In Escherichia coli, transcription-translation coupling is mediated by NusG. Although chloroplasts are descendants of endosymbiotic prokaryotes, the mechanism underlying this coupling in chloroplasts remains unclear. Here, we report transcription-translation coupling through AtNusG in chloroplasts. AtNusG is localized in chloroplast nucleoids and is closely associated with the chloroplast PEP complex by interacting with its essential component PAP9. It also comigrates with chloroplast ribosomes and interacts with their two components PRPS5 (uS5c) and PRPS10 (uS10c). These data suggest that the transcription and translation machineries are coupled in chloroplasts. In the atnusg mutant, the accumulation of chloroplast-encoded photosynthetic gene transcripts, such as psbA, psbB, psbC and psbD, was not obviously changed, but that of their proteins was clearly decreased. Chloroplast polysomic analysis indicated that the decrease in these proteins was due to the reduced efficiency of their translation in this mutant, leading to reduced photosynthetic efficiency and enhanced sensitivity to cold stress. These data indicate that AtNusG-mediated coupling between transcription and translation in chloroplasts ensures the rapid establishment of photosynthetic capacity for plant growth and the response to environmental changes. Therefore, our study reveals a conserved mechanism of transcription-translation coupling between chloroplasts and E. coli, which perhaps represents a regulatory mechanism of chloroplast gene expression. This study provides insights into the underlying mechanisms of chloroplast gene expression in higher plants.

中文翻译：

---

AtNusG，一种细菌来源的叶绿体类核蛋白，连接叶绿体转录和翻译机制，是拟南芥叶绿体基因正确表达所必需的

在大肠杆菌中，转录-翻译偶联由 NusG 介导。尽管叶绿体是内共生原核生物的后代，但叶绿体中这种偶联的潜在机制仍不清楚。在这里，我们报告了叶绿体中通过 AtNusG 进行的转录-翻译偶联。AtNusG 位于叶绿体类核中，并通过与其基本成分 PAP9 相互作用而与叶绿体 PEP 复合物密切相关。它还与叶绿体核糖体共迁移并与其两个组分 PRPS5 (uS5c) 和 PRPS10 (uS10c) 相互作用。这些数据表明转录和翻译机制在叶绿体中耦合。在atnusg突变体中，叶绿体编码的光合基因转录本的积累，如psbA、psbB、psbC和psbD，没有发生明显变化，但是他们的蛋白质明显减少了。叶绿体多体分析表明，这些蛋白质的减少是由于它们在该突变体中的翻译效率降低，导致光合效率降低和对冷胁迫的敏感性增强。这些数据表明，AtNusG 介导的叶绿体转录和翻译之间的耦合确保了植物生长的光合能力的快速建立和对环境变化的响应。因此，我们的研究揭示了叶绿体和大肠杆菌之间转录-翻译耦合的保守机制，这可能代表了叶绿体基因表达的调控机制。本研究提供了对高等植物叶绿体基因表达的潜在机制的见解。叶绿体多体分析表明，这些蛋白质的减少是由于它们在该突变体中的翻译效率降低，导致光合效率降低和对冷胁迫的敏感性增强。这些数据表明，AtNusG 介导的叶绿体转录和翻译之间的耦合确保了植物生长的光合能力的快速建立和对环境变化的响应。因此，我们的研究揭示了叶绿体和大肠杆菌之间转录-翻译耦合的保守机制，这可能代表了叶绿体基因表达的调控机制。本研究提供了对高等植物叶绿体基因表达的潜在机制的见解。叶绿体多体分析表明，这些蛋白质的减少是由于它们在该突变体中的翻译效率降低，导致光合效率降低和对冷胁迫的敏感性增强。这些数据表明，AtNusG 介导的叶绿体转录和翻译之间的耦合确保了植物生长的光合能力的快速建立和对环境变化的响应。因此，我们的研究揭示了叶绿体和大肠杆菌之间转录-翻译耦合的保守机制，这可能代表了叶绿体基因表达的调控机制。本研究提供了对高等植物叶绿体基因表达的潜在机制的见解。