烟草曲茎病毒(TbCSV)单独侵染可诱导寄主产生严重症状，但伴随β卫星(TbCSB)时症状加重，是不完全依赖β卫星的双生病毒致病类型的典型代表；除明确RNA沉默抑制子是症状决定因子外，其余蛋白是否参与症状形成及其作用机理仍不清楚。我们在前期研究中发现利用PVX载体表达TbCSV AC3蛋白可在本氏烟上加重PVX的症状，本项目拟在此基础上通过构建TbCSV AC3突变体侵染性克隆并借助PVX载体介导基因表达技术明确AC3蛋白对病毒致病性的影响及其功能域；利用转基因、蛋白互作、高通量测序和生物信息学软件并结合TRV介导基因沉默技术明确AC3蛋白增强病毒致病性途径中的关键寄主因子，进而揭示AC3蛋白与寄主互作的途径和方式，最终解析AC3蛋白增强TbCSV/TbCSB致病性的作用机制。项目的实施可望为进一步阐明双生病毒/β卫星病害复合体致病机理提供更详尽的科学依据，也可为植物抗病毒育种提供新思路。

Tobacco curly shoot virus (TbCSV) is a typical begomovirus that not stringent in requirement for a betasatellite. TbCSV can infect host plants and induce disease symptoms in the presence or absence of its betasatellite (TbCSB), and TbCSB is not necessary for infection but intensifies symptoms in a host-dependent manner. Although previous studies have revealed suppressors of RNA silencing encoded by TbCSV and TbCSB are symptom determinants, whether and how the othor proteins encoded by TbCSV involved in symptom induction is still unknown. In our previous studies, PVX-based overexpression of TbCSV AC3 intensified disease symptoms on Nicotiana tabacum. Based on these results, we are going to construct the infectious clone of TbCSV AC3 mutant and use PVX mediated gene expression so as to elucidate the effect of AC3 protein on the pathogenicity of virus and its functional domain. By using transgenic technology, protein interaction and high-throughput sequencing and bioinformatics software combined with the TRV-mediated gene silencing, we are going to investigate the key pathways / factors that AC3 protein involved in and reveal the roles of AC3 protein acting in the host, and finally illustrate the mechanism how AC3 protein intensifies TbCSV/TbCSB pathogenicity. The implementation of the project is expected to provide a more scientific basis for further elucidating the pathogenic mechanism of the begomovirus/betasatellite disease complex, as well as providing new ideas for plant antiviral breeding.