高温激活RNA沉默介导的心叶烟抗病毒防御反应

High temperature activate RNA silencing-mediated antiviral defense in tobacco plants

在真核细胞内,RNA沉默是一种保守的抵抗病毒及外源基因等寄生分子的防御机制。温度可以明显地影响植物体与病毒之间的相互作用。在常温状态下,常常会伴随病毒病的爆发,但在较高温度下,症状则会减轻,甚至有些感病植株新生叶片可以较快地恢复健康。目前这类现象的内在机制还不完全清楚。本文通过定量分析不同温度下马铃薯X病毒(Po-tatovirus X,PVX)和马铃薯Y病毒(Potato virus Y,PVY)侵染的心叶烟(Nicotiana glutinosa)植株体内病毒蛋白含量,结合症状观察,确定30℃左右是PVX和PVY在心叶烟上引起症状消失即发生系统性RNA沉默的临界温度,此时的感病植株上部新生展开叶片呈现无症状态,下部已发病叶片症状不变。在常温时,由病毒激发的RNA沉默会受到抑制,病毒来源的小分子干涉RNA(small interfering RNAs,siRNAs)含量极少或根本检测不到,植株对于病毒的敏感性较强。当温度达到30或32℃时,感病植株下部症状保持叶片中,病毒起源的siRNAs含量明显增加,而上部新生健康叶片中却检测不到siRNAs的存在。这说明高温激活了RNA沉默介导的植物抗病毒防御反应,导致病毒症状减轻甚至消失。

RNA silencing is a conserved defense system of eukaryotic cells, which operates against molecular parasites including viruses and transgenes. Temperature dramatically affects plant-virus interactions. Outbreaks of virus diseases are frequently associated with normal temperature, while viral symptoms are often attenuated and plants recover rapidly from virus diseases at high temperature. However, the underlying mechanisms of these well-known observations are not yet understood. Here, we report that 30℃ is the turning point at which Nicotiana glutinosa can recover from virus disease such as Potato virus X（PVX） and Potato virus Y（PVY） by activating system RNA silencing. The result was obtained by observing symptom development and quantifying viral protein and virus-derived small interfering RNAs （siRNAs） in N. glutinosa at different temperature. In room temperature, plants became more susceptible to viruses and virus-mediated RNA silencing was inhibited. Consistently, the levels of virus-derived siRNAs were low or never existed. In contrast, RNA silencing was activated and the amount of virus-derived siRNAs dramatically increased in lower leaves which remained symptom with rising temperature up to 30℃ or even higher, while in upper leaves which were symptomless, no siRNAs existed. All these suggested that high temperature activated RNA silencing-mediated antiviral defense in tobacco plants which resulted in symptom ease or even disappear.