State Key Laboratory of Plant Cell and Chromosome Engineering, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Beijing, China.
PLoS Pathog. 2012;8(6):e1002752. doi: 10.1371/journal.ppat.1002752. Epub 2012 Jun 7.
Plant intracellular immune receptors comprise a large number of multi-domain proteins resembling animal NOD-like receptors (NLRs). Plant NLRs typically recognize isolate-specific pathogen-derived effectors, encoded by avirulence (AVR) genes, and trigger defense responses often associated with localized host cell death. The barley MLA gene is polymorphic in nature and encodes NLRs of the coiled-coil (CC)-NB-LRR type that each detects a cognate isolate-specific effector of the barley powdery mildew fungus. We report the systematic analyses of MLA10 activity in disease resistance and cell death signaling in barley and Nicotiana benthamiana. MLA10 CC domain-triggered cell death is regulated by highly conserved motifs in the CC and the NB-ARC domains and by the C-terminal LRR of the receptor. Enforced MLA10 subcellular localization, by tagging with a nuclear localization sequence (NLS) or a nuclear export sequence (NES), shows that MLA10 activity in cell death signaling is suppressed in the nucleus but enhanced in the cytoplasm. By contrast, nuclear localized MLA10 is sufficient to mediate disease resistance against powdery mildew fungus. MLA10 retention in the cytoplasm was achieved through attachment of a glucocorticoid receptor hormone-binding domain (GR), by which we reinforced the role of cytoplasmic MLA10 in cell death signaling. Together with our data showing an essential and sufficient nuclear MLA10 activity in disease resistance, this suggests a bifurcation of MLA10-triggered cell death and disease resistance signaling in a compartment-dependent manner.
植物细胞内免疫受体包含大量类似于动物 NOD 样受体 (NLR) 的多结构域蛋白。植物 NLR 通常识别由无毒 (AVR) 基因编码的、具有特异性的病原体效应物，并引发常伴有局部宿主细胞死亡的防御反应。大麦 MLA 基因在本质上是多态的，它编码卷曲螺旋 (CC)-NB-LRR 型 NLR，每个 NLR 都能检测到大麦白粉菌的同源、具有特异性的效应物。我们报告了大麦和黄花烟（Nicotiana benthamiana）中 MLA10 在抗病性和细胞死亡信号转导中的系统分析。MLA10 CC 结构域触发的细胞死亡受到 CC 和 NB-ARC 结构域中的高度保守基序以及受体 C 末端 LRR 的调控。通过标记核定位序列（NLS）或核输出序列（NES）来强制 MLA10 亚细胞定位，表明 MLA10 在细胞死亡信号转导中的活性在细胞核中受到抑制，而在细胞质中增强。相比之下，核定位的 MLA10 足以介导对白粉菌的抗病性。通过附着糖皮质激素受体激素结合结构域 (GR) 实现 MLA10 在细胞质中的保留，我们强化了细胞质中 MLA10 在细胞死亡信号转导中的作用。结合我们的数据表明 MLA10 在抗病性中具有核必需和充分的活性，这表明 MLA10 触发的细胞死亡和抗病性信号转导以依赖区室的方式分叉。
