Du Zhi-You, Chen Fei-Fei, Liao Qian-Sheng, Zhang Hua-Rong, Chen Yan-Fei, Chen Ji-Shuang
Institute of Bioengineering, Zhejiang Sci-Tech University, Hangzhou 310018, PR China.
College of Life Sciences, Zhejiang University, Hangzhou 310029, PR China.
J Gen Virol. 2007 Sep;88(Pt 9):2596-2604. doi: 10.1099/vir.0.82927-0.
Cucumber mosaic virus (CMV)-encoded 2b protein from subgroup IA or subgroup II was shown to be a determinant of virulence in many solanaceous hosts. In this study, the virulence of 2b proteins from subgroup IB strains was analysed using four intraspecies hybrid viruses, which were generated by precise replacement of the 2b open reading frame (ORF) in subgroup IA strain Fny-CMV with the 2b ORFs of four subgroup IB strains, Cb7-CMV, PGs-CMV, Rad35-CMV and Na-CMV, generating FCb7(2b)-CMV, FPGs(2b)-CMV, FRad35(2b)-CMV and FNa(2b)-CMV, respectively. FCb7(2b)-CMV was more virulent than Fny-CMV, and was similar in phenotype to its parental virus Cb7-CMV on the three Nicotiana species tested. FNa(2b)-CMV also was virulent on these host species, equivalent to Fny-CMV or Na-CMV. However, FRad35(2b)-CMV only caused mild mosaic or undetectable symptoms on all the host species tested, and was less virulent than Fny-CMV or Rad35-CMV. FPGs(2b)-CMV infected all the host species systemically, and induced either mosaic or barely visible symptoms, demonstrating that the inability of PGs-CMV to infect these three Nicotiana species was not due to its 2b protein. The diverse virulence was shown to be mediated by the 2b proteins rather than the C-terminal overlapping parts of the 2a proteins, and was associated with the level of viral progeny RNA accumulation in systemically infected leaves, but not with the rate of long-distance viral movement in host plants. Through analysis of encapsidation of viral RNAs, there was an apparent correlation between the virulence and the high level of encapsidated RNA 2 in virions of Fny-CMV, FCb7(2b)-CMV and FNa(2b)-CMV.
黄瓜花叶病毒（CMV）IA亚组或II亚组编码的2b蛋白在许多茄科宿主中被证明是毒力的决定因素。在本研究中，使用四种种内杂交病毒分析了IB亚组毒株2b蛋白的毒力，这四种杂交病毒是通过用四种IB亚组毒株Cb7-CMV、PGs-CMV、Rad35-CMV和Na-CMV的2b开放阅读框（ORF）精确替换IA亚组毒株Fny-CMV中的2b ORF而产生的，分别产生了FCb7(2b)-CMV、FPGs(2b)-CMV、FRad35(2b)-CMV和FNa(2b)-CMV。FCb7(2b)-CMV比Fny-CMV更具毒力，在测试的三种烟草属植物上，其表型与其亲本病毒Cb7-CMV相似。FNa(2b)-CMV在这些宿主物种上也具有毒力，与Fny-CMV或Na-CMV相当。然而，FRad35(2b)-CMV在所有测试的宿主物种上仅引起轻微花叶或不可检测的症状，且毒力低于Fny-CMV或Rad35-CMV。FPGs(2b)-CMV能系统感染所有宿主物种，并诱导花叶或几乎不可见的症状，表明PGs-CMV无法感染这三种烟草属植物不是由于其2b蛋白。结果表明，不同的毒力是由2b蛋白介导的，而不是由2a蛋白的C末端重叠部分介导的，并且与系统感染叶片中病毒子代RNA的积累水平相关，但与宿主植物中病毒长距离移动的速率无关。通过分析病毒RNA的包装情况，发现Fny-CMV、FCb7(2b)-CMV和FNa(2b)-CMV病毒粒子中毒力与高水平的RNA 2包装之间存在明显的相关性。
