1 Noble Research Institute, LLC, Ardmore, OK 73401, U.S.A.
2 Faculty of Life and Environmental Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8572, Japan.
Mol Plant Microbe Interact. 2017 Oct;30(10):829-841. doi: 10.1094/MPMI-03-17-0055-R. Epub 2017 Aug 22.
Chloroplasts have a crucial role in plant immunity against pathogens. Increasing evidence suggests that phytopathogens target chloroplast homeostasis as a pathogenicity mechanism. In order to regulate the performance of chloroplasts under stress conditions, chloroplasts produce retrograde signals to alter nuclear gene expression. Many signals for the chloroplast retrograde pathway have been identified, including chlorophyll intermediates, reactive oxygen species, and metabolic retrograde signals. Although there is a reasonably good understanding of chloroplast retrograde signaling in plant immunity, some signals are not well-understood. In order to understand the role of chloroplast retrograde signaling in plant immunity, we investigated Arabidopsis chloroplast retrograde signaling mutants in response to pathogen inoculation. sal1 mutants (fry1-2 and alx8) responsible for the SAL1-PAP retrograde signaling pathway showed enhanced disease symptoms not only to the hemibiotrophic pathogen Pseudomonas syringae pv. tomato DC3000 but, also, to the necrotrophic pathogen Pectobacterium carotovorum subsp. carotovorum EC1. Glucosinolate profiles demonstrated the reduced accumulation of aliphatic glucosinolates in the fry1-2 and alx8 mutants compared with the wild-type Col-0 in response to DC3000 infection. In addition, quantification of multiple phytohormones and analyses of their gene expression profiles revealed that both the salicylic acid (SA)- and jasmonic acid (JA)-mediated signaling pathways were down-regulated in the fry1-2 and alx8 mutants. These results suggest that the SAL1-PAP chloroplast retrograde pathway is involved in plant immunity by regulating the SA- and JA-mediated signaling pathways.
叶绿体在植物抵御病原体的免疫中起着至关重要的作用。越来越多的证据表明，植物病原体将叶绿体的内稳态作为一种致病性机制作为靶标。为了调节叶绿体在胁迫条件下的性能，叶绿体产生逆行信号以改变核基因表达。已经鉴定出许多叶绿体逆行途径的信号，包括叶绿素中间体、活性氧物种和代谢逆行信号。尽管人们对植物免疫中的叶绿体逆行信号有了相当好的理解，但有些信号还不太清楚。为了了解叶绿体逆行信号在植物免疫中的作用，我们研究了拟南芥叶绿体逆行信号突变体对病原体接种的反应。负责 SAL1-PAP 逆行信号通路的 sal1 突变体（fry1-2 和 alx8）不仅对半生物病原体丁香假单胞菌 pv.番茄 DC3000，而且对坏死病原体果胶杆菌亚种 carotovorum EC1 的疾病症状也有所增强。葡萄糖苷酸图谱表明，与野生型 Col-0 相比，fry1-2 和 alx8 突变体在受到 DC3000 感染时，脂肪族葡萄糖苷酸的积累减少。此外，多种植物激素的定量分析及其基因表达谱分析表明，在 fry1-2 和 alx8 突变体中，水杨酸（SA）和茉莉酸（JA）介导的信号通路都被下调。这些结果表明，SAL1-PAP 叶绿体逆行途径通过调节 SA 和 JA 介导的信号通路参与植物免疫。
