Abstract：
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.
摘要：
环状RNA（CircRNAs）在不同的生物过程中发挥重要作用；然而，它们的起源和功能，尤其是在植物中，基本上还不清楚。这里,我们用了两个玉米自交系,以及14种具有不同干旱敏感性的衍生RIL，在水分充足（WW）和水分胁迫（WS）条件下系统地表征玉米根中的8,790个circRNAs。我们发现一组不同的circRNAs在WS下以显著更高的水平表达。circRNAs的表达增强与较长的侧翼内含子和长散布的核元素（LINE）逆转录转座因子的富集有关。在circRNA产生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，H3K36me3/H3K4me1水平升高，H3K9Ac/H3K27Ac水平降低。我们发现表达circRNAs的基因受到宽松的选择。性状相关位点沿其基因区域的显着富集表明，产生circRNAs的基因与干旱胁迫下的植物存活率有关，暗示circRNAs在植物干旱反应中发挥作用。此外，我们发现circMED16的过度表达是干旱响应的circRNAs之一，增强拟南芥（拟南芥）的耐旱性。我们的结果为理解表观遗传修饰的复杂相互作用以及它们如何在干旱胁迫下对circRNA表达的微调做出贡献提供了一个框架。
