Chloroplasts are plant organelles responsible for photosynthesis and environmental sensing. Most chloroplast proteins are imported from the cytosol through the translocon at the outer envelope membrane of chloroplasts (TOC). Previous work has shown that TOC components are regulated by the ubiquitin-proteasome system (UPS) to control the chloroplast proteome, which is crucial for the organelle's function and plant development. Here, we demonstrate that the TOC apparatus is also subject to K63-linked polyubiquitination and regulation by selective autophagy, potentially promoting plant stress tolerance. We identify NBR1 as a selective autophagy adaptor targeting TOC components, and mediating their relocation into vacuoles for autophagic degradation. Such selective autophagy is shown to control TOC protein levels and chloroplast protein import and to influence photosynthetic activity as well as tolerance to UV-B irradiation and heat stress in Arabidopsis plants. These findings uncover the vital role of selective autophagy in the proteolytic regulation of specific chloroplast proteins, and how dynamic control of chloroplast protein import is critically important for plants to cope with challenging environments.

中文翻译：

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选择性自噬调节叶绿体蛋白输入并促进植物抗逆性

叶绿体是负责光合作用和环境传感的植物细胞器。大多数叶绿体蛋白是通过叶绿体外膜 (TOC) 的易位子从细胞质中输入的。先前的工作表明，TOC成分受到泛素蛋白酶体系统（UPS）的调节来控制叶绿体蛋白质组，这对于细胞器的功能和植物发育至关重要。在这里，我们证明 TOC 装置也受到 K63 连接的多泛素化和选择性自噬的调节，可能促进植物的胁迫耐受性。我们将 NBR1 确定为针对 TOC 成分的选择性自噬接头，并介导它们重新定位到液泡中以进行自噬降解。这种选择性自噬可以控制 TOC 蛋白水平和叶绿体蛋白输入，并影响拟南芥植物的光合作用以及对 UV-B 照射和热应激的耐受性。这些发现揭示了选择性自噬在特定叶绿体蛋白的蛋白水解调节中的重要作用，以及叶绿体蛋白输入的动态控制对于植物应对挑战性环境至关重要。