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) 具有许多在自然界中具有不同病理特性的毒株。在这项研究中，我们专注于两种 CMV 分离株在诱导番茄（Solanum lycopersicum简历。世界一）。在初始感染阶段，接种 CMV-D8 和 CMV-Y 的植物出现绿色/黄色全身花叶和发育迟缓。在感染后期，CMV-D8 引起严重的全身症状，新出现的叶子出现 SLB，而 CMY-Y 引起严重的黄色花叶和发育不良。初始感染期间 CMV-D8 病毒 RNA 的积累高于 CMV-Y，但它们的水平在接种后 5 周没有显着差异。CMV-D8 和 CMV-Y 基因组 RNA 之间的假重组和重组分析表明，含有 2a 的 C 端区域和 CMV-D8 的整个 2b 蛋白的重组体（D2a-C/D2b）诱导了 SLB。将 2a ORF 中第 830 位的异亮氨酸变为缬氨酸在慢性 SLB 的形成中起重要作用。AGO1参与 RNA 沉默，以及HD-ZIP、TCP4和PHAN，它们对叶片形态发生至关重要。目前的结果首先表明 D2a-C/D2b 的协同功能在 SLB 形成中不可或缺。此外，我们建议 D2a-C/D2b 区域干扰与 RNA 沉默和叶形态发生相关的 miRNA 途径，导致 CMV-D8 的毒力增强。