高效靶向降解烟草花叶病毒核酸的dsRNA筛选与大量制备

Screening and Large-Scale Preparation of dsRNA for Highly Targeted Degradation of Tobacco Mosaic Virus(TMV) Nucleic Acids

【目的】筛选高效靶向降解烟草花叶病毒(tobacco mosaic virus,TMV)的dsRNA,实现其大量制备,并探究其作用机制。【方法】以TMV编码的CP、MP、RdRP功能基因为靶序列,体外转录合成相应的dsRNA,浸润本氏烟(Nicotiana benthamiana),24 h后接种TMV,于接毒后2、3 d取样提取总RNA和蛋白质,以CP基因mRNA水平和蛋白水平为指标,结合TMV病毒生物学症状,综合评价各dsRNA对TMV的抑制效果。同时结合侵染性克隆TMV-30B在本氏烟烟株上的荧光表达现象和TMV在三生烟(Nicotiana tabacum var. Samsun NN)上的过敏性坏死反应(hypersensitive necrosis reaction),通过比较TMV基因组上6个靶序列相对应的dsRNA,筛选出高效抑制TMV的dsRNA片段。为了获取大量的dsRNA,将dsRNA对应的基因片段插入到原核表达载体L4440的双T7启动子之间,转化至RNase III缺陷型大肠杆菌(Escherichia coli)HT115(DE3)中,并对原核表达制备的dsRNA喷施烟草后生成的siRNA进行深度测序,比较外源施用dsRNA后,对TMV侵染的small RNA表达特征和富集带的影响。【结果】筛选出高效影响TMV CP基因表达的dsRNA RdRP1461-1774,并构建了可诱导形成目的 dsRNA的原核表达载体L4440-dsRdRP1461-1774,可在DE3中大量制备RdRP1461-1774的dsRNA,菌液中提取的dsRNA喷施于烟草上对TMV的防治效果显著。TMV-30B侵染本氏烟时荧光数量减少,并能够延长叶片萎蔫时间,在三生烟上施用时叶片枯斑数量明显减少。小RNA测序结果显示TMV侵染引起的RNAi过程中正义链和反义链以大致相等的频率产生siRNA,而外源性dsRNA的浸润会引起靶向区域siRNA的富集,siRNA反义链累积量骤增,对应的正义链累积量骤减,外源dsRNA的施用能够引起siRNA表达丰度的变化。【结论】通过比较dsRNA介导植物靶向抗TMV侵染的效果来筛选抗烟草花叶病毒的dsRNA序列,最终选定TMV RdRP基因上一段长313 bp的高效作用片段,该片段dsRNA能够高效与靶基因结合,降低染病植株烟草花叶病毒的表达量。同时构建了RdRP1461-1774基因的dsRNA原核表达系统,实现其低成本的高效量产,为后续dsRNA在植物病毒方面的防治应用打下了基础。

【Objective】The objective of this study is to screen the dsRNAs with high efficiency and targeting degradation of tobacco mosaic virus(TMV), achieve its mass preparation, and to explore the mechanism.【Method】Using CP, MP and RdRP genes encoded by TMV as target sequences, dsRNAs were synthesized in vitro and infiltrated into Nicotiana benthamiana. After 24 h, TMV was inoculated, total RNA and protein were extracted from samples 2 and 3 d after TMV inoculation, and the mRNA level and protein level of CP gene were used as indicators, combined with the biological symptoms of TMV, to comprehensively evaluate the inhibitory effect of each dsRNA on TMV. The fluorescence expression of TMV-30 B on N. benthamianas and the hypersensitive necrosis reaction of TMV on Nicotiana tabacum var. Samsun NN were also combined. The dsRNA fragments that efficiently inhibit TMV were screened by comparing the dsRNAs corresponding to the six target sequences on the TMV genome. In order to obtain a large number of dsRNAs, the corresponding gene fragments of dsRNAs were inserted between the double T7 promoters of the prokaryotic expression vector L4440 and transformed into RNase III deficient Escherichia coli HT115(DE3). And the si RNA generated after the prepared dsRNA spraying on tobacco was deeply sequenced to compare the effect of exogenous application of dsRNA on the small RNA expression characteristics and enrichment bands of TMV infestation.【Result】Rd RP1461-1774 dsRNAs with high effect on TMV CP gene expression were screened, and L4440-dsRdRP1461-1774 prokaryotic expression vector was constructed, which could induce the formation of target dsRNAs. The dsRNA extracted from bacteria solution could significantly inhibit TMV, when TMV-30 B was applied to infect tobacco, the number of fluorescence decreased, the time of leaf wilting prolonged, and the number of necrosis spots decreased significantly. The results of small RNA sequencing showed that in the RNAi process induced by TMV infection, the sense and antisense chains produced siRNA with approximately equal frequency, while the infiltration of exogenous dsRNA resulted in the enrichment of siRNA in the target area, and the accumulation of antisense chain of siRNA increased sharply, the cumulative value of the corresponding sense chain decreased sharply. The application of exogenous dsRNA could change the abundance of siRNA expression.【Conclusion】The targeted anti-TMV dsRNA sequences were screened by comparing the effects of dsRNA on the targeted anti-TMV infection in plants. Finally, a 313 bp long effective segment of RdRP gene was selected. This fragment of dsRNA can efficiently bind to the target gene and reduce the expression of TMV in infected plants. At the same time, a dsRNA prokaryotic expression system of Rd RP1461-1774 gene was constructed to achieve low-cost and high-efficiency production, which provided the basis for the follow-up application of dsRNAs in the control of plant virus.