Crosstalk between the chloroplast protein import and SUMO systems revealed through genetic and molecular investigation in Arabidopsis.
Crosstalk between the chloroplast protein import and SUMO systems revealed through genetic and molecular investigation in Arabidopsis.
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DOI：
10.7554/elife.60960
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发表时间：
2021-09-02
期刊：
影响因子：
7.7
通讯作者：
Jarvis RP
中科院分区：
文献类型：
--
作者：
Watson SJ;Li N;Ye Y;Wu F;Ling Q;Jarvis RP
叶绿体蛋白质组包含由核基因组编码的数千种不同的蛋白质。这些蛋白质通过TOC易位酶和相关下游系统的作用输入叶绿体。我们最近的工作表明，TOC复合物的稳定性是由泛素依赖的叶绿体相关蛋白降解途径动态调节的。在这里，我们证明TOC复合物也受到小泛素样修饰剂（SUMO）系统的调控。拟南芥突变体代表几乎整个SUMO接合途径可以部分抑制ppi 1的表型，ppi 1是一种缺乏Toc 33蛋白的淡黄色突变体。这种抑制与TOC蛋白质丰度的增加和叶绿体发育的改善有关。此外，从分子和生物化学实验的数据支持的模型，其中SUMO系统直接调节TOC蛋白质的稳定性。因此，我们已经确定了SUMO系统和叶绿体蛋白质进口机械之间的监管联系。所有的绿色植物都是通过将光能转化为化学能而生长的。它们利用一种叫做光合作用的过程来做到这一点，这种过程发生在植物细胞中称为叶绿体的隔间内。叶绿体使用成千上万种不同的蛋白质来制造化学能。其中一些蛋白质允许叶绿体利用叶绿素吸收光能，叶绿素是使叶子变绿色的色素。这些蛋白质中的绝大多数通过一种称为TOC复合物的蛋白质机器转运到叶绿体中。当植物缺乏TOC复合物的部分时，它们的叶绿体发育异常，它们的叶子变黄。光合作用会产生有毒的副产品，因此细胞在压力下需要一种方法来关闭它;例如，通过减少叶绿体上TOC复合物的数量。这是通过用一种叫做泛素的分子标记TOC复合物来实现的，这将导致它们从叶绿体中去除，减缓光合作用。目前尚不清楚是否有另一种类似的分子标记SUMO有助于这种破坏过程。为了找到答案，沃森等人研究了拟南芥的一种突变体。这种突变体具有低水平的TOC复合物，使其叶片变成浅黄色。遗传、分子和生化实验的结合表明，SUMO分子标签控制叶绿体上TOC复合物的水平。增加突变植物中SUMO的数量使它们的叶子变黄，而干扰负责沉积SUMO标签的基因则使叶子变绿色。这意味着在SUMO标签较少的植物中，细胞停止破坏它们的TOC复合物，使叶绿体发育得更好，并改变叶子的颜色。TOC复合物的SUMO标记与泛素标记系统有许多遗传相似性。SUMO标签可能有助于控制CHLORAD途径，该途径破坏标记有泛素的TOC复合物。了解这种关系，以及如何影响它，可以帮助提高作物的性能。下一步是确切地了解SUMO标签如何促进TOC复合体的破坏。
The chloroplast proteome contains thousands of different proteins that are encoded by the nuclear genome. These proteins are imported into the chloroplast via the action of the TOC translocase and associated downstream systems. Our recent work has revealed that the stability of the TOC complex is dynamically regulated by the ubiquitin-dependent chloroplast-associated protein degradation pathway. Here, we demonstrate that the TOC complex is also regulated by the small ubiquitin-like modifier (SUMO) system. Arabidopsis mutants representing almost the entire SUMO conjugation pathway can partially suppress the phenotype of ppi1, a pale-yellow mutant lacking the Toc33 protein. This suppression is linked to increased abundance of TOC proteins and improvements in chloroplast development. Moreover, data from molecular and biochemical experiments support a model in which the SUMO system directly regulates TOC protein stability. Thus, we have identified a regulatory link between the SUMO system and the chloroplast protein import machinery. All green plants grow by converting light energy into chemical energy. They do this using a process called photosynthesis, which happens inside compartments in plant cells called chloroplasts. Chloroplasts use thousands of different proteins to make chemical energy. Some of these proteins allow the chloroplasts to absorb light energy using chlorophyll, the pigment that makes leaves green. The vast majority of these proteins are transported into the chloroplasts through a protein machine called the TOC complex. When plants lack parts of the TOC complex, their chloroplasts develop abnormally, and their leaves turn yellow. Photosynthesis can make toxic by-products, so cells need a way to turn it off when they are under stress; for example, by lowering the number of TOC complexes on the chloroplasts. This is achieved by tagging TOC complexes with a molecule called ubiquitin, which will lead to their removal from chloroplasts, slowing photosynthesis down. It is unknown whether another, similar, molecular tag called SUMO aids in this destruction process. To find out, Watson et al. examined a mutant of the plant Arabidopsis thaliana. This mutant had low levels of the TOC complex, turning its leaves pale yellow. A combination of genetic, molecular, and biochemical experiments showed that SUMO molecular tags control the levels of TOC complex on chloroplasts. Increasing the amount of SUMO in the mutant plants made their leaves turn yellower, while interfering with the genes responsible for depositing SUMO tags turned the leaves green. This implies that in plants with less SUMO tags, cells stopped destroying their TOC complexes, allowing the chloroplasts to develop better, and changing the colour of the leaves. The SUMO tagging of TOC complexes shares a lot of genetic similarities with the ubiquitin tag system. It is possible that SUMO tags may help to control the CHLORAD pathway, which destroys TOC complexes marked with ubiquitin. Understanding this relationship, and how to influence it, could help to improve the performance of crops. The next step is to understand exactly how SUMO tags promote the destruction of the TOC complex.