How to build a chloroplast: Unravelling chloroplast communication with the nucleus.

叶绿体是植物光合作用的家园，因此在植物功能水平和全球环境方面都是一个至关重要的细胞器。这个内共生细胞器保留了自己的南海岸生物科学博士培训伙伴关系（SoCoBio DTP）电子邮件：socobio@soton.ac.uk网站：www.southcoastbiosciencesdtp潜在的影响，以及任何特别适合该项目的候选品质（最多300字）减少的基因组和合成蛋白质的能力，但其约3000个蛋白质的大部分在细胞核中编码并运输到发育中的叶绿体。因此，叶绿体的发育需要叶绿体和细胞核之间的通信，但叶绿体向细胞核发出信号的机制基本上是未知的。叶绿体到细胞核的通讯被称为逆行信号，我们知道，当突变或处理导致叶绿体受损，导致约1000个核编码基因下调时，就会发生逆行信号。对这种下调被取消的拟南芥突变体（称为基因组解偶联突变体或gun突变体）的分析，导致了目前的建议，即在叶绿体中合成的四吡罗，血红素，作为促进核基因表达的积极信号。对核基因表达影响最强的突变体是gun1。GUN1是一种功能未知的叶绿体定位蛋白，但我们最近发现它也与其他gun突变体一样调节四吡唑合成（Shimizu et al ., 2019， PNAS, 116, 24900）。该项目的目的是确定GUN1如何调节四吡咯途径，并验证GUN1作为逆行血红素信号受体的假设。在这样做时，该项目将处理下列问题：GUN1如何改变通过四吡咯途径的流动？2. 由于GUN1也参与叶绿体蛋白稳态的调控，那么叶绿体蛋白合成与四吡咯途径之间的关系是什么？3. GUN1与四吡咯生物合成相互作用的分子基础是什么？

The chloroplast is home to photosynthesis in plants and is therefore a critically important organelle, both at the level of plant function and in terms of the global environment. This endosymbiotic organelle retains its own South Coast Biosciences Doctoral Training Partnership (SoCoBio DTP) Email: socobio@soton.ac.uk Website: www.southcoastbiosciencesdtp potential impact, and any candidate qualities that would be particularly suitable for the project (300 words max.) reduced genome and capacity to synthesise proteins, but the majority of its ~3000 proteins are encoded in the nucleus and transported to the developing chloroplast. The development of the chloroplast therefore requires communication between the chloroplast and the nucleus, but the mechanism by which the chloroplast signals to the nucleus is essentially unknown. Chloroplast-to-nucleus communication is termed retrograde signalling and we do know that it happens as mutations or treatments leading to damaged chloroplasts results in the down-regulation of ~1000 nuclear-encoded genes. Analysis of Arabidopsis mutants in which this down regulation is abrogated, called genomes uncoupled or gun mutants, have led to the current proposal that the tetrapyrrole, heme, synthesised in the chloroplast, acts as a positive signal to promote nuclear gene expression. The strongest mutant in terms of its effect on nuclear gene expression is gun1. GUN1 is a chloroplast-localised protein of unknown function, but we have recently shown that it also regulates tetrapyrrole synthesis in keeping with the other gun mutants (Shimizu et al, 2019, PNAS, 116, 24900). The aim of this project will be to determine how GUN1 regulates the tetrapyrrole pathway and test the hypothesis that GUN1 functions as a receptor for the retrograde heme signal. In doing so the project will address the following questions: 1. How does GUN1 alter the flow through through the tetrapyrrole pathway? 2. As GUN1 is also implicated in the regulation of chloroplast protein homeostasis, what is the relationship between chloroplast protein synthesis and the tetrapyrrole pathway? 3. What is the molecular basis of GUN1 interaction with tetrapyrrole biosynthesis?