Identification of Bradyrhizobium elkanii Genes Involved in Incompatibility with Soybean Plants Carrying the Rj4 Allele
Identification of Bradyrhizobium elkanii Genes Involved in Incompatibility with Soybean Plants Carrying the Rj4 Allele
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DOI：
10.1128/aem.01942-15
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发表时间：
2015-10-01
影响因子：
4.4
通讯作者：
Okazaki, Shin
中科院分区：
文献类型：
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作者：
Faruque, Omar M.;Miwa, Hiroki;Okazaki, Shin
豆科植物与土壤中的根瘤菌共生，对农业生产和氮素循环具有重要意义。虽然这些互惠共生可以涉及广泛的根瘤菌，但一些豆类植物表现出与特定菌株的不相容性，导致无效的共生。大豆（Glycine max）中根瘤的形成受几个宿主基因控制，这些宿主基因被称为Rj基因。大豆栽培品种BARC 2携带Rj 4基因，其限制特定菌株（包括埃氏慢生根瘤菌USDA 61）的发酵。在这里，我们采用转座子诱变来确定USDA 61中决定与携带Rj 4等位基因的大豆品种不亲和的遗传位点。将Tn 5转座子导入USDA 61导致在大豆栽培品种BARC 2（Rj 4 Rj 4）的根上形成固氮根瘤。Tn 5插入侧翼序列的测序分析显示，6个基因编码一个假定的组氨酸激酶，转录调节因子，DNA结合转录激活因子，螺旋-转角-螺旋型转录调节因子，噬菌体休克蛋白，和半胱氨酸蛋白酶被破坏。半胱氨酸蛋白酶突变体与野油菜黄单胞菌3型效应蛋白XopD具有高度的相似性。我们的研究结果揭示了这些高度宿主特异性相互作用的基础上的多样性和复杂的机制，并表明3型效应子参与Rj 4抑制限制，表明Rj 4不相容性部分由效应子触发的免疫介导。
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.