A biological rationale for NMD in plants

动物、真菌和植物很久以前就分裂了，进化出了截然不同的生存策略。然而，它们共同起源的线索可以在所有真核生物中使用许多相同成分进行的保守过程中找到。基因表达就是这样一个过程，基因的开启和关闭、上下调节是生命的基础。调控基因活动的方法有很多。其中研究最少的一个涉及调节被称为mRNA的分子的稳定性；信使信号从细胞核中的基因转移到细胞质中制造蛋白质的地方。最近，人们发现了一种被称为NMD的机制，它过去被认为是mRNA的一种质量控制筛选，在“坏”mRNA命令产生错误的蛋白质之前破坏它，实际上监督着许多不同的mRNA，包括许多看起来正常的mRNA。对NMD通常可以检查的基因总数的工作估计可能多达5% -也许是1500个基因。为什么一个细胞不惜代价将大量基因复制到mRNA中，只是为了在mRNA的指令被执行之前再次迅速破坏它呢？我们一直在研究NMD不能正常工作的突变植物，通过研究对整个植物的影响，以及对植物所有mRNA水平的影响。这些分析已经确定了这种看似能量浪费的安排的潜在生物学原理。我们的工作表明，植物使用NMD来抑制它们在发现自己暴露于环境挑战（例如病原体攻击的气候变化）时迅速需要的mrna水平。这是有道理的，因为通过阻止NMD破坏特定的mRNA，植物可以使这些mRNA稳定，这样它们就可以被多次翻译，产生必要的蛋白质来应对植物面临的挑战。目前，我们已经有了植物细胞中间接和直接NMD靶点的列表。为了剖析环境和通过mRNA稳定性协调的基因调控之间的相互作用，我们首先需要确定直接靶标和哪些保守成分是指定哪个靶标所必需的。在这一点上，我们可以制造人工目标，这样我们就可以研究环境是如何向NMD发出信号的，我们可以梳理出这个古老过程介导的全方位反应。这项研究可以在理解植物与病原体和环境的相互作用方面带来应用效益，也可以为人为地有条件地调节mRNA信息的稳定性和可翻译性提供工具。

Animals, fungi and plants split a long time ago and have evolved very different life strategies. Nevertheless, clues to their common origin can be found in the form of conserved processes carried out using many of the same components in all eukaryotes. Gene expression is one such process and the ability to turn genes on and off, up and down is fundamental to life. There are many ways to regulate gene activity. One of the least studied involves regulating the stability of molecules known as mRNA; the messenger signals that move from the genes in the nucleus to where the proteins are made in the cytoplasm. Recently, it has been discovered that a mechanism called NMD, that used to be considered as a sort of quality control sift for mRNA, destroying 'bad' mRNA before it ordered the production of the wrong proteins, actually oversees lots of different mRNAs, including many that appear to be normal. A working estimate of the total number of genes that could typically be inspected by NMD could be as many as 5% - perhaps 1500 genes. Why would a cell go to the expense of copying lots of genes into mRNA only to quickly destroy the mRNA again before its instructions could be acted upon? We have been looking at mutant plants where NMD is not working properly, both by studying the consequences for the plant as a whole and by looking at the effect on all of the plant's mRNA levels. These analyses have identified a potential biological rationale for what appears to be an energetically wasteful arrangement. Our work indicates that plants use NMD to suppress the levels of mRNAs that they will need quickly if they find themselves exposed to an environmental challenge, such as a change in the climate of a pathogen attack. This makes sense because by stopping NMD from destroying specific mRNA the plant can make those mRNAs stable, so that they can be translated many times over to make the necessary proteins to deal with the challenge the plant faces. Presently we have a list of both indirect and direct NMD targets in the plant cell. To dissect the interaction between the environment and co-ordinated gene regulation via mRNA stability we first need to identify both the direct targets and which of the conserved components are required to specify which target. At that point we can make artificial targets so that we can study how the environment signals to NMD and we can tease out the full range of responses mediated by this ancient process. This research could have applied benefits in terms of understanding plant interactions with pathogens and the environment and also by providing the tools to artificially conditionally regulate the stability and hence translatability of mRNA messages.