The RNA helicases AtMTR4 and HEN2 target specific subsets of nuclear transcripts for degradation by the nuclear exosome in Arabidopsis thaliana.
The RNA helicases AtMTR4 and HEN2 target specific subsets of nuclear transcripts for degradation by the nuclear exosome in Arabidopsis thaliana.
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RNA解旋酶ATMTR4和HEN2靶向核转录的特定特定子集，以通过拟南芥中的核外泌体降解。
DOI：
10.1371/journal.pgen.1004564
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发表时间：
2014-08
期刊：
影响因子：
4.5
通讯作者：
Gagliardi D
中科院分区：
文献类型：
--
作者：
Lange H;Zuber H;Sement FM;Chicher J;Kuhn L;Hammann P;Brunaud V;Bérard C;Bouteiller N;Balzergue S;Aubourg S;Martin-Magniette ML;Vaucheret H;Gagliardi D
RNA外泌体是真核细胞主要的3 ' -5 ' RNA降解机器，参与细胞核和细胞质RNA的加工、监视和周转。在酵母和人类中，外泌体的所有核功能都需要RNA解旋酶MTR4。我们发现拟南芥核心外泌体可以与两个相关的RNA解旋酶AtMTR4和HEN2结合。互反共免疫沉淀表明，每种RNA解旋酶与外泌体核心复合物和不同的特定蛋白质组共同纯化。虽然AtMTR4主要是核仁蛋白，但HEN2位于核质中，似乎被排除在核仁之外。我们之前已经证明，AtMTR4的主要作用是降解rRNA前体和rRNA成熟副产物。在这里，我们证明了HEN2参与了大量聚腺苷化核外泌体底物的降解，如snoRNA和miRNA前体，不完全剪接的mrna，以及由假基因和基因间区产生的假转录物。在mtr4突变体中只观察到这些外泌体底物靶点的微弱积累，这表明mtr4对拟南芥中非核糖体rna和隐转录物的降解有贡献，但作用较小。一致地，转基因转录后基因沉默（PTGS）在mtr4突变体中受到轻微影响，但在hen2突变体中增加，这表明主要是核质外泌体降解异常转基因rna以限制其进入PTGS途径。有趣的是，HEN2在绿藻、苔藓和陆地植物中都是保守的，但在后生动物和其他真核生物谱系中却没有。我们的数据表明，与人类和酵母相比，植物具有两种功能特异性的RNA解旋酶，分别帮助外泌体降解特定的核仁和核质RNA群体。细胞依靠许多RNA降解途径来确保编码和非编码RNA的正确和及时的加工和周转。RNA降解的另一个重要功能是快速消除错误加工的RNA物种、成熟副产物和经常由普遍转录产生的无功能RNA。真核细胞中主要的3 ' -5 ' RNA降解机器是外泌体，它由RNA解旋酶等辅助因子激活。在酵母和人类中，所有核外泌体靶点的加工、周转和监视都依赖于一种RNA解旋酶MTR4。我们在这里表明，拟南芥外泌体复合体可以与两个相关的RNA解旋酶MTR4和HEN2结合。MTR4和HEN2分别存在于核仁和核质室中，并针对不同的核RNA底物亚群被外泌体降解。绿藻、苔藓和陆生植物中均存在MTR4和HEN2同源物，这表明在整个绿色谱系中，外显体相关RNA解旋酶的功能双性是进化上保守的。新出现的图像是，尽管高度的序列保守，胞内分布，外泌体辅助因子的活性和功能在不同的真核生物中差异很大。
The RNA exosome is the major 3′-5′ RNA degradation machine of eukaryotic cells and participates in processing, surveillance and turnover of both nuclear and cytoplasmic RNA. In both yeast and human, all nuclear functions of the exosome require the RNA helicase MTR4. We show that the Arabidopsis core exosome can associate with two related RNA helicases, AtMTR4 and HEN2. Reciprocal co-immunoprecipitation shows that each of the RNA helicases co-purifies with the exosome core complex and with distinct sets of specific proteins. While AtMTR4 is a predominantly nucleolar protein, HEN2 is located in the nucleoplasm and appears to be excluded from nucleoli. We have previously shown that the major role of AtMTR4 is the degradation of rRNA precursors and rRNA maturation by-products. Here, we demonstrate that HEN2 is involved in the degradation of a large number of polyadenylated nuclear exosome substrates such as snoRNA and miRNA precursors, incompletely spliced mRNAs, and spurious transcripts produced from pseudogenes and intergenic regions. Only a weak accumulation of these exosome substrate targets is observed in mtr4 mutants, suggesting that MTR4 can contribute, but plays rather a minor role for the degradation of non-ribosomal RNAs and cryptic transcripts in Arabidopsis. Consistently, transgene post-transcriptional gene silencing (PTGS) is marginally affected in mtr4 mutants, but increased in hen2 mutants, suggesting that it is mostly the nucleoplasmic exosome that degrades aberrant transgene RNAs to limit their entry in the PTGS pathway. Interestingly, HEN2 is conserved throughout green algae, mosses and land plants but absent from metazoans and other eukaryotic lineages. Our data indicate that, in contrast to human and yeast, plants have two functionally specialized RNA helicases that assist the exosome in the degradation of specific nucleolar and nucleoplasmic RNA populations, respectively. Cells rely on a number of RNA degradation pathways to ensure correct and timely processing and turnover of both coding and non-coding RNAs. Another important function of RNA degradation is the rapid elimination of misprocessed RNA species, maturation by-products, and nonfunctional RNAs that are frequently produced by pervasive transcription. The main 3′-5′ RNA degradation machine in eukaryotic cells is the exosome, which is activated by cofactors such as RNA helicases. In yeast and human, processing, turnover and surveillance of all nuclear exosome targets depend on a single RNA helicase, MTR4. We show here that the Arabidopsis exosome complex can associate with two related RNA helicases, MTR4 and HEN2. MTR4 and HEN2 reside in nucleolar and nucleoplasmic compartments, respectively, and target different subsets of nuclear RNA substrates for degradation by the exosome. The presence of both MTR4 and HEN2 homologues in green algae, mosses and land plants suggest that the functional duality of exosome-associated RNA helicases is evolutionarily conserved in the entire green lineage. The emerging picture is that, despite a high degree of sequence conservation, intracellular distribution, activities and functions of exosome cofactors vary considerably among different eukaryotes.
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