Mitochondria are key components of eukaryotic cells, so their proper functioning is monitored via different mitochondrial signalling responses. One of these mitochondria-to-nuclear 'retrograde' responses to maintain mitochondrial homeostasis is the mitochondrial unfolded protein response (UPRmt), which can be activated by a variety of defects including blocking mitochondrial translation, respiration, protein import or transmembrane potential. Although UPRmt was first reported in cultured mammalian cells, this signalling pathway has also been extensively studied in the nematode Caenorhabditis elegans. In yeast, there are no published studies focusing on UPRmt in a strict sense, but other unfolded protein responses (UPR) that appear related to UPRmt have been described, such as the UPR activated by protein mistargeting (UPRam) and mitochondrial compromised protein import response (mitoCPR). In plants, very little is known about UPRmt and only recently some of the regulators have been identified. In this paper, we summarise and compare the current knowledge of the UPRmt and related responses across eukaryotic kingdoms: animals, fungi and plants. Our comparison suggests that each kingdom has evolved its own specific set of regulators, however, the functional categories represented among UPRmt-related target genes appear to be largely overlapping. This indicates that the strategies for preserving proper mitochondrial functions are partially conserved, targeting mitochondrial chaperones, proteases, import components, dynamics and stress response, but likely also non-mitochondrial functions including growth regulators/hormone balance and amino acid metabolism. We also identify homologs of known UPRmt regulators and responsive genes across kingdoms, which may be interesting targets for future research.

中文翻译：

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跨界线粒体未折叠蛋白质相关反应：类似的问题，不同的调节器

线粒体是真核细胞的关键组成部分，因此通过不同的线粒体信号反应监测它们的正常功能。这些维持线粒体稳态的线粒体对核“逆行”反应之一是线粒体未折叠蛋白反应 (UPRmt)，它可以被多种缺陷激活，包括阻断线粒体翻译、呼吸、蛋白质输入或跨膜电位。尽管 UPRmt 最初是在培养的哺乳动物细胞中报道的，但这种信号通路也在线虫秀丽隐杆线虫中得到了广泛研究。在酵母中，没有严格意义上关注 UPRmt 的已发表研究，但已经描述了与 UPRmt 相关的其他未折叠蛋白反应 (UPR)，例如由蛋白质错误靶向激活的 UPR (UPRam) 和线粒体受损的蛋白质输入反应 (mitoCPR)。在植物中，对 UPRmt 知之甚少，直到最近才确定了一些调节剂。在本文中，我们总结并比较了真核生物界：动物、真菌和植物中 UPRmt 和相关反应的当前知识。我们的比较表明，每个王国都进化出了自己特定的一组调节因子，然而，UPRmt 相关靶基因中代表的功能类别似乎在很大程度上重叠。这表明保留适当线粒体功能的策略是部分保守的，针对线粒体伴侣蛋白、蛋白酶、导入成分、动力学和应激反应，但也可能是非线粒体功能，包括生长调节剂/激素平衡和氨基酸代谢。我们还确定了跨界已知 UPRmt 调节因子和响应基因的同源物，这可能是未来研究的有趣目标。