Streptophyte algae and the evolution of nuclear control over plastid function

陆地植物在陆地宏观生物群落中占主导地位。在过去的几年里，研究人员已经开始认识到，许多曾经被认为是陆地植物特有的植物生物学特征实际上是在它们的藻类祖先--链藻中进化而来的。据信，在向陆地过渡期间支持链霉菌藻类的特征包括激素应激反应信号，与有益的土壤微生物的交流，防止暴露于紫外线辐射和存在专门的细胞壁。后者对于重要的植物性状，如对陆地胁迫物、强光和干旱的耐受性尤其重要。然而，这些因素也直接影响光合作用的细胞器，质体（叶绿体）。虽然对链藻和促进向陆地过渡的适应作用的兴趣正在增长，但质体在向陆地生活转变中的作用尚未以实验的方式被考虑。高分枝链藻的质体与陆生植物的质体相似性大于低分枝链藻或其它藻类的质体。同时，较高分支的链藻显示出凭借基因丢失和转移到细胞核的核控制质体功能增加的迹象。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节质体转录和响应链藻内质体信号。在这里，我建议调查的Streptophyte藻类起源的胚质体，最终在多功能的细胞器的维管植物，可以分化成淀粉体，质体和许多其他。质核通讯的演变将通过全球基因表达谱的一个代表从每个主要的链藻藻类组进行分析。藻类将在受控的生长制度下培养，并将通过强光和冷处理扰动质体功能来探索差异基因表达。我将集中在差异表达基因的质体蛋白质（顺行）和质体细胞核（逆行）信号因子。该项目将首次对链藻中的质核通讯进行系统调查，目的是探索链藻中植物质核通讯的逐步进化。与此同时，将产生关于链藻藻类分子生理学的关键数据。这些数据将使我能够检验这样一个假设，即目前植物质体功能的核控制程度是在链霉菌进化过程中出现的，这是一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.