植物RNA病毒是影响作物产量的重要病原物。病毒编码蛋白及非翻译区（UTR）在病毒侵染过程中发挥至关重要的作用。然而，对于马铃薯Y病毒属病毒，衣壳蛋白（CP）和UTR对病毒致病力的了解却非常有限。西瓜花叶病毒（WMV）是我国瓜类作物上的重要病毒。交叉保护是防治病毒病的有效手段，其中获得弱毒突变体并了解其作用机制是非常必要的。我们已获得弱毒株系WMV-13全序列及强毒株系WMV-9侵染性克隆，并证明CP是影响WMV致病力的决定因素。同时，二级结构预测发现WMV 3′-UTR的5′-端具有一个茎环结构，它在部分马铃薯Y病毒属中是保守的。本研究拟首先明确影响WMV致病力的CP氨基酸位点及3′-UTR二级结构，了解其分子机制，获得相应的弱毒突变体，分析其对野生型WMV的交叉保护作用及后代群体发生回复突变的频率。本研究可帮助我们了解病毒的侵染机制，可为利用交叉保护防治WMV提供指导。

Plant RNA viruses were most important pathogen affecting crop yield. Roles of virus endocing proteins including untranslated regions (UTR) play essential roles during virus infection. However, little is known how coat protein (CP) or UTR affecting virus pathogenesis in potyvirus. Watermelon mosaic virus (WMV) is one of most important virus disease in Cucurbitaceaecrops. Cross protection has shown as an important way to control virus disease. Obtaining attenuated mutants and understanding their mechanisms is very necessary. We have obtained the complete genome sequence of mild stain of WMV-13 and the infectious cDNA clone of high virulence strain of WMV-9. Results showed that CP was a determinant affecting viral pathogenicity. Meanwhile, a stem-loop structure was found at 5′-terminus of WMV 3′-UTR, which conserved in part of potyvirus. The project will try to reveal the amino acids within CP and the role of secondary structure in 3′-UTR determining WMV pathogenicity , and understand the mechanisms regulating their functions. The attenuated strains will be obtained, and cross protection on wild strain of WMV and reverse mutation frequency in progenies will be analyzed. The outcome will help us understanding the mechanism of virus infection and find potential way to control WMV through cross protection.