The role of plastid-encoded RNA polymerase-associated proteins (PAPs) in chloroplast biogenesis of plants

质体编码的RNA聚合酶相关蛋白（PAP）在植物叶绿体生物发生中的作用

• 批准号: 456013568
• 负责人: Professor Dr. Thomas Pfannschmidt
• 金额: --
• 依托单位: Institut für Botanik
• 依托单位国家: 德国
• 项目类别: Research Grants
• 资助国家: 德国
• 项目状态: 未结题
• 来源: https://gepris.dfg.de/gepris/projekt/456013568?language=en
• 关键词: role; plastid; encoded; RNA; polymerase

Chloroplasts are the specific cell organelles of plants which perform the process of photosynthesis. They represent the structural and functional base for the energetic and metabolic support of the terrestrial biosphere including mankind. Without chloroplasts life of higher order as we know it today would be impossible. Despite this eminent role of these organelles for life on Earth understanding of essential molecular regulatory steps of their biogenesis is still elusive. Chloroplasts typically emerge from undifferentiated precursors, the proplastids, or from arrested developmental stages, the etioplasts. These differentiation processes are strictly light-dependent as becoming evident from a dark-grown seedling exposed to light. Within a few hours the yellow, chlorophyll-free cotyledons become green and develop photosynthetically active chloroplasts. This requires active and rapid regulation of thousands of genes that encode structural and functional components of chloroplasts. Most of these genes are encoded in the cell nucleus and their gene products need to be imported into the plastids after cytosolic translation. However, a small set of genes is encoded in the plastid-own genome, the plastome, and need to be expressed by the organelles themselves. Therefore, for a successful biogenesis of chloroplasts a tight coordination of the nuclear and plastid genomes is mandatory. An important key role in this coordination plays the plastid encoded RNA polymerase (PEP). This enzyme transcribes the genes of the plastome together with another nuclear encoded RNA polymerase (NEP). The PEP is comprised of four core subunits that are highly similar to those of prokaryotic RNA polymerases representing a remnant of the endosymbiotic ancestry of plastids. All four subunits are encoded in the plastome and are expressed exclusively by the NEP enzyme. Biochemical and molecular-genetic experiments have subsequently shown, that the PEP core complex is further expanded by the physical addition of 12 nuclear-encoded subunits during the initial steps of chloroplast biogenesis. These additional subunits were named PEP-associated proteins (PAPs) and they are of eminent importance since lack of any of them blocks chloroplast development ending finally in an albino phenotype of the corresponding mutant. PAPs, thus, represent apparently key components of chloroplast biogenesis. In this project we aim to unravel their specific role during chloroplast biogenesis. We emphasize to study their involvement in the phytochrome-mediated light signalling network, their expression regulation as well a their time-dependent assembly into the PEP complex. Special focus will be given to their potential function as retrograde signals from plastids towards the cell nucleus, a fascinating new idea for this still not understood signalling route that potentially allows plastids to control their own biogenesis.

叶绿体是植物特有的细胞器，进行光合作用。它们是包括人类在内的陆地生物圈的能量和代谢支持的结构和功能基础。没有叶绿体，我们今天所知的高级生命就不可能存在。尽管这些细胞器对地球上的生命有着重要的作用，但对其生物发生的重要分子调控步骤的理解仍然是难以捉摸的。叶绿体通常是从未分化的前体（前质体）或发育停滞阶段（黄化体）中产生的。这些分化过程严格依赖于光，从暴露于光的黑暗生长的幼苗变得明显。在几个小时内，黄色的无叶绿素子叶变成绿色，并发育出具有光合作用活性的叶绿体。这需要对编码叶绿体结构和功能成分的数千个基因进行积极和快速的调节。这些基因中的大多数在细胞核中编码，并且它们的基因产物需要在胞质翻译后输入到质体中。然而，一小部分基因编码在质体自身的基因组（质体组）中，需要由细胞器本身表达。因此，对于叶绿体的成功生物发生，核和质体基因组的紧密协调是强制性的。质体编码的RNA聚合酶（PEP）在这种协调中起着重要的关键作用。这种酶与另一种核编码的RNA聚合酶（NEP）一起转录质体基因。PEP由四个核心亚基组成，这些亚基与原核RNA聚合酶的亚基高度相似，代表了质体内共生祖先的残余。所有四个亚基都在质体中编码，并且仅由NEP酶表达。随后的生物化学和分子遗传学实验表明，PEP核心复合物在叶绿体生物发生的初始步骤中通过物理添加12个核编码亚基而进一步扩展。这些额外的亚基被命名为PEP相关蛋白（PAP），它们具有显著的重要性，因为缺乏它们中的任何一个都会阻止叶绿体发育，最终导致相应突变体的白化病表型。因此，PAP显然代表叶绿体生物发生的关键组分。在这个项目中，我们的目标是解开他们在叶绿体生物发生的具体作用。我们着重研究它们参与光敏色素介导的光信号网络，它们的表达调控以及它们的时间依赖性组装成PEP复合物。将特别关注它们作为从质体到细胞核的逆行信号的潜在功能，这是一个迷人的新想法，这个仍然不理解的信号传导途径可能允许质体控制自己的生物发生。