Facultad de Biología, Universidad de Sevilla, Seville, Spain.
authors.forename: Francisco Javier
authors.initials: FJ
authors.lastname: Ollero
authors.affiliation: Departamento de Microbiología, Facultad de Biología, Universidad de Sevilla, Seville, Spain jlopez@us.es.
authors.forename: Francisco Javier
authors.initials: FJ
authors.lastname: López-Baena
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism / Q000494:pharmacology*; D007887:Fabaceae / Q000382:microbiology; D017353:Gene Deletion; D015964:Gene Expression Regulation, Bacterial; D005798:Genes, Bacterial; D010641:Phenotype; D055170:Plant Root Nodulation / Q000187:drug effects*; D018517:Plant Roots / Q000382:microbiology*; D012231:Rhizobium / Q000378:metabolism; D016415:Sequence Alignment; D042181:Sinorhizobium fredii / Q000235:genetics / Q000378:metabolism*; D013025:Glycine max / Q000382:microbiology*; D013045:Species Specificity; D013559:Symbiosis / Q000235:genetics / Q000502:physiology*; D000069296:Type III Secretion Systems / Q000187:drug effects; D000070658:Vigna / Q000382:microbiology*
chemical_list: D001426:Bacterial Proteins; C486629:NopL protein, Rhizobium; D000069296:Type III Secretion Systems
keywords: Sinorhizobium fredii; cowpea; effector; nodulation; soybean; symbiosis; type III secretion