Chloroplast-Associated Degradation (CHLORAD): Molecular definition of a ubiquitin-dependent system for plastid protein removal in plants

叶绿体相关降解 (CHLORAD)：植物中质体蛋白去除泛素依赖性系统的分子定义

• 批准号: BB/R009333/1
• 负责人: Paul Jarvis
• 金额: $ 68.44万
• 依托单位: University of Oxford
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2018
• 资助国家: 英国
• 起止时间: 2018 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=BB%2FR009333%2F1
• 关键词: Chloroplast; Associated; Degradation; CHLORAD; Molecular

The human population is growing rapidly and set to reach 9bn by 2050, and there is ever increasing pressure on natural resources. Thus, the drivers for increased crop yields and resilience to climate change and sub-optimal growing conditions are stronger than ever. To meet these demands it will be essential to develop improved crop varieties. Through research on the model plant thale cress, we recently made a significant breakthrough: We discovered a gene called SP1 that controls important aspects of plant growth, including plant responses to adverse environmental conditions such as water stress and high salinity (collectively, abiotic stresses). Thale cress plants can be made more tolerant of such stresses by modifying SP1 expression. Recently, we identified two new genes that function in the same regulatory pathway as SP1 - a pathway which we now term CHLORAD (for "Chloroplast-Associated Degradation"). In this project, we will study these new genes in detail, to elucidate their functions and understand how they work together with SP1, and in doing so we hope to identify new strategies for crop improvement.Like SP1, the two new CHLORAD genes regulate the development of structures inside plant cells called chloroplasts. Chloroplasts are normal cellular constituents (i.e., they are organelles), and in many ways they define plants. They contain the green pigment chlorophyll and are responsible for photosynthesis, capturing sunlight energy and using it to power the activities of the cell. As photosynthesis is the only significant mechanism of energy-input into the living world, chloroplasts are of huge importance, not just to plants but to all life on Earth. Chloroplasts also have critical roles in plant responses to abiotic stress, and so are ideal targets for engineering stress tolerance in crops.Chloroplasts are composed of thousands of different proteins, and most of these are encoded by genes in the cell nucleus and so are synthesized outside of the organelle in the cellular matrix known as the cytosol. As chloroplasts are each surrounded by a double-membrane envelope, sophisticated machinery is needed to bring about the import of these proteins into the organelle. This comprises two molecular machines, one in each membrane, called TOC (for "Translocon at the Outer membrane of Chloroplasts") and TIC. Each machine is composed of several different proteins that work cooperatively.The SP1 gene encodes a regulatory factor called a "ubiquitin E3 ligase". Such regulators work by labelling-up unwanted proteins to target them for removal. The SP1 E3 ligase mediates the removal of TOC components, and thereby controls TOC functions so that only the desired proteins are imported by chloroplasts. Such control enables major functional changes of chloroplasts during development and in adaptation to stress. But TOC proteins are deeply embedded in the chloroplast outer membrane, presenting a physical obstacle to their removal following labelling by SP1. Our discovery of the new CHLORAD genes provides a clue as to how this obstacle is overcome: our unpublished data strongly suggest these genes encode key components of a molecular motor that drives the extraction of unwanted TOC proteins. We will study this CHLORAD machinery to understand more clearly how unwanted chloroplast proteins are removed.Moreover, the role of CHLORAD in environmental stress tolerance will be studied. We will explore how manipulating the activity of the pathway may be used to improve stress tolerance in plants. The pathway appears to operate in many different plant species, including major crops, and so our results have the potential to see broad application. Drought and salinity are among the most significant factors affecting crop yields, with annual global losses due to drought alone estimated at $10bn. We believe that our work on CHLORAD may help to alleviate such losses.

人口正在快速增长，预计到 2050 年将达到 90 亿，自然资源面临的压力也越来越大。因此，提高作物产量以及抵御气候变化和次优生长条件的驱动力比以往任何时候都更加强大。为了满足这些需求，开发改良作物品种至关重要。通过对模型植物拟南芥的研究，我们最近取得了重大突破：我们发现了一种名为 SP1 的基因，它控制植物生长的重要方面，包括植物对水分胁迫和高盐度（统称为非生物胁迫）等不利环境条件的反应。通过修改 SP1 表达，可以使拟南芥植物对此类胁迫具有更强的耐受性。最近，我们发现了两个新基因，它们与 SP1 具有相同的调控途径，我们现在将这条途径称为 CHLORAD（“叶绿体相关降解”）。在这个项目中，我们将详细研究这些新基因，阐明它们的功能并了解它们如何与 SP1 协同工作，并在此过程中我们希望确定作物改良的新策略。与 SP1 一样，这两个新的 CHLORAD 基因调节植物细胞内称为叶绿体的结构的发育。叶绿体是正常的细胞成分（即它们是细胞器），并且在许多方面它们定义了植物。它们含有绿色色素叶绿素，负责光合作用、捕获阳光能量并用其为细胞的活动提供动力。由于光合作用是向生命世界输入能量的唯一重要机制，叶绿体不仅对植物而且对地球上的所有生命都非常重要。叶绿体在植物对非生物胁迫的反应中也发挥着关键作用，因此是作物抗逆性工程的理想靶标。叶绿体由数千种不同的蛋白质组成，其中大部分由细胞核中的基因编码，因此在细胞核外合成细胞基质中的细胞器称为胞质溶胶。由于每个叶绿体都被双膜包膜包围，因此需要复杂的机器将这些蛋白质导入细胞器。它由两个分子机器组成，每个膜各有一个，称为 TOC（“叶绿体外膜的转运蛋白”）和 TIC。每台机器都由几种协同工作的不同蛋白质组成。SP1基因编码一种称为“泛素E3连接酶”的调节因子。此类调节剂的工作原理是标记不需要的蛋白质，以将其去除。 SP1 E3 连接酶介导 TOC 成分的去除，从而控制 TOC 功能，以便叶绿体仅输入所需的蛋白质。这种控制使得叶绿体在发育和适应应激过程中发生重大功能变化。但 TOC 蛋白深深嵌入叶绿体外膜中，这给 SP1 标记后的去除带来了物理障碍。我们对新 CHLORAD 基因的发现为如何克服这一障碍提供了线索：我们未发表的数据强烈表明这些基因编码分子马达的关键组件，该分子马达驱动提取不需要的 TOC 蛋白。我们将研究这种 CHLORAD 机制，以更清楚地了解如何去除不需要的叶绿体蛋白质。此外，还将研究 CHLORAD 在环境胁迫耐受性中的作用。我们将探索如何操纵该途径的活性来提高植物的胁迫耐受性。该途径似乎在许多不同的植物物种中发挥作用，包括主要作物，因此我们的结果有可能得到广泛应用。干旱和盐度是影响农作物产量的最重要因素之一，仅干旱造成的全球每年损失估计就达 100 亿美元。我们相信，我们在 CHLORAD 上的工作可能有助于减轻此类损失。

项目成果

Mutations in TIC100 impair and repair chloroplast protein import and impact retrograde signalling

TIC100 突变损害和修复叶绿体蛋白输入并影响逆行信号传导

• DOI: 10.1101/2022.01.18.476798
• 发表时间: 2022
• 作者: Loudya N

The chloroplast-associated protein degradation pathway controls chromoplast development and fruit ripening in tomato

• DOI: 10.1038/s41477-021-00916-y
• 发表时间: 2021-05-01
• 期刊: NATURE PLANTS
• 影响因子: 18
• 作者: Ling, Qihua;Sadali, Najiah Mohd;Jarvis, R. Paul
• 通讯作者: Jarvis, R. Paul

Mutations in the chloroplast inner envelope protein TIC100 impair and repair chloroplast protein import and impact retrograde signaling.

• DOI: 10.1093/plcell/koac153
• 发表时间: 2022-07-30
• 期刊: The Plant cell

Publisher Correction: The chloroplast-associated protein degradation pathway controls chromoplast development and fruit ripening in tomato.

出版商更正：叶绿体相关蛋白降解途径控制番茄有色体发育和果实成熟。

• DOI: 10.1038/s41477-021-01018-5
• 发表时间: 2021
• 期刊: Nature plants
• 影响因子: 18
• 作者: Ling Q