Laboratory of Plant Pathology, Faculty of Agriculture, Department of Agricultural and Environmental Sciences, University of Miyazaki, Gakuenkibanadainishi 1-1, Miyazaki 889-2192, Japan.
Laboratory of Plant Pathology, Faculty of Agriculture, Department of Agricultural and Environmental Sciences, University of Miyazaki, Gakuenkibanadainishi 1-1, Miyazaki 889-2192, Japan.
Virus Res. 2020 Nov;289:198172. doi: 10.1016/j.virusres.2020.198172. Epub 2020 Sep 24.
Cucumber mosaic virus (CMV) has numerous strains with distinct pathological properties in nature. In this study, we focused on the distinct host-specificity of two isolates of CMV regarding induction of the shoestring-like leaf blade (SLB) in tomato (Solanum lycopersicum cv. Sekaiichi). During the initial infection stage, plants inoculated with CMV-D8 and CMV-Y developed green/yellow systemic mosaic and stunting. Late in infection, CMV-D8 caused severe systemic symptoms with SLB on the newly emerged leaves, whereas CMY-Y caused severe yellow mosaic with stunting. Accumulation of viral RNA of CMV-D8 during initial infection was higher than for CMV-Y, but their levels did not differ significantly at 5 weeks post inoculation. Pseudorecombination and recombination analyses between CMV-D8 and CMV-Y genomic RNAs showed that recombinant that contained the C-terminal region of 2a and the entire 2b protein of CMV-D8 (D2a-C/D2b) induced SLB. Changing isoleucine to valine at position 830 in the 2a ORF played an important role in formation of chronic SLB. We further elucidated that infection with CMV-D8 or the recombinant Y1Y2(D2a-C/D2b)D3, but not with CMV-Y, upregulated miRNAs and transcript levels of AGO1, which is involved in RNA silencing, and of HD-ZIP, TCP4, and PHAN, which are essential for leaf morphogenesis. The present results first demonstrated that the cooperative function of D2a-C/D2b is involved indispensably in SLB formation. In addition, we suggest that D2a-C/D2b region interferes with the miRNA pathway that is associated with RNA silencing and leaf morphogenesis, leading to the enhanced virulence of CMV-D8.
黄瓜花叶病毒（CMV）在自然界中有许多具有不同病理特性的株系。在本研究中，我们专注于两种 CMV 分离株在诱导番茄（Solanum lycopersicum cv. Sekaiichi）叶片呈线状（SLB）方面的明显宿主特异性。在初始感染阶段，接种 CMV-D8 和 CMV-Y 的植物表现出绿色/黄色系统花叶和矮化。在感染后期，CMV-D8 引起严重的系统性症状，并在新出现的叶片上出现 SLB，而 CMY-Y 引起严重的黄色花叶和矮化。在初始感染期间，CMV-D8 的病毒 RNA 积累量高于 CMV-Y，但在接种后 5 周时，它们的水平没有显著差异。CMV-D8 和 CMV-Y 基因组 RNA 之间的假重组和重组分析表明，含有 CMV-D8 的 C 末端 2a 和整个 2b 蛋白的重组（D2a-C/D2b）诱导 SLB。在 2a ORF 中第 830 位的异亮氨酸突变为缬氨酸在慢性 SLB 的形成中起着重要作用。我们进一步阐明，感染 CMV-D8 或重组 Y1Y2(D2a-C/D2b)D3，但不是感染 CMV-Y，会上调 miRNA 和 AGO1 的转录水平，AGO1 参与 RNA 沉默，HD-ZIP、TCP4 和 PHAN 是叶片形态发生所必需的。本研究结果首次表明，D2a-C/D2b 的协同功能在 SLB 形成中是必不可少的。此外，我们认为 D2a-C/D2b 区域干扰与 RNA 沉默和叶片形态发生相关的 miRNA 途径，导致 CMV-D8 的毒力增强。
