Molecular and developmental approach to understanding diversification in mediophyte diatoms

硅藻(微小的海洋植物)具有重要的生态和经济价值；的确，每五次吸入中的氧气来自硅藻，但其中一些会产生对人类有害的神经毒素。它们也是种类最丰富(约20万)的微藻，因此可以与陆地上开花植物的多样性相媲美。从进化的角度来看，硅藻和开花植物一样，是相对较新的物种，表明物种形成率非常高。我的长期研究目标是评估与硅藻繁殖相关的过程和结构的进化意义，以便了解自从硅藻首次出现在侏罗纪时期化石记录中以来，各种类型的性行为可能在硅藻的壮观多样性中发挥了什么作用。这项提议的直接目标是将生殖、发育和分子方法应用于硅藻进化史上两个主要转变的代表，以理清它们彼此之间及其与近亲的关系。我建议研究两个目的硅藻，它们目前似乎不太适合或不确定是否符合传统和分子系统学(“族谱”)。海藻类与它们的近亲有很大的不同，比都类很可能持有证据，表明最高级的硅藻--羽毛硅藻是现存的最接近的近亲。我们将寻找这些不适合或不确定的角色是如何形成的发育指标。我们将使用先进的显微技术(光学和荧光显微镜、扫描电子显微镜、X射线显微分析、二氧化硅特定染色)来检测和定位蛋白石二氧化硅(硅藻细胞壁的构建块)，并描述细胞壁组件在发育阶段的精细结构。在我们的系统发育推论中，我们还将使用迄今未得到充分利用的分子工具-ITS2共识二级结构模型。我们的调查工作表明，这些模型在解开硅藻系统发育关系方面的作用与它们在绿藻和其他植物中被证明的一样有用。在硅藻进化生物学中，对这些硅藻的系统发育分析与我们提出的个体发育方法相结合是一种新颖的方法。我们在大约十年前才开创了这种综合方法，是世界上唯一有系统地将繁殖数据添加到更广泛的硅藻进化生物学主体中的实验室。进一步发展的主要障碍是缺乏可重复的性诱导方案，我们现在已经为所涉及的硅藻群体开发了这一方案。这项工作的结果将提供一个多管齐下的框架，以更好地理解硅藻的主要进化转变。拟议的工作包括许多新的培训机会，包括微生物培养、高级显微镜以及各级初级合作者的分子和生物信息学项目。

Diatoms (microscopic marine plants) are ecologically and economically important; indeed, the oxygen in every fifth inhalation originates from diatoms, but some produce neurotoxins harmful to humans. They are also the most species-rich (~200,000) group of microalgae, thus rivaling the diversity of flowering plants on land. Evolutionarily, and like flowering plants, diatoms are relatively new arrivals, suggesting an exceptionally high speciation rate. My long-term research objective is to evaluate the evolutionary significance of the processes and structures associated with diatom reproduction in order to understand what role various types of sexuality might have played in the spectacular diversification of diatoms since their first appearance in the Jurassic Period fossil record. The immediate objectives specific to this proposal are to apply reproductive, developmental and molecular approaches to representatives of two major transitions in diatom evolutionary history to untangle their relationships to each other and to their closest relatives. I propose to investigate two orders of diatoms that currently seem to poorly or uncertainly fit in both traditional and molecular phylogenies ("family trees"). Thalassiosiroids differ dramatically from their closest relatives, and biddulphioids are likely to hold evidence that indicates the closest living relative of the most advanced of the diatoms, the pennates. We will search for developmental indicators of how these ill-fitting or uncertain characters came to be. We will use advanced microscopical techniques (light and epifluorescence microscopy, scanning electron microscopy, X-ray microanalysis, silica-specific stains) to detect and localize opaline silica (the building blocks of diatom cell walls) and describe the fine structure of the cell-wall components during their developmental stages. We will also use a heretofore underutilized molecular tool, ITS2 consensus secondary structure models, in our phylogenetic inferences. Our reconnaissance work has shown that these models are as useful in untangling diatom phylogenetic relationships as they have proven to be in green algae and other plants. Phylogenetic analysis of these diatoms combined with the ontogenetic approach we propose here is novel in diatom evolutionary biology. We pioneered this integrative approach only about a decade ago and are the only laboratory in the world to systematically add reproductive data to the wider body of diatom evolutionary biology. The major obstacle to further advancement is the lack of reproducible sex-induction protocols, which we now have developed for the diatom groups involved. The results of this work will provide a multi-pronged framework to better our understanding of major evolutionary transitions in diatoms. The proposed work includes many new training opportunities, including microbial culturing, advanced microscopy, and molecular and bioinformatics projects for junior collaborators at all levels.