Evolution of Photosynthetic Organelles Based on Studies of the Thecamoeba Paulinella chromatophora

泡囊变形虫Paulinella chromatophora（Rhizaria）窝藏两个明显的光合单位，称为色素细胞，这代表蓝藻内共生体可能是途中成为“典型的”光合细胞器。色素体独立于质体进化，可能代表了更近的内共生事件。色素细胞基因组的大小介于自由生活的蓝藻和质体之间，这表明内共生体和宿主功能的整合正在进行中。最近报道了从色素细胞基因组到宿主核基因组的基因转移的第一个证据。该项目旨在探索从色素细胞到宿主核基因组的进一步基因转移的发生和模式，澄清蛋白质导入色素细胞是否像典型细胞器那样发生的问题，使用异源蓝藻系统检查转移基因编码的蛋白质的功能，并探索建立控制色素细胞生长和分裂的机制。我的工作的另一个重要目标将是产生一个纯培养的P. chromatophora，确定其营养需求和提高其生长速度，更广泛的目标是使这种独特的生物体的模型，阐明过程的核心光合细胞器的进化。

The thecamoeba Paulinella chromatophora (Rhizaria) harbors two conspicuous photosynthetic units, termed chromatophores, which represent cyanobacterial endosymbionts likely to be en route to becoming ‘typical’ photosynthetic organelles. The chromatophores evolved independently from plastids and likely represent a much more recent endosymbiotic event. The size of the chromatophore genome is intermediate between that of a free-living cyanobacterium and a plastid, suggesting that integration of endosymbiont and host functionalities is ongoing. The first evidence for gene transfer from the chromatophore genome to the nuclear genome of the host was recently reported. This project aims at exploring the occurrence and mode of further gene transfer from the chromatophore to the host nuclear genome, clarifying the question of whether protein import into the chromatophore occurs as in canonical organelles, examining the functionality of the proteins encoded by the transferred genes using a heterologous cyanobacterial system, and exploring mechanisms by which control over chromatophore growth and division was established. Another important aim of my work will be to generate an axenic culture of P. chromatophora, determine its nutritional requirements and improve its growth rate with the broader goal of making this unique organism a model for elucidating processes central to the evolution of a photosynthetic organelle.