The uptake and conversion of a free‐living cyanobacterium into a photosynthetic organelle by the single‐celled Archaeplastida ancestor helped transform the biosphere from low to high oxygen. There are two documented, independent cases of plastid primary endosymbiosis. The first is the well‐studied instance in Archaeplastida that occurred ca. 1.6 billion years ago, whereas the second occurred 90–140 million years ago, establishing a permanent photosynthetic compartment (the chromatophore) in amoebae in the genus Paulinella. Here, we briefly summarize knowledge about plastid origin in the Archaeplastida and then focus on Paulinella. In particular, we describe features of the Paulinella chromatophore that make it a model for examining earlier events in the evolution of photosynthetic organelles. Our review stresses recently gained insights into the evolution of chromatophore and nuclear encoded DNA sequences in Paulinella, metabolic connectivity between the endosymbiont and cytoplasm, and systems that target proteins into the chromatophore. We also describe future work with Paulinella, and the potential rewards and challenges associated with developing further this model system.

中文翻译：

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Paulinella，一种了解质体原发性内共生的模型。

单细胞原生体祖先吸收自由生活的蓝藻并将其转化为光合细胞器，有助于将生物圈从低氧转变为高氧。有两个记录在案的、独立的质体原发性内共生病例。第一个是在 Archaeplastida 中得到充分研究的实例，发生在 ca。16 亿年前，而第二次发生在 90-1.4 亿年前，在Paulinella属的变形虫中建立了一个永久的光合室（色素细胞） 。在这里，我们简要总结一下Archaeplastida中质体起源的知识，然后重点关注Paulinella。特别是，我们描述了Paulinella的特征色素细胞，使其成为研究光合细胞器进化早期事件的模型。我们的综述强调最近获得了对Paulinella中色素细胞和核编码 DNA 序列的进化、内共生体和细胞质之间的代谢连通性以及将蛋白质靶向色素细胞的系统的见解。我们还描述了与Paulinella的未来工作，以及与进一步开发该模型系统相关的潜在回报和挑战。