DNA甲基化是真核生物基因组中最常见的一种DNA共价修饰形式，siRNA （small interfering RNA）能够靶向同源DNA序列介导胞嘧啶胞嘧啶甲基化，这个过程被称为RNA介导的胞嘧啶甲基化（RdDM），其在调节基因表达、调控转座子的活动和防御病毒等方面发挥重要作用。水杨酸（Salicylic acid, SA）是植物抗病防御反应的一个关键信号分子，能够诱导防御相关的基因表达而获得系统抗性。研究表明SA途径能被RNA和DNA病毒激活,但其被病毒诱导的机制并不清楚。本项目通过亚硫酸盐测序技术检测由RNA病毒PVY编码的Hc-Pro蛋白是否在SA途径上游调控基因ACD6启动子的解甲基化过程中起作用，和研究Hc-Pro蛋白是否能够上调SA途径防御相关的基因(ACD6、NPR1、WAK1和PR1)的表达。为研究和探讨RNA病毒激活SA途径的可能原因提供理论依据。

Cytosine methylation is one of epigenetic information marked on the DNA sequence. In plants, small interfering RNAs (siRNAs) target homologous genomic DNA sequences for cytosine methylation. This process, known as RNA-directed DNA methylation (RdDM), plays an important role in transposon control, regulation of gene expression and virus resistance. Salicylic acid (SA), a key signaling molecule for plant disease resistance, is synthesized by plants to induce accumulation of pathogenesis-related (PR) proteins and establish both local and systemic acquired resistance (SAR) against a diverse range of pathogens.The SA pathway is typically activated by RNA viruses and DNA viruses, but the reason is not clear.In this study, we will focuse on that Hc-Pro protein encoded by PVY virus mediate a decrease in DNA methylation of repeat regions in the promoters of ACD6, an upstream regulator of the salicylic acid defense pathway, and if Hc-Pro protein activate expression of defense-related genes in the host plants.Thus, this study will indicate the reason that RNA virus activate the salicylic acid pathway.