Circular RNAs (CircRNAs) play an important role in diverse biological processes; however, their origin and functions, especially in plants, remain largely unclear. Here, we used two maize (Zea mays) inbred lines, as well as 14 of their derivative RILs with different drought sensitivity, to systematically characterize 8,790 circRNAs in maize roots under well-watered (WW) and water-stress (WS) conditions. We found that a diverse set of circRNAs expressed at significantly higher levels under WS. Enhanced expression of circRNAs was associated with longer flanking introns and an enrichment of long interspersed nuclear element (LINE) retrotransposable elements. The epigenetic marks found at the back-splicing junctions of circRNA-producing genes were markedly different from canonical splicing, characterized by increased levels of H3K36me3/H3K4me1, as well as decreased levels of H3K9Ac/H3K27Ac. We found that genes expressing circRNAs are subject to relaxed selection. The significant enrichment of trait-associated sites along their genic regions suggested that genes giving rise to circRNAs were associated with plant survival rate under drought stress, implying that circRNAs play roles in plant drought responses. Furthermore, we found that overexpression of circMED16, one of the drought-responsive circRNAs, enhances drought tolerance in Arabidopsis (Arabidopsis thaliana). Our results provide a framework for understanding the intricate interplay of epigenetic modifications and how they contribute to the fine-tuning of circRNA expression under drought stress.

中文翻译：

---

玉米根部干旱诱导的环状 RNA：从噪声中分离信号

环状RNA（CircRNA）在多种生物过程中发挥着重要作用；然而，它们的起源和功能，尤其是在植物中的起源和功能，在很大程度上仍不清楚。在这里，我们使用了两个玉米（Zea mays）自交系，以及它们的 14 个具有不同干旱敏感性的衍生 RIL，系统地表征了水分充足（WW）和水分胁迫（WS）条件下玉米根中的 8,790 个 circRNA。我们发现，在 WS 下，多种不同的 circRNA 的表达水平明显更高。 circRNA 表达的增强与较长的侧翼内含子和长散布核元件 (LINE) 逆转录转座元件的富集有关。在产生circRNA的基因的反向剪接连接处发现的表观遗传标记与典型剪接明显不同，其特征是H3K36me3/H3K4me1水平增加，以及H3K9Ac/H3K27Ac水平降低。我们发现表达 circRNA 的基因受到宽松的选择。基因区域性状相关位点的显着富集表明，产生 circRNA 的基因与干旱胁迫下植物的存活率相关，这意味着 circRNA 在植物干旱反应中发挥作用。此外，我们发现 circMED16（一种干旱响应性 circRNA）的过度表达可增强拟南芥（Arabidopsis thaliana）的耐旱性。我们的结果为理解表观遗传修饰复杂的相互作用以及它们如何在干旱胁迫下微调 circRNA 表达提供了一个框架。