Streptophyte algae and the evolution of nuclear control over plastid function

陆地植物在陆地宏观生物群中占主导地位。在过去的几年里，研究人员已经开始意识到，曾经被认为是陆地植物特有的植物生物学的许多特征，实际上是在它们的藻类祖先链藻中进化出来的。在被认为在向陆地过渡期间支持链藻的一系列特征中，包括激素应激反应信号、与有益的土壤微生物的交流、防止暴露在紫外线辐射下以及特殊细胞壁的存在。后者对于重要的植物性状尤其重要，例如对陆地胁迫、强光和干旱的耐受性。然而，这些因素也直接影响到光合作用的细胞器，即叶绿体。尽管人们对链藻和促进向陆地过渡的排泄物的兴趣与日俱增，但在向陆地生物过渡的过程中，叶绿体的作用还没有被以实验的方式考虑过。较高分枝的链藻与陆地植物的质体比与较低分枝的或其他藻类的质体更相似。与此同时，较高分枝的链柄藻类通过基因丢失和转移到细胞核，显示出核对质体功能的控制增强的迹象。更重要的是，初步的基因组数据揭示了越来越多的核因子调控链藻体内的叶绿体转录和对叶绿体信号的反应。在这里，我建议研究胚生质体的链藻起源，最终形成维管植物的多功能细胞器，这些细胞器可以分化为淀粉体、有色体和许多其他细胞器。将通过来自每个主要链藻藻类群的一名代表的全球基因表达谱来分析叶绿体-核通讯的进化。藻类将在受控生长条件下培养，并将通过高光和低温处理对叶绿体功能的扰动来探索差异基因表达。我将重点介绍质膜蛋白(顺行)和叶绿体到细胞核(逆行)信号因子基因的差异表达。这项计划将首次对链藻中的叶绿体-核通讯进行系统的调查，目的是探索在链芽植物中植物叶绿体-核通讯的逐步进化。同时，还将产生有关链藻分子生理学的关键数据。这些数据将使我能够检验这样一种假设，即植物体内目前的核控制程度是在链柄植物进化过程中产生的，这种从细胞器到细胞核的转变在地球上植物生命的出现中发挥了关键作用。

Land plants dominate the terrestrial macroscopic biome. Over the last few years, researchers have begun to appreciate that many features of plant biology that were once deemed land-plant specific in fact evolved in their algal progenitors, the streptophyte algae. Among the list of features that are believed to have supported the streptophyte algae during the transition to land are hormonal stress response signalling, communication with beneficial soil microbionts, protection against exposure to UV radiation and the presence of specialised cell walls. The latter are especially crucial for important plant traits such as tolerance to the terrestrial stressors high light and drought. These factors, however, also have a direct impact on the photosynthetic organelles, the plastids (chloroplasts). Although interest in streptophyte algae and the exaptations that faciliated the transition to land is growing, the role of the plastid in the shift to terrestrial life has not been considered in an experimental fashion. The plastids of higher branching streptophyte algae are more similar to those of land plants than to those of lower branching ones or those of other algae. Concomitantly, higher branching streptophyte algae show signs of increased nuclear control over plastid function by virtue of gene loss and transfer to the nucleus. What is more, preliminary genomic data reveal a growing repertoire of nuclear factors regulating plastid transcription and response to plastid signals within streptophyte algae. Here I propose to investigate the streptophyte algal origin of embryophyte plastids, culminating in the versatile organelle of vascular plants that can differentiate into amyloplasts, chromoplasts and many others. The evolution of plastid-nucleus communication will be analysed through global gene expression profiling of one representative from each major streptophyte algal group. Algae will be cultivated under controlled growth regimes and differential gene expression will be explored through perturbation of plastid function with high light and cold treatments. I will focus on the differential expression of genes for plastidal proteins (anterograde) and plastid to nucleus (retrograde) signalling factors. This proposal will conduct the first systematic survey of plastid-nucleus communication in streptophyte algae, with the goal of exploring the stepwise evolution of plant plastid-nucleus communication in streptophytes. At the same time crucial data on the molecular physiology of streptophyte algae will be generated. These data will allow me to test the hypothesis that the present degree of nuclear control over plastid function in plants emerged during streptophyte evolution, a shift from organelle to nucleus that played a critical role in the emergence of plant life on Earth.