Most potato cultivars are susceptible to late blight disease caused by the oomycete pathogen Phytophthora infestans. A new source of resistance to prevent or diminish pathogen infection is found in the genetic loss of host susceptibility. Previously, we showed that RNAi-mediated silencing of the potato susceptibility (S) genes StDND1, StDMR1 and StDMR6 leads to increased late blight resistance. The mechanisms underlying this S-gene mediated resistance have thus far not been identified. In this study, we examined the infection process of P. infestans on StDND1-, StDMR1- and StDMR6-silenced potato lines. Microscopic analysis showed that penetration of P. infestans spores was hampered on StDND1-silenced plants. On StDMR1- and StDMR6-silenced plants, P. infestans infection was arrested at a primary infection stage by enhanced cell death responses. Histochemical staining revealed that StDMR1- and StDMR6-silenced plants display elevated ROS levels in cells at the infection sites. Resistance in StDND1-silenced plants, however, seems not to rely on a cell death response as ROS accumulation was found to be absent at most inoculated sites. Quantitative analysis of marker gene expression suggests that the increased resistance observed in StDND1- and StDMR6-silenced plants relies on an early onset of SA- and ET-mediated signalling pathways. Resistance mediated by silencing StDMR1 was found to be correlated with the early induction of SA-mediated signalling. These data provide evidence that different defense mechanisms are involved in late blight resistance mediated by functional impairment of different potato S-genes.

中文翻译：

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沉默马铃薯易感基因可阻碍马铃薯晚疫病菌在不同阶段的初侵染。


大多数马铃薯品种易受卵菌病原体致病疫霉（Phytophthora infestans）引起的晚疫病的影响。宿主易感性的遗传丧失中发现了预防或减少病原体感染的新抵抗力来源。此前，我们发现 RNAi 介导的马铃薯易感基因 StDND1、StDMR1 和 StDMR6 沉默可导致晚疫病抗性增强。迄今为止，尚未确定这种 S 基因介导的耐药性的潜在机制。在本研究中，我们检测了致病疫霉对 StDND1、StDMR1 和 StDMR6 沉默马铃薯品系的感染过程。显微镜分析表明，致病疫霉孢子的渗透在 StDND1 沉默的植物上受到阻碍。在 StDMR1 和 StDMR6 沉默的植物上，致病疫霉感染通过增强的细胞死亡反应在初级感染阶段被阻止。组织化学染色显示，StDMR1 和 StDMR6 沉默的植物在感染部位的细胞中表现出升高的 ROS 水平。然而，StDND1 沉默植物的抗性似乎并不依赖于细胞死亡反应，因为发现大多数接种位点不存在 ROS 积累。标记基因表达的定量分析表明，在 StDND1 和 StDMR6 沉默植物中观察到的抗性增加依赖于 SA 和 ET 介导的信号通路的早期启动。研究发现，通过沉默 StDMR1 介导的耐药性与 SA 介导的信号传导的早期诱导相关。这些数据提供了证据表明不同的防御机制参与了由不同马铃薯S基因功能损伤介导的晚疫病抗性。