Belhaj Khaoula, Lin Baiqing, Mauch Felix
Department of Biology, University of Fribourg, Fribourg, Switzerland.
Plant J. 2009 Apr;58(2):287-98. doi: 10.1111/j.1365-313X.2008.03779.x. Epub 2008 Dec 16.
Plant immune responses to pathogens are often associated with enhanced production of reactive oxygen species (ROS), known as the oxidative burst, and with rapid hypersensitive host cell death (the hypersensitive response, HR) at sites of attempted infection. It is generally accepted that the oxidative burst acts as a promotive signal for HR, and that HR is highly correlated with efficient disease resistance. We have identified the Arabidopsis mutant rph1 (resistance to Phytophthora 1), which is susceptible to the oomycete pathogen Phytophthora brassicae despite rapid induction of HR. The susceptibility of rph1 was specific for P. brassicae and coincided with a reduced oxidative burst, a runaway cell-death response, and failure to properly activate the expression of defence-related genes. From these results, we conclude that, in the immune response to P. brassicae, (i) HR is not sufficient to stop the pathogen, (ii) HR initiation can occur in the absence of a major oxidative burst, (iii) the oxidative burst plays a role in limiting the spread of cell death, and (iv) RPH1 is a positive regulator of the P. brassicae-induced oxidative burst and enhanced expression of defence-related genes. Surprisingly, RPH1 encodes an evolutionary highly conserved chloroplast protein, indicating a function of this organelle in activation of a subset of immune reactions in response to P. brassicae. The disease resistance-related role of RPH1 was not limited to the Arabidopsis model system. Silencing of the potato homolog StRPH1 in a resistant potato cultivar caused susceptibility to the late blight pathogen Phytophthora infestans.
植物对病原体的免疫反应通常与活性氧（ROS）产量增加（即氧化爆发）以及在试图感染部位宿主细胞的快速超敏死亡（超敏反应，HR）有关。人们普遍认为氧化爆发作为HR的促进信号，并且HR与有效的抗病性高度相关。我们鉴定了拟南芥突变体rph1（对疫霉1的抗性），尽管其能快速诱导HR，但仍对卵菌病原体芸苔疫霉敏感。rph1的敏感性对芸苔疫霉具有特异性，且与氧化爆发减少、失控的细胞死亡反应以及未能正确激活防御相关基因的表达同时出现。从这些结果中，我们得出结论，在对芸苔疫霉的免疫反应中，（i）HR不足以阻止病原体，（ii）HR的启动可以在没有主要氧化爆发的情况下发生，（iii）氧化爆发在限制细胞死亡扩散中起作用，并且（iv）RPH1是芸苔疫霉诱导的氧化爆发和防御相关基因增强表达的正调节因子。令人惊讶地是，RPH1编码一种进化上高度保守的叶绿体蛋白，表明该细胞器在激活对芸苔疫霉的一部分免疫反应中具有功能。RPH1的抗病相关作用并不局限于拟南芥模型系统。在一个抗病马铃薯品种中沉默马铃薯同源物StRPH1会导致对晚疫病病原体致病疫霉敏感。
