Chloroplasts play a crucial role in essential processes such as photosynthesis and the synthesis of primary and diverse secondary metabolites. Recent studies have also highlighted their significance linked to phytohormone production in plant immunity, especially SA and JA. Ubiquitination, a key post-translational modification, usually leads to target protein degradation, which acts as a signal for remodeling the proteome via the induction of protein endocytosis or targeting to other membrane associated systems. Previously, the potato E3 ligase StRFP1 was shown to enhance resistance against Phytophthora infestans, but its mechanism remained unclear. Here, we demonstrate that StRFP1 interacted with the dually localized plastid glucose 6-phosphate transporter StGPT1 on the endoplasmic reticulum (ER). Transient expressed StGPT1-GFP located on the chloroplast and ER in plant cells. Overexpression of StGPT1 enhances late blight resistance in potato and Nicotiana benthamiana, activates immune responses including ROS bursts and up-regulation of PTI marker genes. The resistance function of StGPT1 seems to be related to its dual localization. Remarkably, StRFP1 ubiquitinates StGPT1 at the ER, possibly due to its merely transient function in peroxisomes, leading to apparent accumulation in chloroplasts. Our findings point to a novel mechanism by which a plant E3 ligase contributes to immunity via interacting with dually-targeted GPT1 at the ER of plant cells.

中文翻译：

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由 E3 泛素连接酶 StRFP1 介导的双靶向 StGPT1 在叶绿体中的积累可增强植物免疫力


叶绿体在光合作用以及初级和多种次生代谢物的合成等基本过程中发挥着至关重要的作用。最近的研究还强调了它们与植物免疫中植物激素产生的重要性，特别是 SA 和 JA。泛素化是一种关键的翻译后修饰，通常会导致靶蛋白降解，从而作为通过诱导蛋白质内吞作用或靶向其他膜相关系统来重塑蛋白质组的信号。此前，马铃薯E3连接酶StRFP1被证明可以增强对致病疫霉的抗性，但其机制仍不清楚。在这里，我们证明 StRFP1 与内质网 (ER) 上双重定位的质体葡萄糖 6-磷酸转运蛋白 StGPT1 相互作用。瞬时表达的 StGPT1-GFP 位于植物细胞的叶绿体和 ER 上。 StGPT1 的过度表达可增强马铃薯和本塞姆氏烟草的晚疫病抗性，激活免疫反应，包括 ROS 爆发和 PTI 标记基因的上调。 StGPT1的抵抗功能似乎与其双重定位有关。值得注意的是，StRFP1 在内质网泛素化 StGPT1，这可能是由于其在过氧化物酶体中的短暂功能，导致叶绿体中明显的积累。我们的研究结果指出了一种新机制，植物 E3 连接酶通过与植物细胞内质网的双重靶向 GPT1 相互作用来促进免疫。