Early Steps in Organelle Evolution – How Unicellular Hosts Tame their Bacterial Endosymbionts

细胞器进化的早期步骤——单细胞宿主如何驯服细菌内共生体

• 批准号: 242685455
• 负责人: Professorin Dr. Eva C.M. Nowack
• 金额: --
• 依托单位: Institut für Mikrobielle Zellbiologie
• 依托单位国家: 德国
• 项目类别: Independent Junior Research Groups
• 财政年份: 2014
• 资助国家: 德国
• 起止时间: 2013-12-31 至 2020-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/242685455?language=en
• 关键词: Early; Steps; Organelle; Evolution; How

The endosymbiotic acquisition of mitochondria and plastids more than a billion years ago profoundly impacted origin and diversification of eukaryotes. To decipher the molecular mechanisms that lead to the transformation of a bacterial endosymbiont into a genetically integrated cell organelle, this projects aims at studying early stages in organellogenesis: the photosynthetic cyanobacterial endosymbionts (chromatophores) in the cercozoan amoeba Paulinella chromatophora and the beta-proteobacterial endosymbionts in the trypanosomatid Angomonas deanei.The first five years of funding resulted in the following insights. (i) In P. chromatophora, nucleus and chromatophore-encoded proteins are highly complementary. (ii) Many nuclear genes that compensate for gene losses from the chromatophore were acquired through horizontal gene transfers from bacterial donors. (iii) Genetic control over the chromatophore shifted substantially to the nucleus with around one third of the chromatophore proteome being composed of nucleus-encoded, chromatophore-targeted proteins. (iv) A ~200 amino acid-long N-terminal pre-sequence seems to target proteins into the chromatophore, however the signal marking short imported proteins (<90 amino acids) for import into the chromatophore remains unknown. (v) In A. deanei, only 8 nucleus-encoded endosymbiont-targeted proteins (ETPs) were identified, suggesting that A. deanei represents an earlier state of endosymbiont integration compared to P. chromatophora. The identified ETPs likely represent key players in gaining host control over the intracellular bacterium. (vi) Through the development of genetic tools for A. deanei we established this organism as efficient, genetically tractable endosymbiosis model in which targeted gene knock-outs can be generated and transgenes expressed from the nuclear genome. These tools were instrumental for the identification of distinct subcellular localizations of the ETPs over the endosymbiont envelope, division site, or cytoplasm. The inability to obtain homozygous gene knock-outs for three ETPs analyzed so far, suggests an essential function for these proteins.In this proposal for a one-year extension of the Emmy Noether program, we focus on exploring evolution, targeting mechanisms, and functional characterization of the ETPs in A. deanei. For this purpose, we aim (i) to develop a conditional gene knock-out system for A. deanei; (ii) to apply this conditional system to investigate the cellular functions of the ETPs; and (iii) to explore the evolution of molecular mechanism underlying the targeting of host proteins to the endosymbiont in A. deanei.This work is critical to our understanding of the molecular mechanisms through which a eukaryotic cell can gain control over an endosymbiotic bacterium and which can lead over evolutionary time to the complete merger of the two symbiotic partners into a highly efficient single organism.

十多亿年前，线粒体和质体的内生共生获得对真核生物的起源和多样化产生了深远的影响。为了破译细菌内共生体转化为遗传整合细胞器的分子机制，本项目旨在研究器官发生的早期阶段：尾虫阿米巴中的光合性蓝藻内共生体(色素团)和锥虫中的β-蛋白细菌内共生体。第一个五年的资助产生了以下见解。(I)在变色拟青霉中，核和生色团编码的蛋白质具有很强的互补性。(2)许多弥补着色团基因损失的核基因是通过细菌供体的水平基因转移获得的。(3)对发色团的遗传控制基本上转移到了细胞核，大约三分之一的发色团蛋白质组由核编码的、以发色团为靶标的蛋白质组成。(4)一个长约200个氨基酸的N-末端预序列似乎以蛋白质为靶标进入发色团，但标记短的进口蛋白(&lt；90个氨基酸)以进入发色团的信号尚不清楚。(5)在底色假单胞菌中，只鉴定到8个核编码的内共生体靶向蛋白(ETP)，这表明与变色假单胞菌相比，底氏假单胞菌代表了内共生体整合的早期状态。已鉴定的ETP很可能代表了宿主对细胞内细菌的控制。(Vi)通过开发用于丁香菇的遗传工具，我们建立了高效的、遗传上易处理的内生共生模型，在该模型中可以产生有针对性的基因敲除并从核基因组中表达转基因。这些工具有助于确定ETP在内共生体被膜、分裂部位或细胞质上的不同亚细胞定位。到目前为止分析的三个ETP无法获得纯合的基因敲除，这表明这些蛋白质具有重要的功能。在这项将Emmy Noether计划延长一年的建议中，我们专注于探索A.deanei中ETP的进化、靶向机制和功能特征。为此，我们的目标是(I)建立一个针对丁香菇的条件基因敲除系统；(Ii)应用该系统来研究ETP的细胞功能；以及(Iii)探索宿主蛋白靶向丁香菇内共生体的分子机制的演变。这项工作对于我们理解真核细胞控制内共生细菌的分子机制是至关重要的，它可以随着进化时间的推移导致两个共生伙伴完全合并为一个高效的单一有机体。

项目成果

Putative sponge biomarkers in unicellular Rhizaria question an early rise of animals

• DOI: 10.1038/s41559-019-0806-5
• 发表时间: 2019-03
• 期刊: Nature Ecology & Evolution
• 影响因子: 16.8
• 作者: B. Nettersheim;J. Brocks;Arne Schwelm;J. Hope;F. Not;M. Lomas;C. Schmidt;R. Schiebel;E. Nowack;P. De Deckker;J. Pawłowski;S. Bowser;I. Bobrovskiy;K. Zonneveld;M. Kučera;M. Stuhr;C. Hallmann

Mikrobielle Symbiosen und die Evolution neuer Organellen

微生物共生和新细胞器的进化

• DOI: 10.1007/s12268-019-1043-9
• 发表时间: 2019
• 期刊: BIOspektrum
• 作者: Oberleitner;Nowack;E.C.M.
• 通讯作者: E.C.M.