Nuclear-cytoplasmic partitioning of cucumber mosaic virus protein 2b determines the balance between its roles as a virulence determinant and an RNA-silencing suppressor.
Nuclear-cytoplasmic partitioning of cucumber mosaic virus protein 2b determines the balance between its roles as a virulence determinant and an RNA-silencing suppressor.
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黄瓜花叶病毒蛋白 2b 的核质分配决定了其作为毒力决定因子和 RNA 沉默抑制因子的作用之间的平衡
DOI：
10.1128/jvi.00284-14
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发表时间：
2014-05
影响因子：
5.4
通讯作者：
Carr JP
中科院分区：
文献类型：
--
作者：
Du Z;Chen A;Chen W;Liao Q;Zhang H;Bao Y;Roossinck MJ;Carr JP
黄瓜花叶病毒（CMV）2b蛋白是一种RNA沉默抑制因子，在CMV积累和毒力中发挥作用。IA亚组CMV株系的2b蛋白分布于细胞核和细胞质之间，但其生物学意义尚不确定。我们融合了一个额外的核定位信号（NLS）的2b蛋白亚组IA株Fny-CMV创建2b-NLS，并测试其对亚细胞分布，沉默和毒力的影响。额外的NLS增强了2b蛋白的核和核仁积累，但核和核仁富集与斑块测定中显著降低的沉默抑制子活性相关，并废除了转基因拟南芥中2b蛋白介导的microRNA活性破坏。核/核仁定位的2b蛋白具有至少一些抑制抗病毒沉默的能力，但这不足以防止拟南芥中较年轻的发育叶片从疾病中恢复。然而，增强核和核仁积累的2b增加毒性和加速症状的出现在老叶。拟南芥系携带突变体Dicer样等位基因的实验表明，受损的抑制活性解释了2b-NLS增强病毒积累的能力减弱。值得注意的是，2b-NLS产生的毒力增加与对microRNA或短干扰RNA调节的宿主功能的影响无关。因此，尽管核和核仁定位的2b蛋白在沉默抑制方面不如胞质定位的2b有效，但它增强了CMV毒力。我们建议，2b蛋白质之间的细胞质和核/核仁区室的分区允许CMV调节病毒积累和对宿主的损害之间的平衡，大概是为了最大限度地提高病毒的利益。重要性在这项工作中，主要发现是核/核仁定位的2b蛋白与CMV毒力密切相关，这与其对小RNA途径的影响无关。此外，这项工作支持的论点，即沉默抑制活性的CMV 2b蛋白主要是由2b蛋白的部分驻留在细胞质中发挥。因此，我们建议，2b蛋白质之间的细胞质和核/核仁隔间的分区允许CMV调节病毒积累和损害宿主之间的平衡，大概是为了最大限度地提高病毒的利益。
The Cucumber Mosaic Virus (CMV) 2b protein is an RNA-silencing suppressor that plays roles in CMV accumulation and virulence. The 2b proteins of subgroup IA CMV strains partition between the nucleus and cytoplasm, but the biological significance of this is uncertain. We fused an additional nuclear localization signal (NLS) to the 2b protein of subgroup IA strain Fny-CMV to create 2b-NLS and tested its effects on subcellular distribution, silencing, and virulence. The additional NLS enhanced 2b protein nuclear and nucleolar accumulation, but nuclear and nucleolar enrichment correlated with markedly diminished silencing suppressor activity in patch assays and abolished 2b protein-mediated disruption of microRNA activity in transgenic Arabidopsis. Nucleus/nucleolus-localized 2b protein possesses at least some ability to inhibit antiviral silencing, but this was not sufficient to prevent recovery from disease in younger, developing leaves in Arabidopsis. However, enhanced nuclear and nucleolar accumulation of 2b increased virulence and accelerated symptom appearance in older leaves. Experiments with Arabidopsis lines carrying mutant Dicer-like alleles demonstrated that compromised suppressor activity explained the diminished ability of 2b-NLS to enhance virus accumulation. Remarkably, the increased virulence that 2b-NLS engendered was unrelated to effects on microRNA- or short interfering RNA-regulated host functions. Thus, although nucleus- and nucleolus-localized 2b protein is less efficient at silencing suppression than cytoplasm-localized 2b, it enhances CMV virulence. We propose that partitioning of the 2b protein between the cytoplasmic and nuclear/nucleolar compartments allows CMV to regulate the balance between virus accumulation and damage to the host, presumably to maximize the benefit for the virus. IMPORTANCE In this work, the main finding is that nucleus/nucleolus-localized 2b protein is strongly associated with CMV virulence, which is independent of its effect on small RNA pathways. Moreover, this work supports the contention that the silencing suppressor activity of CMV 2b protein is predominantly exerted by that portion of the 2b protein residing in the cytoplasm. Thus, we propose that partitioning of the 2b protein between the cytoplasmic and nuclear/nucleolar compartments allows CMV to regulate the balance between virus accumulation and damage to the host, presumably to maximize the benefit for the virus.