Department of Plant Pathology and Microbiology and Center for Plant Cell Biology, University of California, Riverside CA 92721.
Vector-borne Virus Research Center, Haixia Institute of Science and Technology, College of Plant Protection, Fujian Agriculture and Forestry University, Fuzhou, Fujian 350002, China.
Plant Physiol. 2018 Feb;176(2):1587-1597. doi: 10.1104/pp.17.01370. Epub 2017 Nov 28.
Small interfering RNAs (siRNAs) are processed from virus-specific dsRNA to direct antiviral RNA interference (RNAi) in diverse eukaryotic hosts. We have recently performed a sensitized genetic screen in Arabidopsis () and identified two related phospholipid flippases required for antiviral RNAi and the amplification of virus-derived siRNAs by plant RNA-dependent RNA polymerase1 (RDR1) and RDR6. Here we report the identification and cloning of - () from the same genetic screen. encodes a multispan transmembrane protein broadly conserved in plants and animals with two homologous human proteins known as magnesium transporters. We show that mutant plants display no developmental defects and develop severe disease symptoms after infection with a mutant (CMV) defective in RNAi suppression. is induced by CMV infection, particularly in veins, and is required for antiviral RNAi and RDR6-dependent biogenesis of viral siRNAs. AVI2 is also necessary for Dicer-like2-mediated amplification of 22-nucleotide viral siRNAs induced in mutant plants by infection, but dispensable for RDR6-dependent biogenesis of endogenous transacting siRNAs. Further genetic studies illustrate that AVI2 plays a partially redundant role with AVI2H, the most closely related member in the gene family, in RDR1-dependent biogenesis of viral siRNAs and the endogenous virus-activated siRNAs (vasi-RNAs). Interestingly, we discovered a specific genetic interaction of AVI2 with AVI1 flippase that is critical for plant development. We propose that AVI1 and AVI2 participate in the virus-induced formation of the RDR1/RDR6-specific, membrane-bound RNA synthesis compartment, essential for the biogenesis of highly abundant viral siRNAs and vasi-RNAs.
小干扰 RNA (siRNA) 由病毒特异性 dsRNA 加工而来，可在多种真核宿主中指导抗病毒 RNA 干扰 (RNAi)。我们最近在拟南芥中进行了一种敏化遗传筛选，鉴定出两种与磷脂翻转酶相关的基因，它们对于抗病毒 RNAi 以及由植物 RNA 依赖性 RNA 聚合酶 1 (RDR1) 和 RDR6 扩增病毒衍生的 siRNA 是必需的。在这里，我们报告了同一遗传筛选中 的鉴定和克隆。 编码一种多跨膜蛋白，在植物和动物中广泛保守，有两个同源的人类蛋白，称为镁转运蛋白。我们表明， 突变体植物在感染 RNAi 抑制缺陷的 (CMV) 突变体后，没有发育缺陷，但会出现严重的疾病症状。CMV 感染诱导 的表达，特别是在叶脉中，对于抗病毒 RNAi 和 RDR6 依赖性病毒 siRNA 的生物发生是必需的。AVI2 对于由感染诱导的 突变体植物中 Dicer-like2 介导的 22 核苷酸病毒 siRNA 的扩增也是必需的，但对于 RDR6 依赖性内源性反式作用 siRNA 的生物发生是可有可无的。进一步的遗传研究表明，AVI2 在 RDR1 依赖性病毒 siRNA 和内源性病毒激活的 siRNA (vasi-RNAs) 的生物发生中与最密切相关的 基因家族成员 AVI2H 发挥部分冗余作用。有趣的是，我们发现 AVI2 与 AVI1 翻转酶之间存在特定的遗传相互作用，这对于植物发育至关重要。我们提出 AVI1 和 AVI2 参与了病毒诱导的 RDR1/RDR6 特异性膜结合 RNA 合成区室的形成，这对于高度丰富的病毒 siRNA 和 vasi-RNAs 的生物发生是必需的。
