title: Identification of Bradyrhizobium elkanii Genes Involved in Incompatibility with Soybean Plants Carrying the Rj4 Allele.
abstract: Symbioses between leguminous plants and soil bacteria known as rhizobia are of great importance to agricultural production and nitrogen cycling. While these mutualistic symbioses can involve a wide range of rhizobia, some legumes exhibit incompatibility with specific strains, resulting in ineffective nodulation. The formation of nodules in soybean plants (Glycine max) is controlled by several host genes, which are referred to as Rj genes. The soybean cultivar BARC2 carries the Rj4 gene, which restricts nodulation by specific strains, including Bradyrhizobium elkanii USDA61. Here we employed transposon mutagenesis to identify the genetic locus in USDA61 that determines incompatibility with soybean varieties carrying the Rj4 allele. Introduction of the Tn5 transposon into USDA61 resulted in the formation of nitrogen fixation nodules on the roots of soybean cultivar BARC2 (Rj4 Rj4). Sequencing analysis of the sequence flanking the Tn5 insertion revealed that six genes encoding a putative histidine kinase, transcriptional regulator, DNA-binding transcriptional activator, helix-turn-helix-type transcriptional regulator, phage shock protein, and cysteine protease were disrupted. The cysteine protease mutant had a high degree of similarity with the type 3 effector protein XopD of Xanthomonas campestris. Our findings shed light on the diverse and complicated mechanisms that underlie these highly host-specific interactions and indicate the involvement of a type 3 effector in Rj4 nodulation restriction, suggesting that Rj4 incompatibility is partly mediated by effector-triggered immunity.
authors.affiliation: Graduate School of Agriculture, Tokyo University of Agriculture and Technology, Tokyo, Japan.
authors.forename: Omar M
authors.initials: OM
authors.lastname: Faruque
authors.affiliation: Graduate School of Agriculture, Tokyo University of Agriculture and Technology, Tokyo, Japan.
authors.forename: Hiroki
authors.initials: H
authors.lastname: Miwa
authors.affiliation: Graduate School of Agriculture, Tokyo University of Agriculture and Technology, Tokyo, Japan.
authors.forename: Michiko
authors.initials: M
authors.lastname: Yasuda
authors.affiliation: Graduate School of Agriculture, Tokyo University of Agriculture and Technology, Tokyo, Japan.
authors.forename: Yoshiharu
authors.initials: Y
authors.lastname: Fujii
authors.affiliation: Faculty of Life Sciences, Kyoto Sangyo University, Kyoto, Japan.
authors.forename: Takakazu
authors.initials: T
authors.lastname: Kaneko
authors.affiliation: Graduate School of Life Sciences, Tohoku University, Sendai, Japan.
authors.forename: Shusei
authors.initials: S
authors.lastname: Sato
authors.affiliation: Graduate School of Agriculture, Tokyo University of Agriculture and Technology, Tokyo, Japan sokazaki@cc.tuat.ac.jp.
authors.forename: Shin
authors.identifier: http://orcid.org/0000-0002-6406-720X
authors.initials: S
authors.lastname: Okazaki
mesh_terms: D000483:Alleles; D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism; D020369:Bradyrhizobium / Q000235:genetics* / Q000502:physiology; D015964:Gene Expression Regulation, Bacterial; D008969:Molecular Sequence Data; D010940:Plant Proteins / Q000235:genetics* / Q000378:metabolism; D018517:Plant Roots / Q000235:genetics / Q000378:metabolism / Q000382:microbiology*; D013025:Glycine max / Q000235:genetics* / Q000382:microbiology / Q000502:physiology; D013559:Symbiosis
chemical_list: D001426:Bacterial Proteins; D010940:Plant Proteins