School of Applied Biosciences, Kyungpook National University, Daegu, 702-701, Korea.
Department of Molecular Biology, Max Planck Institute for Developmental Biology, D-72076, Tübingen, Germany.
Plant J. 2015 Jun;82(6):1018-1029. doi: 10.1111/tpj.12874.
The THO/TREX complex mediates transport of nascent mRNAs from the nucleus towards the cytoplasm in animals, and has a role in small interfering RNA-dependent processes in plants. Here we describe five mutant alleles of Arabidopsis thaliana THO2, which encodes a core subunit of the plant THO/TREX complex. tho2 mutants present strong developmental defects resembling those in plants compromised in microRNA (miRNA) activity. In agreement, not only were the levels of siRNAs reduced in tho2 mutants, but also those of mature miRNAs. As a consequence, a feedback mechanism is triggered, increasing the amount of miRNA precursors, and finally causing accumulation of miRNA-targeted mRNAs. Yeast two-hybrid experiments and confocal microscopy showed that THO2 does not appear to interact with any of the known miRNA biogenesis components, but rather with the splicing machinery, implying an indirect role of THO2 in small RNA biogenesis. Using an RNA immunoprecipitation approach, we found that THO2 interacts with miRNA precursors, and that tho2 mutants fail to recruit such precursors into the miRNA-processing complex, explaining the reduction in miRNA production in this mutant background. We also detected alterations in the splicing pattern of genes encoding serine/arginine-rich proteins in tho2 mutants, supporting a previously unappreciated role of the THO/TREX complex in alternative splicing.
THO/TREX 复合物介导动物新生 mRNA 从细胞核向细胞质的运输，并在植物中发挥小干扰 RNA 依赖性过程的作用。在这里，我们描述了拟南芥 THO2 的五个突变等位基因，THO2 编码植物 THO/TREX 复合物的核心亚基。tho2 突变体表现出强烈的发育缺陷，类似于 miRNA（miRNA）活性受损的植物。一致地，不仅 siRNA 的水平在 tho2 突变体中降低，而且成熟 miRNA 的水平也降低。因此，触发了反馈机制，增加了 miRNA 前体的数量，最终导致 miRNA 靶向 mRNAs 的积累。酵母双杂交实验和共聚焦显微镜观察表明，THO2 似乎不与任何已知的 miRNA 生物发生成分相互作用，而是与剪接机制相互作用，暗示 THO2 在小 RNA 生物发生中发挥间接作用。使用 RNA 免疫沉淀方法，我们发现 THO2 与 miRNA 前体相互作用，而 tho2 突变体不能将这些前体募集到 miRNA 加工复合物中，这解释了在该突变背景下 miRNA 产生减少的原因。我们还在 tho2 突变体中检测到编码丝氨酸/精氨酸丰富蛋白的基因的剪接模式发生改变，支持 THO/TREX 复合物在可变剪接中以前未被认识到的作用。
