高表达Nt-RDR1基因的植物，表现出对病毒的高度敏感（病毒荧光增强）。Nb为野生型植物对照。
RNA沉默途径（RNAi途径）和水杨酸抗性途径（SA途径）是植物抗病反应调控系统中两条非常重要的信号转导通路。植物中依赖于RNA的RNA聚合酶（RNA-dependent RNA polymerases, RDRs）家族有不同成员各自参与这两条抗性途径。其中，RDR6参与RNAi途径，扩增RNAi途径的关键因子小RNA（siRNA），并对抵抗病毒的侵染起关键的作用；而RDR1主要参与SA介导的抗病毒途径。
在一种本明烟（Nicotiana benthamiana）烟草中， RDR1被发现自然突变成无功能基因。以往假设认为：可能由于本明烟中与SA-途径相关的RDR1的突变，导致本明烟很容易被病毒感染，使其成为一种可被多种病毒寄生的植物宿主。
近日，中国科学院微生物研究所植物基因组学国家重点实验室郭惠珊研究组通过分析与本明烟RDR1高度同源的普通烟草（Nicotiana tabacum）的RDR1（Nt-RDR1），发现Nt-RDR1在本明烟中过表达，非但不能提高本明烟对病毒的抗性，反而使本明烟对很多病毒出现超感表型。他们进一步研究发现，Nt-RDR1蛋白具有RNA沉默抑制子活性。Nt-RDR1蛋白能抑制RDR6参与的RNAi途径，干扰依赖RDR6产生的siRNA的沉默活性。该研究提供证据表明：RDR1蛋白具有双功能作用，一方面，参与SA抗性途径，另一方面，抑制RDR6介导的抗病毒RNAi途径。
该项研究揭示了本明烟RDR1自然突变的生物学意义。阐明本明烟RDR1的自然突变可能是植物本身长期面临广泛病毒侵染的选择压力而发生的结果，通过RDR1的失活突变以激活更强的RDR6介导的抗病毒能力。该研究为植物抗病途径在农业抗病毒生产应用上提供了新的证据。研究论文已在线发表于2010年4月16日的《植物细胞》（The Plant Cell）上。（生物谷Bioon.com）
更多阅读
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植物信号传导研究取得重大进展
生物谷推荐原文出处：
Plant Cell doi：10.1105/tpc.109.072058
RNA-Dependent RNA Polymerase 1 from Nicotiana tabacum Suppresses RNA Silencing and Enhances Viral Infection in Nicotiana benthamiana
Xiao-Bao Yinga,b, Li Donga, Hui Zhua,b, Cheng-Guo Duana, Quan-Sheng Dua, Dian-Qiu Lva,c, Yuan-Yuan Fanga, Juan Antonio Garciad, Rong-Xiang Fanga and Hui-Shan Guoa,1
a State Key Laboratory of Plant Genomics and National Center for Plant Gene Research (Beijing), Institute of Microbiology, Chinese Academy of Sciences, Beijing, 100101, China
b Graduate University of Chinese Academy of Sciences, Beijing, 100049, China
c Virus-Free Seedling Institute of Heilongjiang Academy of Agricultural Sciences, Heilongjiang, 150086, Haerbin
d Department of Plant Molecular Genetics, Centro National de Biotecnologia (Consejo Superior de Investigaciones Científicas), Campus Universidad Autonoma de Madrid, 28049 Madrid, Spain
Endogenous eukaryotic RNA-dependent RNA polymerases (RDRs) produce double-stranded RNA intermediates in diverse processes of small RNA synthesis in RNA silencing pathways. RDR6 is required in plants for posttranscriptional gene silencing induced by sense transgenes (S-PTGS) and has an important role in amplification of antiviral silencing. Whereas RDR1 is also involved in antiviral defense in plants, this does not necessarily proceed through triggering silencing. In this study, we show that Nicotiana benthamiana transformed with RDR1 from Nicotiana tabacum (Nt-RDR1 plants) exhibits hypersusceptibility to Plum pox potyvirus and other viruses, resembling RDR6-silenced (RDR6i) N. benthamiana. Analysis of transient induction of RNA silencing in N. benthamiana Nt-RDR1 and RDR6i plants revealed that Nt-RDR1 possesses silencing suppression activity. We found that Nt-RDR1 does not interfere with RDR6-dependent siRNA accumulation but turns out to suppress RDR6-dependent S-PTGS. Our results, together with previously published data, suggest that RDR1 might have a dual role, contributing, on one hand, to salicylic acid–mediated antiviral defense, and suppressing, on the other hand, the RDR6-mediated antiviral RNA silencing. We propose a scenario in which the natural loss-of-function variant of RDR1 in N. benthamiana may be the outcome of selective pressure to maintain a high RDR6-dependent antiviral defense, which would be required to face the hypersensitivity of this plant to a large number of viruses.
