Dataset Information

Bradyrhizobium (Arachis) sp. strain NC92 contains two nodD genes involved in the repression of nodA and a nolA gene required for the efficient nodulation of host plants.

ABSTRACT: The common nodulation locus and closely linked nodulation genes of Bradyrhizobium (Arachis) sp. strain NC92 have been isolated on an 11.0-kb EcoRI restriction fragment. The nucleotide sequence of a 7.0-kb EcoRV-EcoRI subclone was determined and found to contain open reading frames (ORFs) homologous to the nodA, nodB, nodD1, nodD2, and nolA genes of Bradyrhizobium japonicum and Bradyrhizobium elkanii. Nodulation assays of nodD1, nodD2, or nolA deletion mutants on the host plants Macroptilium atropurpureum (siratro) and Vigna unguiculata (cowpea) indicate that nolA is required for efficient nodulation, as nolA mutants exhibit a 6-day nodulation delay and reduced nodule numbers. The nolA phenotype was complemented by providing the nolA ORF in trans, indicating that the phenotype is due to the lack of the nolA ORF. nodD1 mutants displayed a 2-day nodulation delay, whereas nodD2 strains were indistinguishable from the wild type. Translational nodA-lacZ, nodD1-lacZ, nodD2-lacZ, and nolA-lacZ fusions were created. Expression of the nodA-lacZ fusion was induced by the addition of peanut, cowpea, and siratro seed exudates and by the addition of the isoflavonoids genistein and daidzein. In a nodD1 or nodD2 background, basal expression of the nodA-lacZ fusion increased two- to threefold. The level of expression of the nodD2-lacZ and nolA-lacZ fusions was low in the wild type but increased in nodD1, nodD2, and nodD1 nodD2 backgrounds independently of the addition of the inducer genistein. nolA was required for increased expression of the nodD2-lacZ fusion. These data suggest that a common factor is involved in the regulation of nodD2 and nolA, and they are also consistent with a model of nod gene expression in Bradyrhizobium (Arachis) sp. strain NC92 in which negative regulation is mediated by the products of the nodD1 and nodD2 genes.

SUBMITTER: Gillette WK

PROVIDER: S-EPMC178009 | biostudies-other | 1996 May

REPOSITORIES: biostudies-other

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Bradyrhizobium (Arachis) sp. strain NC92 contains two nodD genes involved in the repression of nodA and a nolA gene required for the efficient nodulation of host plants.

Gillette W K WK Elkan G H GH

Journal of bacteriology 19960501 10

The common nodulation locus and closely linked nodulation genes of Bradyrhizobium (Arachis) sp. strain NC92 have been isolated on an 11.0-kb EcoRI restriction fragment. The nucleotide sequence of a 7.0-kb EcoRV-EcoRI subclone was determined and found to contain open reading frames (ORFs) homologous to the nodA, nodB, nodD1, nodD2, and nolA genes of Bradyrhizobium japonicum and Bradyrhizobium elkanii. Nodulation assays of nodD1, nodD2, or nolA deletion mutants on the host plants Macroptilium atro ...[more]

PMID: 8631662

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Project description: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 strain Sinorhizobium fredii HH103 identified eight genes that code for putative T3SS effectors. Three of these effectors, NopL, NopP, and NopI, are Rhizobium specific. In this work, we demonstrate that NopI, whose amino acid sequence shows a certain similarity with NopP, is secreted through the S. fredii HH103 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 triple nopI, nopL, and nopP mutants 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.IMPORTANCE The paper is focused on three Rhizobium-specific T3SS effectors of Sinorhizobium fredii HH103, NopL, NopP, and NopI. We demonstrate that S. fredii HH103 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.

Dataset Information

Bradyrhizobium (Arachis) sp. strain NC92 contains two nodD genes involved in the repression of nodA and a nolA gene required for the efficient nodulation of host plants.

Publications

Bradyrhizobium (Arachis) sp. strain NC92 contains two nodD genes involved in the repression of nodA and a nolA gene required for the efficient nodulation of host plants.

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