UMR Interactions Plantes-Microorganismes-Environnement, IRD-Cirad-UM, Montpellier, France.
INRA, Biology and Genetics of Plant-Pathogen Interactions Laboratory, Montpellier, France.
Plant J. 2016 Oct;88(1):43-55. doi: 10.1111/tpj.13231. Epub 2016 Aug 18.
Bacterial blight (BB) and bacterial leaf streak (BLS) are important diseases in Oryza sativa caused by Xanthomonas oryzae pv. oryzae (Xoo) and Xanthomonas oryzae pv. oryzicola (Xoc), respectively. In both bacteria, transcription activator-like (TAL) effectors are major virulence determinants that act by transactivating host genes downstream of effector-binding elements (EBEs) bound in a sequence-specific manner. Resistance to Xoo is mostly related to the action of TAL effectors, either by polymorphisms that prevent the induction of susceptibility (S) genes or by executor (R) genes with EBEs embedded in their promoter, and that induce cell death and resistance. For Xoc, no resistance sources are known in rice. Here, we investigated whether the recognition of effectors by nucleotide binding and leucine-rich repeat domain immune receptors (NLRs), the most widespread resistance mechanism in plants, is also able to stop BB and BLS. In one instance, transgenic rice lines harboring the AVR1-CO39 effector gene from the rice blast fungus Magnaporthe oryzae, under the control of an inducible promoter, were challenged with transgenic Xoo and Xoc strains carrying a TAL effector designed to transactivate the inducible promoter. This induced AVR1-CO39 expression and triggered BB and BLS resistance when the corresponding Pi-CO39 resistance locus was present. In a second example, the transactivation of an auto-active NLR by Xoo-delivered designer TAL effectors resulted in BB resistance, demonstrating that NLR-triggered immune responses efficiently control Xoo. This forms the foundation for future BB and BLS disease control strategies, whereupon endogenous TAL effectors will target synthetic promoter regions of Avr or NLR executor genes.
细菌性条斑病（BB）和细菌性褐条病（BLS）是由稻黄单胞菌（Xoo）和稻黄单胞菌（Xoc）引起的重要水稻病害。在这两种细菌中，转录激活子样（TAL）效应子是主要的毒力决定因素，通过顺式激活效应子结合元件（EBE）下游的宿主基因来发挥作用，EBE 以序列特异性的方式结合。Xoo 的抗性主要与 TAL 效应子的作用有关，要么是通过阻止易感性（S）基因诱导的多态性，要么是通过在启动子中嵌入 EBE 的执行者（R）基因，从而诱导细胞死亡和抗性。对于 Xoc，在水稻中尚未发现抗性来源。在这里，我们研究了核苷酸结合和富含亮氨酸重复域免疫受体（NLRs）是否也能识别效应子，NLRs 是植物中最广泛的抗性机制。在一种情况下，含有稻瘟病菌 Magnaporthe oryzae 的 AVR1-CO39 效应子基因的转基因水稻品系，在诱导型启动子的控制下，受到携带设计用于激活诱导型启动子的 TAL 效应子的转基因 Xoo 和 Xoc 菌株的挑战。当存在相应的 Pi-CO39 抗性基因座时，这会诱导 AVR1-CO39 的表达，并引发 BB 和 BLS 抗性。在第二个例子中，Xoo 传递的设计 TAL 效应子对自主激活的 NLR 的转激活导致了 BB 抗性，这表明 NLR 触发的免疫反应有效地控制了 Xoo。这为未来的 BB 和 BLS 疾病控制策略奠定了基础，在该策略中，内源性 TAL 效应子将靶向 Avr 或 NLR 执行者基因的合成启动子区域。
