Mol Plant Microbe Interact. 2014 May;27(5):403-14. doi: 10.1094/MPMI-10-13-0317-R.
Programmed cell death is a key feature of epidermal plant immunity, which is particularly effective against biotrophic microbes that depend on living host tissue. The covered smut fungus Ustilago hordei establishes a compatible biotrophic interaction with its host plant barley. The maize smut U. maydis triggers a nonhost response in barley, which results in epidermal cell death. Similarly, Ustilago mutants being deleted for pep1, a gene encoding a secreted effector, are blocked upon host penetration. We studied the epidermal responses of barley to incompatible Ustilago strains. Molecular and cellular analyses were used to test the impact of Bax inhibitor-1 (BI-1), a suppressor of programmed cell death, on the barley nonhost resistance to U. maydis as well as Ustilago Δpep1 mutants. Overexpression of BI-1 resulted in partial break of barley nonhost resistance to U. maydis. By contrast, the epidermal cell death response triggered by pep1 deletion mutants was not impaired by BI-1. Hypersensitive-response-like cell death caused by U. maydis wild-type infection showed features of necrotic cell death, while Δpep1 mutant-induced host responses involved hallmarks of autophagy. Therefore, we propose that the mechanisms of epidermal cell death in response to different types of incompatible pathogens depend on spatial and temporal appearance of cell-death-triggering stimuli.
细胞程序性死亡是植物表皮免疫的一个关键特征，它对依赖于活体宿主组织的生物营养型微生物尤其有效。黑麦壳针孢菌 Ustilago hordei 与宿主大麦建立了一种兼容的生物营养型相互作用。玉米黑粉菌 U. maydis 在大麦中引发非宿主反应，导致表皮细胞死亡。同样，缺失编码分泌效应物 pep1 的基因的 Ustilago 突变体在穿透宿主时被阻断。我们研究了大麦对不亲和 Ustilago 菌株的表皮反应。分子和细胞分析用于测试 Bax 抑制剂-1 (BI-1) 对大麦非宿主对 U. maydis 以及 Ustilago Δpep1 突变体的抗性的影响，BI-1 是程序性细胞死亡的抑制剂。BI-1 的过表达导致大麦对 U. maydis 的非宿主抗性部分破坏。相比之下，BI-1 对 pep1 缺失突变体诱导的表皮细胞死亡反应没有影响。由 U. maydis 野生型感染引起的过敏反应样细胞死亡表现出坏死细胞死亡的特征，而 Δpep1 突变体诱导的宿主反应则涉及自噬的特征。因此，我们提出，对不同类型不亲和病原体的表皮细胞死亡的机制取决于细胞死亡触发刺激的时空出现。
