Karyopherins, the nucleocytoplasmic transporters, participate in multiple RNA silencing stages by transporting associated proteins into the nucleus. Importin α is a member of karyopherins and has been reported to facilitate virus infection via nuclear import of viral proteins. Unlike other RNA viruses, silencing of importin α2 (α2i) by virus-induced gene silencing (VIGS) boosted the titre of bamboo mosaic virus (BaMV) in protoplasts, and inoculated and systemic leaves of Nicotiana benthamiana. The enhanced BaMV accumulation in importin α2i plants was linked to reduced levels of RDR6-dependent secondary virus-derived small-interfering RNAs (vsiRNAs). Small RNA-seq revealed importin α2 silencing did not affect the abundance of siRNAs derived from host mRNAs but significantly reduced the 21 and 22 nucleotide vsiRNAs in BaMV-infected plants. Deletion of BaMV TGBp1, an RNA silencing suppressor, compromised importin α2i-mediated BaMV enhancement. Moreover, silencing of importin α2 upregulated NbAGO10a, a proviral protein recruited by TGBp1 for BaMV vsiRNAs clearance, but hindered the nuclear import of NbAGO10a. Taken together, these results indicate that importin α2 acts as a negative regulator of BaMV invasion by controlling the expression and nucleocytoplasmic shuttling of NbAGO10a, which removes vsiRNAs via the TGBp1-NbAGO10a-SDN1 pathway. Our findings reveal the hidden antiviral mechanism of importin α2 in countering BaMV infection in N. benthamiana.

中文翻译：

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Importin α2 通过 NbAGO10a 介导的小 RNA 清除参与 RNA 干扰，对抗本塞姆氏烟草中竹花叶病毒的积累

核转运蛋白（核细胞质转运蛋白）通过将相关蛋白转运到细胞核中来参与多个 RNA 沉默阶段。Importin α 是核转运蛋白的成员，据报道可通过病毒蛋白的核输入促进病毒感染。与其他 RNA 病毒不同，通过病毒诱导的基因沉默 (VIGS)沉默输入蛋白 α2 (α2 i ) 可提高本塞姆氏烟草原生质体以及接种和内吸叶子中竹花叶病毒 (BaMV) 的滴度。输入α2i植物中BaMV积累的增强与RDR6依赖性次级病毒衍生的小干扰RNA（vsiRNA）水平的降低有关。Small RNA-seq 显示，importin α2 沉默不会影响源自宿主 mRNA 的 siRNA 丰度，但会显着减少 BaMV 感染植物中的 21 和 22 核苷酸 vsiRNA。BaMV TGBp1（一种 RNA 沉默抑制子）的缺失会损害输入蛋白 α2i介导的 BaMV 增强。此外，沉默 importin α2 上调 NbAGO10a（一种由 TGBp1 招募用于 BaMV vsiRNA 清除的前病毒蛋白），但阻碍 NbAGO10a 的核输入。综上所述，这些结果表明，输入蛋白 α2 通过控制 NbAGO10a 的表达和核质穿梭，充当 BaMV 入侵的负调节因子，从而通过 TGBp1-NbAGO10a-SDN1 途径去除 vsiRNA。我们的研究结果揭示了输入蛋白 α2 在对抗N中 BaMV 感染中隐藏的抗病毒机制。本塞米阿纳。