1 Temasek Life Sciences Laboratory, 1 Research Link, National University of Singapore, Singapore 117604, Republic of Singapore; and.
2 Department of Biological Sciences, 14 Science Drive, National University of Singapore, Singapore 117543, Republic of Singapore.
Mol Plant Microbe Interact. 2017 Jun;30(6):466-477. doi: 10.1094/MPMI-11-16-0229-R. Epub 2017 Apr 25.
Bacterial blight of rice, caused by Xanthomonas oryzae pv. oryzae, is one of the most destructive bacterial diseases throughout the major rice-growing regions in the world. The rice disease resistance (R) gene Xa10 confers race-specific disease resistance to X. oryzae pv. oryzae strains that deliver the corresponding transcription activator-like (TAL) effector AvrXa10. Upon bacterial infection, AvrXa10 binds specifically to the effector binding element in the promoter of the R gene and activates its expression. Xa10 encodes an executor R protein that triggers hypersensitive response and activates disease resistance. 'Nipponbare' rice carries two Xa10-like genes in its genome, of which one is the susceptible allele of the Xa23 gene, a Xa10-like TAL effector-dependent executor R gene isolated recently from 'CBB23' rice. However, the function of the two Xa10-like genes in disease resistance to X. oryzae pv. oryzae strains has not been investigated. Here, we designated the two Xa10-like genes as Xa10-Ni and Xa23-Ni and characterized their function for disease resistance to rice bacterial blight. Both Xa10-Ni and Xa23-Ni provided disease resistance to X. oryzae pv. oryzae strains that deliver the matching artificially designed TAL effectors (dTALE). Transgenic rice plants containing Xa10-Ni and Xa23-Ni under the Xa10 promoter provided specific disease resistance to X. oryzae pv. oryzae strains that deliver AvrXa10. Xa10-Ni and Xa23-Ni knock-out mutants abolished dTALE-dependent disease resistance to X. oryzae pv. oryzae. Heterologous expression of Xa10-Ni and Xa23-Ni in Nicotiana benthamiana triggered cell death. The 19-amino-acid residues at the N-terminal regions of XA10 or XA10-Ni are dispensable for their function in inducing cell death in N. benthamiana and the C-terminal regions of XA10, XA10-Ni, and XA23-Ni are interchangeable among each other without affecting their function. Like XA10, both XA10-Ni and XA23-Ni locate to the endoplasmic reticulum (ER) membrane, show self-interaction, and induce ER Ca depletion in leaf cells of N. benthamiana. The results indicate that Xa10-Ni and Xa23-Ni in Nipponbare encode functional executor R proteins, which induce cell death in both monocotyledonous and dicotyledonous plants and have the potential of being engineered to provide broad-spectrum disease resistance to plant-pathogenic Xanthomonas spp.
水稻细菌性条斑病由稻黄单胞菌引起，是世界主要水稻种植区最具破坏性的细菌性病害之一。水稻抗病（R）基因 Xa10 赋予水稻对携带相应转录激活样（TAL）效应物 AvrXa10 的稻黄单胞菌 pv.oryzae 菌株的特异性疾病抗性。在细菌感染时，AvrXa10 特异性地结合到 R 基因启动子中的效应物结合元件上，并激活其表达。Xa10 编码一种执行者 R 蛋白，可触发过敏反应并激活抗病性。“日本晴”水稻基因组中有两个 Xa10 样基因，其中一个是 Xa23 基因的感病等位基因，Xa23 是最近从“CBB23”水稻中分离出来的 Xa10 样 TAL 效应物依赖性执行者 R 基因。然而，这两个 Xa10 样基因在水稻对稻黄单胞菌 pv.oryzae 菌株的抗病性中的功能尚未得到研究。在这里，我们将这两个 Xa10 样基因命名为 Xa10-Ni 和 Xa23-Ni，并对它们在水稻细菌性条斑病中的抗病功能进行了表征。Xa10-Ni 和 Xa23-Ni 均为含有匹配人工设计的 TAL 效应物（dTALE）的稻黄单胞菌 pv.oryzae 菌株提供了抗病性。含有 Xa10 启动子下的 Xa10-Ni 和 Xa23-Ni 的转基因水稻植株对携带 AvrXa10 的稻黄单胞菌 pv.oryzae 菌株具有特异性的抗病性。Xa10-Ni 和 Xa23-Ni 的敲除突变体消除了对稻黄单胞菌 pv.oryzae 菌株的 dTALE 依赖性抗病性。Xa10-Ni 和 Xa23-Ni 在本氏烟中的异源表达引发了细胞死亡。XA10 或 XA10-Ni 的 N 端 19 个氨基酸残基对于其在诱导 N. benthamiana 细胞死亡中的功能是可有可无的，XA10、XA10-Ni 和 XA23-Ni 的 C 端区域在彼此之间是可互换的，而不会影响其功能。与 XA10 一样，XA10-Ni 和 XA23-Ni 都定位在内质网（ER）膜上，在本氏烟叶片细胞中表现出自相互作用，并诱导 ER Ca 耗竭。结果表明，日本晴中的 Xa10-Ni 和 Xa23-Ni 编码功能性执行者 R 蛋白，可诱导单子叶和双子叶植物的细胞死亡，并具有被工程改造以提供对植物病原黄单胞菌属广谱抗病性的潜力。
