SCO (synthesis of cytochrome c oxidase) proteins are involved in the insertion of copper during the assembly of cytochrome c oxidase (COX), the final enzyme of the mitochondrial respiratory chain. Two SCO proteins, namely, homolog of copper chaperone 1 and 2 (HCC1 and HCC2) are present in seed plants, but HCC2 lacks the residues involved in copper binding, leading to uncertainties about its function. In this study, we performed a transcriptomic and phenotypic analysis of Arabidopsis thaliana plants with reduced expression of HCC1 or HCC2. We observed that a deficiency in HCC1 causes a decrease in the expression of several stress-responsive genes, both under basal growth conditions and after applying a short-term high salinity treatment. In addition, HCC1 deficient plants show a faster decrease in chlorophyll content, photosystem II quantum efficiency and COX levels after salinity stress, as well as a faster increase in alternative oxidase capacity. Notably, HCC2 deficiency causes opposite changes in most of these parameters. Bimolecular fluorescence complementation analysis indicated that both proteins are able to interact. We postulate that HCC1 is a limiting factor for COX assembly during high salinity conditions and that HCC2 probably acts as a negative modulator of HCC1 activity through protein-protein interactions. In addition, a direct or indirect role of HCC1 and HCC2 in the gene expression response to stress is proposed.

中文翻译：

---

拟南芥SCO蛋白相反地影响盐胁迫下细胞色素c氧化酶水平和基因表达。

SCO（细胞色素C氧化酶的合成）蛋白在细胞色素C氧化酶（COX）（线粒体呼吸链的最终酶）的组装过程中参与了铜的插入。种子植物中存在两种SCO蛋白，即铜伴侣1和2的同系物（HCC1和HCC2），但HCC2缺乏参与铜结合的残基，导致其功能不确定。在这项研究中，我们对HCC1或HCC2表达降低的拟南芥植物进行了转录组和表型分析。我们观察到，在基础生长条件下和短期应用高盐度处理后，HCC1的缺乏会导致几种应激反应基因的表达下降。此外，HCC1缺陷型植物的叶绿素含量下降更快，盐分胁迫后光系统II的量子效率和COX含量，以及其他氧化酶容量的快速增加。值得注意的是，HCC2缺乏会导致大多数这些参数发生相反的变化。双分子荧光互补分析表明这两种蛋白都能够相互作用。我们假设HCC1是高盐度条件下COX组装的限制因素，并且HCC2可能通过蛋白质相互作用来充当HCC1活性的负调节剂。另外，提出了HCC1和HCC2在基因表达对应激的响应中的直接或间接作用。双分子荧光互补分析表明这两种蛋白都能够相互作用。我们假设HCC1是高盐度条件下COX组装的限制因素，并且HCC2可能通过蛋白质相互作用来充当HCC1活性的负调节剂。另外，提出了HCC1和HCC2在基因表达对应激的响应中的直接或间接作用。双分子荧光互补分析表明这两种蛋白都能够相互作用。我们假设HCC1是高盐度条件下COX组装的限制因素，并且HCC2可能通过蛋白质相互作用来充当HCC1活性的负调节剂。另外，提出了HCC1和HCC2在基因表达对应激的响应中的直接或间接作用。