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

泡状棘虫（根状棘虫）有两个明显的光合单位，称为色素团，它们代表蓝藻内共生体，可能正在成为“典型的”光合细胞器。色素体独立于质体进化而来，可能代表了一个更近期的内共生事件。染色质基因组的大小介于自由生活的蓝藻和质体之间，表明内共生体和宿主功能的整合正在进行中。最近报道了基因从染色质基因组转移到宿主核基因组的第一个证据。本项目旨在探索基因从染色质进一步转移到宿主核基因组的发生和模式，澄清蛋白质进入染色质是否像在典型细胞器中一样发生的问题，利用异源蓝藻系统检测转移基因编码的蛋白质的功能，并探索染色质生长和分裂的控制机制。我工作的另一个重要目标是产生一种无性培养的P. chroophora，确定其营养需求并提高其生长速度，更广泛的目标是使这种独特的生物成为阐明光合细胞器进化核心过程的模型。

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.