中文摘要：植物受到病原菌侵染时可通过过敏性反应引起水杨酸浓度升高，从而使植物获得更强的抵抗更多病原菌二次侵染的抗性。这个现象被称为系统获得性抗性（SAR），这是一种由植物自身启动用于适应重复的生物胁迫的抗性。然而，SAR介导的尤其是对病毒侵染的抑制性的分子机制仍是未知。本研究表明，抵抗黄瓜花叶病毒的增强的抗性是由烟草类钙调素蛋白，即rgs-CaM引起的，rgs-CaM在SAR诱导后可检测和抵抗主要的病毒毒力因子（RNA沉默抑制子）。
外文摘要：Primary infection of a plant with a pathogen that causes high accumulation of salicylic acid in the plant typically via a hypersensitive response confers enhanced resistance against secondary infection with a broad spectrum of pathogens, including viruses. This phenomenon is called systemic acquired resistance (SAR), which is a plant-priming for adaption to repeated biotic stress. However, the molecular mechanisms of SAR-mediated enhanced inhibition, especially of virus infection, remain unclear. Here, we show that SAR against cucumber mosaic virus (CMV) in tobacco plants ( Nicotiana tabacum ) involves a calmodulin-like protein, rgs-CaM. We previously reported the antiviral function of rgs-CaM, which binds to and directs degradation of viral RNA silencing suppressors (RSSs), including CMV 2b, via autophagy. We found that rgs-CaM-mediated immunity is ineffective against CMV infection in normally growing tobacco plants but is activated in SAR-induced plants via induction of salicylic acid signaling. We then analyzed the effect of overexpression of rgs-CaM on salicylic acid signaling. Overexpressed and ectopically expressed rgs-CaM induced defense reactions including cell death, generation of reactive oxygen species, and salicylic acid signaling. Further analysis using a combination of salicylic acid analogue BTH and Ca 2+ ionophore, A23187, revealed that rgs-CaM functions as an immune receptor that induces salicylic acid signaling by simultaneously perceives both viral RSS and Ca 2+ influx as infection cues, implying its autoactivation. Thus, secondary infection of SAR-induced tobacco plants with CMV seems to be effectively inhibited through 2b recognition and degradation by rgs-CaM, leading to reinforcement of antiviral RNA silencing and other salicylic acid-mediated antiviral responses. IMPORTANCE Even without an acquired immune system like that in vertebrates, plants show enhanced whole-plant resistance against secondary infection with pathogens; this so-called systemic acquired resistance (SAR) has been known for more than half a century and continues to be extensively studied. SAR-induced plants strongly and rapidly express a number of antibiotics and pathogenesis-related proteins targeted against secondary infection, which can account for enhanced resistance against bacterial and fungal pathogens but are not thought to control viral infection. This study showed that enhanced resistance against cucumber mosaic virus is caused by a tobacco calmodulin-like protein, rgs-CaM, which detects and counteracts the major viral virulence factor (RNA silencing suppressor) after SAR induction. rgs-CaM-mediated SAR illustrates the growth vs. defense trade-off in plants, as it targets the major virulence factor only under specific biotic stress conditions, thus avoiding the cost of constitutive activation while reducing the damage from virus infection.
外文关键词：systemic acquired resistance; calmodulin-like protein; RNA silencing suppressor; cucumber mosaic virus; priming; RNA interference; innate immunity; plant viruses; salicylic acid signaling
作者：Jeon, Eun Jin; Tadamura, Kazuki; Murakami, Taiki; 等
作者单位：北海道大学
期刊名称：JOURNAL OF VIROLOGY
期刊影响因子：4.663
出版年份：2017
出版刊次：10
点击下载：利用rgs-CaM检测和抵抗植物免疫启动中的病毒RNA沉默抑制子研究