Laboratory of Plant Pathology, Faculty of Agriculture, Department of Agricultural and Environmental Sciences, University of Miyazaki, Gakuenkibanadainishi 1-1, Miyazaki, 889-2192, Japan.
Virol J. 2020 Apr 7;17(1):49. doi: 10.1186/s12985-020-01303-3.
In Raphanus sativus (Japanese radish), strain D8 of cucumber mosaic virus (CMV-D8) establishes a systemic infection and induces mild mosaic on upper, non-inoculated leaves, whereas strain Y of CMV (CMV-Y) causes only a local infection in the inoculated leaves. Here, we further analyzed the specific viral factor(s) of CMV-D8 that is (are) indispensable for systemic infection in Japanese radish.
To identify which genomic RNA(s) is (are) involved in systemic infection in radish, we carried out a pseudorecombination analysis between CMV-D8 and CMV-Y. With recombination analyses between CMV-D8 and CMV-Y using mutant/recombinant RNA2s, chimeric and point-mutated RNA3s, we identified viral factors that are indispensable for systemic infection.
Viral RNA2 and RNA3 of CMV-D8 facilitated efficient virus spread into the upper, non-inoculated plant tissues of radish (cv. Tokinashi), but not those of CMV-Y. Recombinant RNA2s demonstrated that the 2b protein (2b) and the C-terminus of the 2a protein (2a) of CMV-D8 have a crucial role in systemic infection. In addition, we used chimeric and point-mutated RNA3s to that Pro and Pro in the coat protein (CP) of CMV-D8 are involved in efficient systemic infection and that Ser in the 3a protein (3a) of CMV-D8 has positive effects on systemic spread. The results suggested that these viral factors facilitate systemic infection of CMV-D8 in Japanese radish.
The C-terminal region of 2a, the entire region of 2b, and supplementary function of either Ser in 3a or Pro/Pro in CP confer systemic infectivity on CMV-D8 in radish. These results further elucidate the complex interaction of viral proteins of CMV to complete systemic infection as a host-specific manner.
在萝卜中，黄瓜花叶病毒（CMV）的 D8 株系建立全身性感染，并在上部非接种叶片上引起轻微花叶，而 CMV 的 Y 株系仅在接种叶片上引起局部感染。在这里，我们进一步分析了 CMV-D8 株系中建立系统性感染所必需的特定病毒因子。
为了确定与萝卜系统感染相关的基因组 RNA，我们进行了 CMV-D8 和 CMV-Y 之间的假重组分析。利用 CMV-D8 和 CMV-Y 之间的重组分析，对 RNA2 和 RNA3 进行突变/重组，鉴定出对系统性感染必不可少的病毒因子。
CMV-D8 的 RNA2 和 RNA3 促进了病毒在萝卜（Tokinashi 品系）上部非接种植物组织中的有效传播，但 CMV-Y 的 RNA2 和 RNA3 则不能。重组 RNA2 表明，CMV-D8 的 2b 蛋白和 2a 蛋白的 C 末端在系统感染中起关键作用。此外，我们还利用嵌合和点突变的 RNA3，表明 CMV-D8 的 CP 中的 Pro 和 Pro 参与了有效的系统感染，而 CMV-D8 的 3a 蛋白中的 Ser 对系统传播有积极影响。结果表明，这些病毒因子促进了 CMV-D8 在萝卜中的系统感染。
2a 蛋白的 C 末端、2b 蛋白的全长以及 3a 蛋白中的 Ser 或 CP 中的 Pro/Pro 的补充功能赋予了 CMV-D8 在萝卜中系统性感染的能力。这些结果进一步阐明了 CMV 病毒蛋白之间的复杂相互作用，以特定宿主的方式完成系统性感染。
