Regulation of poly(A) RNA retention in the nucleus as a survival strategy of plants during hypoxia

Last finding indicates that post-transcriptional processes are significant in low-oxygen conditions, but their nature is poorly understood. Here, we localized poly(A) RNA and mRNA coding proteins involved and not involved with resistance to hypoxia in <i>Lupinus luteus</i> and <i>Arabidopsis thaliana</i> during submergence and after recovery of aerobic conditions. We showed a strong nuclear accumulation of poly(A) RNA and 6 of 7 studied mRNAs with a concurrent strong reduction in RNA polymerase II transcription during hypoxia. In this study, the nucleus did not accumulate mRNA of the <i>ADH1</i> (alcohol dehydrogenase 1) gene, which is a core hypoxia gene. The RNA accumulation in the nucleus is among the mechanisms of post-transcriptional gene regulation that prevents translation. However re-aeration was accompanied by a strong increase in the amount of the mRNAs in the cytoplasm and a simultaneous decrease in nuclear mRNAs. This finding indicates that the nucleus is a storage site for those of mRNAs which are not involved in the response to hypoxia for use by the plants after the hypoxic stress. In this study, the highest intensity of RNA accumulation occurred in Cajal bodies (CBs); the intensity of accumulation was inversely correlated with transcription. Under hypoxia, <i>ncb-1</i> mutants of <i>Arabidopsis thaliana</i> with a complete absence of CBs died sooner than wild type (WT), accompanied by a strong reduction in the level of poly(A) RNA in the nucleus. These results suggest that the CBs not only participate in the storage of the nuclear RNA, but they also could take part in its stabilization under low-oxygen conditions.

最新研究表明，转录后（post-transcriptional）过程在低氧环境中具有重要意义，但目前对其本质的理解仍十分有限。本研究针对淹水胁迫及恢复有氧条件过程中，黄羽扇豆（Lupinus luteus）与拟南芥（Arabidopsis thaliana）体内参与和不参与低氧耐受的编码蛋白mRNA以及聚腺苷酸RNA（poly(A) RNA）进行了原位定位分析。我们发现，低氧条件下，聚腺苷酸RNA以及7种研究mRNA中的6种会在细胞核中大量积累，同时RNA聚合酶II（RNA polymerase II）的转录活性显著降低。本研究中，作为核心低氧基因的<i>ADH1</i>（乙醇脱氢酶1，alcohol dehydrogenase 1）的mRNA并未在细胞核中积累。细胞核内的RNA积累属于抑制翻译的转录后基因调控机制之一。然而，复氧处理后，细胞质中的mRNA含量显著升高，而细胞核内的mRNA水平则同步下降。这一结果表明，细胞核可作为不参与低氧应答的mRNA的储存位点，供植物在低氧胁迫结束后使用。本研究中，RNA积累强度最高的区域为卡哈尔体（Cajal bodies，CBs），且其积累强度与转录活性呈负相关。低氧条件下，完全缺失卡哈尔体的拟南芥<i>ncb-1</i>突变体较野生型（wild type，WT）更早死亡，且其细胞核内聚腺苷酸RNA的水平显著降低。上述结果表明，卡哈尔体不仅参与细胞核RNA的储存，还可能在低氧条件下参与RNA的稳定维持。