Life and Environmental Sciences and Gene Research Centre, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8571, Japan.
Plant Cell Physiol. 2017 Aug 1;58(8):1302-1312. doi: 10.1093/pcp/pcx092.
Plants are eukaryotes living mostly immotile in harsh environments. On occasion, it is beneficial for their survival to maintain a transcriptional response to an environmental stress longer than the stress lasts (transcriptional memory) and even to reiterate such a response more quickly or more strongly when the same stress is re-encountered (priming memory). In eukaryotes, transcription takes place in the context of chromatin, the packaging material of DNA. Chromatin regulation is often invoked when it comes to environmental transcriptional and priming memory in plants, but rarely chromatin-based regulation can be accurately assigned to a given aspect of transcription in vivo. The conserved eukaryotic chromatin-modifying system Polycomb/Trithorax can support both long-term stability and flexibility of gene expression in Drosophila. The main principles of Polycomb/Trithorax regulation will be outlined and illustrated with the best-studied case of environmental memory from Arabidopsis. Despite being complex, the Polycomb/Trithorax system relies on experimentally tractable elements in the form of DNA, termed Polycomb/Trithorax Responsive Elements. PREs/TREs are essentially memory DNA elements. Here, relevant information to identify PRE/TRE-like elements in plants is highlighted. Examples of priming memory in plants are discussed in relation to the first two reported putative memory DNA elements. Arguably, similar cases from plants can be conducive in dissecting the contribution of DNA-based from chromatin-based regulation of transcription, when two types of DNA elements are defined: those representing binding sites for the transcription factors determining the environmental response and those controlling memory by regulating chromatin modification dynamics, ultimately maintaining the corresponding transcriptional state.
植物是真核生物，大多生活在恶劣的环境中，无法移动。有时，为了在环境压力持续时间内保持对环境压力的转录反应（转录记忆），甚至在再次遇到相同压力时更快或更强地重复这种反应（启动记忆），对它们的生存是有益的。在真核生物中，转录发生在染色质的背景下，染色质是 DNA 的包装材料。当涉及到植物的环境转录和启动记忆时，通常会调用染色质调控，但很少有基于染色质的调控可以准确地分配给体内给定的转录方面。保守的真核染色质修饰系统 Polycomb/Trithorax 可以支持果蝇中基因表达的长期稳定性和灵活性。将概述 Polycomb/Trithorax 调节的主要原则，并以拟南芥环境记忆的最佳研究案例进行说明。尽管复杂，但 Polycomb/Trithorax 系统依赖于以 DNA 形式表示的可实验操作的元素，称为 Polycomb/Trithorax 反应元件。PREs/TREs 本质上是记忆 DNA 元件。在这里，突出了在植物中识别 PRE/TRE 样元件的相关信息。还讨论了与前两个报道的假定记忆 DNA 元件相关的植物启动记忆的例子。可以说，当定义两种类型的 DNA 元素时，来自植物的类似情况有助于从染色质调控转录的角度来剖析 DNA 调控和染色质调控的贡献：那些代表决定环境反应的转录因子结合位点的元素和那些通过调节染色质修饰动力学来控制记忆的元素，最终维持相应的转录状态。
