The accumulation of misfolded proteins in the endoplasmic reticulum (ER) defines a condition called ER stress that induces the unfolded protein response (UPR). The UPR in mammalian cells attenuates protein synthesis initiation, which prevents the piling up of misfolded proteins in the ER. Mammalian cells rely on Protein Kinase RNA‐Like Endoplasmic Reticulum Kinase (PERK) phosphorylation of eIF2α to arrest protein synthesis, however, plants do not have a PERK homolog, so the question is whether plants control translation in response to ER stress. We compared changes in RNA levels in the transcriptome to the RNA levels protected by ribosomes and found a decline in translation efficiency, including many UPR genes, in response to ER stress. The decline in translation efficiency is due to the fact that many mRNAs are not loaded onto polyribosomes (polysomes) in proportion to their increase in total RNA, instead some of the transcripts accumulate in stress granules (SGs). The RNAs that populate SGs are not derived from the disassembly of polysomes because protein synthesis remains steady during stress. Thus, the surge in transcription of UPR genes in response to ER stress is accompanied by the formation of SGs, and the sequestration of mRNAs in SGs may serve to temporarily relieve the translation load during ER stress.

中文翻译：

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在玉米幼苗中展开的蛋白质反应过程中的翻译控制：没有PERK的生活。

内质网（ER）中错误折叠的蛋白质的积累定义了一种称为ER应激的条件，该条件诱导了未折叠的蛋白质反应（UPR）。哺乳动物细胞中的UPR减弱了蛋白质合成的启动，从而防止了ER中错误折叠的蛋白质堆积。哺乳动物细胞依赖eIF2α的蛋白激酶RNA样内质网激酶（PERK）磷酸化来阻止蛋白合成，但是植物没有PERK同源物，因此问题是植物是否响应ER胁迫来控制翻译。我们将转录组中RNA水平的变化与核糖体保护的RNA水平进行了比较，发现响应ER胁迫，翻译效率（包括许多UPR基因）下降了。翻译效率的下降是由于许多mRNA未按其总RNA的增加比例加载到多核糖体（多核糖体）上，而是一些转录物积聚在应激颗粒（SGs​​）中。组成SG的RNA并非来自多核糖体的分解，因为蛋白质合成在压力下保持稳定。因此，响应ER应激，UPR基因转录的激增伴随着SGs的形成，而SGs中mRNA的螯合可能有助于暂时缓解ER应激期间的翻译负荷。