围绕Cajal body研究双生病毒编码的V2蛋白调控植物DNA甲基化的分子机制

在植物中，RNA 介导的DNA甲基化 (RdDM) 负责从头DNA甲基化的建立，并在植物防御病毒中起着重要作用。在全球造成作物大量减产的双生病毒，复制时产生双链DNA中间体，正好是RdDM的靶向物。作为反击策略，双生病毒蛋白进化出抑制基因沉默的功能。我们近期成果揭示了双生病毒V2蛋白与RdDM途径中关键组件AGO4蛋白在Cajal body（细胞核内核糖核蛋白复合物成熟的场所）内互作，抑制依赖于Cajal body的病毒DNA甲基化。然而，V2蛋白是否及如何干扰植物或者宿主的DNA甲基化仍不清楚。我们初步结果表明，V2蛋白能改变植物DNA甲基化组和转录组，且部分变化与ago4突变体相吻合。以Cajal body为切入点，这项研究通过评估V2与AGO4的互作、V2在Cajal body中的定位与其影响植物甲基化组和转录组的关联，解析相应分子机制，为开发抗病毒策略和培育抗病毒作物提供新的方向。

In plants, the RNA-directed DNA methylation (RdDM) pathway, which is responsible for the establishment of de novo DNA methylation, plays a remarkable role in plant defence against viruses. The RdDM machinery is known to concentrate in the Cajal body, a subnuclear compartment that is the site of maturation of ribonucleoprotein complexes, but the biological significance of this localization has remained elusive so far. Geminiviruses, causing dramatic yield losses worldwide, replicate in the nucleus of the infected cell through double-stranded (ds) DNA intermediates, which are targeted by RdDM. As a counter-attack strategy, geminiviruses have evolved viral suppressors to prevent the viral genome from being methylated, and some viral suppressors could also manipulate the DNA methylation of the plant genome. Our recent results have uncovered the V2 protein, encoded by the geminivirus Tomato yellow leaf curl virus (TYLCV), can efficiently counters DNA methylation of the viral genome through targeting the central RdDM component AGO4 in the Cajal body and interfering with the ability of AGO4 to bind viral DNA. Furthermore, methylation of the viral genome and its suppression by V2 occur in a Cajal body-dependent manner. These findings provide a valuable entry point to gain understanding of the antagonism between geminiviruses and plants through DNA methylation. However, whether V2 affects DNA methylation of the plant genome and, if so, the molecular mechanisms underlying how V2 causes these changes have remained largely elusive. Our preliminary results show that V2 alters genome-wide DNA methylation and transcriptome in the plant, in a partially similar pattern to that in ago4 mutant. Capitalizing on our previous work and on a large body of preliminary data, we expect that this study will provide unprecedented insight into how V2 affects the genome-wide DNA methylation and transcriptional landscape in the plant. On one hand, we will evaluate whether the interaction with AGO4 and localization in the Cajal body of V2 are required for its effect; on the other hand, if the V2-mediated changes are AGO4-dependent, we will attempt to unravel how V2 interferes with AGO4-dependent DNA methylation. Taken together, our results，from a new perspective, will help us to gain further understanding of the functional connection between the Cajal body, the regulation of DNA methylation, and anti-viral defence. This understanding is helpful for us to discover new target for generation of resistant plants in anti-viral defence.