Institute of Molecular Plant Biology, Swiss Federal Institute of Technology Zurich (ETH Zurich), Universitätstrasse 2, Zurich, 8092, Switzerland.
Institute of Plant Sciences, University of Bern, Altenbergrain 21, Bern, 3013, Switzerland.
Plant J. 2020 Aug;103(5):1796-1809. doi: 10.1111/tpj.14868. Epub 2020 Jun 28.
Arabidopsis encodes 10 ARGONAUTE (AGO) effectors of RNA silencing, canonically loaded with either 21-22 nucleotide (nt) long small RNAs (sRNAs) to mediate post-transcriptional gene silencing (PTGS) or 24 nt sRNAs to promote RNA-directed DNA methylation. Using full-locus constructs, we characterized the expression, biochemical properties and possible modes of action of AGO3. Although AGO3 arose from a recent duplication at the AGO2 locus, their expression patterns differ drastically, with AGO2 being expressed in both male and female gametes whereas AGO3 accumulates in aerial vascular terminations and specifically in chalazal seed integuments. Accordingly, AGO3 downregulation alters gene expression in siliques. Similar to AGO2, AGO3 binds sRNAs with a strong 5' adenosine bias, but unlike Arabidopsis AGO2, it binds 24 nt sRNAs most efficiently. AGO3 immunoprecipitation experiments in siliques revealed that these sRNAs mostly correspond to genes and intergenic regions in a manner reflecting their respective accumulation from their loci of origin. AGO3 localizes to the cytoplasm and co-fractionates with polysomes to possibly mediate PTGS via translation inhibition.
拟南芥编码了 10 种 ARGONAUTE（AGO）RNA 沉默效应因子，通常负载 21-22 个核苷酸（nt）长的小 RNA（sRNA），以介导转录后基因沉默（PTGS），或负载 24 nt 的 sRNA 以促进 RNA 指导的 DNA 甲基化。我们利用全基因座构建体，对 AGO3 的表达、生化特性和可能的作用模式进行了表征。尽管 AGO3 是 AGO2 基因座的近期重复产生的，但它们的表达模式截然不同，AGO2 在雄性和雌性配子中均有表达，而 AGO3 在气生维管束末端和特异地在合点种子内表皮中积累。因此，AGO3 的下调会改变种荚中的基因表达。与 AGO2 相似，AGO3 与 sRNA 结合具有强烈的 5' 腺苷偏好性，但与拟南芥 AGO2 不同的是，它最有效地结合 24 nt 的 sRNA。在种荚中进行的 AGO3 免疫沉淀实验表明，这些 sRNA 主要对应于基因和基因间区域，其积累方式反映了它们各自从起源部位的积累情况。AGO3 定位于细胞质中，并与多核糖体共分离，可能通过翻译抑制来介导 PTGS。
